Aberrations
The idea of the eye as perfect optical device we have been acquiring it since school when studying the physics section “Optics”. When studying relevant sciences in higher or secondary specialized educational institutions This idea of the eye is consolidated, acquiring additional information. Therefore, the statement of S.N. Fedorov that the eye is an imperfect instrument and the task of the ophthalmologist is to improve it, for a long time was viewed with skepticism by many doctors.
What is laser correction if not the improvement of nature's mistakes? Errors of nature here include myopia, farsightedness and astigmatism. And not only. Optical scientists have known about this for a long time. They knew that when designing even the simplest telescope, it is necessary not only to focus the optical system at one point (to exclude nearsightedness, farsightedness and astigmatism of the telescope), but also to ensure the quality of the resulting image. The lenses from which a telescope is made should be of good glass, almost perfect shape and with a well-treated surface. Otherwise, the image will be unclear, distorted and blurry. That's when the study of aberrations began - the smallest roughness and unevenness of refraction. And with the advent of devices for identifying and measuring aberrations of the eye, a new dimension entered ophthalmology - aberrometry.
Aberrations can be of different orders. The simplest and most well-known aberrations are actually myopia, farsightedness and astigmatism. They are called defocus or aberrations of the second, lower order. Aberrations of the highest order are the same roughness and unevenness of refraction that were already mentioned above.
Higher order aberrations are also divided into several orders. It is generally accepted that the quality of vision is affected by aberrations mainly up to the seventh order. For ease of perception, there is a set of Zernike polynomials that display the types of monochromatic aberrations as a three-dimensional model of refractive unevenness. A set of these polynomials can more or less accurately display any unevenness in the refraction of the eye.
Where do aberrations come from?
Everyone has them. These make up the individual refractive map of the eye. Modern devices detect higher order aberrations, which somehow affect the quality of vision, in 15% of people. But everyone has individual characteristics of refraction.
Suppliers of aberrations are the cornea and lens.
The causes of aberrations may be:
Congenital anomaly (very small irregularities that have little effect on vision, lenticonus);
Corneal trauma (the corneal scar tightens the surrounding tissue, depriving the cornea of sphericity);
Surgery (radial keratotomy, lens removal through a corneal incision, laser correction, thermokeratoplasty and other operations on the cornea);
Diseases of the cornea (consequences of keratitis, cataract, keratoconus, keratoglobus).
The reason ophthalmologists pay attention to aberrations is ophthalmic surgery. Ignoring aberrations and not taking into account their impact on the quality of vision, ophthalmology existed for quite a long time. Before this, aberrations were studied and fought against them. negative influence only manufacturers of telescopes, telescopes and microscopes.
Surgeries on the cornea or lens(meaning a corneal incision) increases higher order aberrations by several orders of magnitude, which can sometimes lead to a decrease in postoperative visual acuity. Therefore, the widespread introduction of artificial lens implantation, keratotomy and laser correction into ophthalmological practice contributed to the development of diagnostic equipment: keratotopographs appeared that analyze the refractive map of the cornea, and now aberrometers that analyze the entire wavefront from the anterior surface of the cornea to the retina.
Aberrations caused by LASIK
By correcting defocus (myopia, farsightedness), the refractive surgeon adds high-order aberrations to the patient.
Formation of a corneal flap by a microkeratome leads to an increase in higher order aberrations.
Complications during LASIK lead to an increase in higher order aberrations.
The healing process leads to an increase in higher order aberrations.
Combating LASIK-Induced Aberrations
It was not possible to remove micro-roughness and unevenness using an excimer laser with a slit beam. A device with the possibility of point ablation was invented and put into production, that is, the diameter laser beam in some models less than a millimeter. Using Zernike polynomials were introduced into practice computer programs, allowing you to automatically convert the individual refraction map obtained from the aberrometer into laser machine into an algorithm that controls the beam, eliminating not only residual defocus, but also higher-order aberrations. Zernike polynomials become a set of tools, each designed to remove a specific component in the aberration complex. Like a carpenter, a plane is for leveling, a chisel is for deepening, a saw is for dividing, an ax is for splitting. It's not that simple, of course. Just as an ax can have not one, but ten uses, a polynomial is designed to remove spatially quite complex shapes. But the basic principle is clear.
When performing such personalized laser ablation, the cornea should approach in shape to the level of an optically ideal sphere.
Super vision
After personalized laser correction, some patients achieved visual acuity of more than 1.0. Patients saw not only ten lines, but also eleven, twelve, and even more. This phenomenon has been called "supervision".
In scientific circles, a discussion has flared up almost about the violation of human rights. How correct is it to give a person too good vision, because he will see flaws on the faces of loved ones, will begin to distinguish every pixel on the computer and TV screen, and suffer from an excess of visual information. Quite a scientific approach. Maybe this debate will be relevant in a few years.
However, in parallel with this dispute, commercial proposals also appeared. Advertisements for excimer clinics promised super vision for everyone. But super vision is not predictable! Some patients will succeed, but dozens of others will not. After all, the ability to supervision is determined by the size of the eye’s photodetectors, those same cones on the retina. The smaller the cone and the greater its density in the macula, the smaller the object a person can see. In addition, the effect of each type of higher-order aberration on vision has not yet been sufficiently studied. That's why commercial offer supervision in the form of superLASIK (see above) is incorrect. We can only talk about personalized laser correction.
The effect of aberrations on vision
During the Cold War between the USSR and the USA, scientific and military-industrial espionage became one of the most important areas of work for the intelligence services of the two countries. When the new Soviet MiG fighter demonstrated in local wars a clear advantage of its technical characteristics over enemy aircraft, US intelligence did everything to take possession of the secret developments of the design bureau of Artem Mikoyan. In the end they managed to get almost a whole MiG.
One of the advantages of the MiG over its American counterparts was its maneuverability and speed, due to the extremely low air resistance during flight at that time. The air seemed to have no resistance at all to the plane’s body, smoothly flowing around its contour.
To achieve this effect, American aircraft designers tried to make the surface of their aircraft perfectly smooth, even and streamlined. Imagine their surprise when they saw the uneven, rough surface MiG with protruding heads of “rivets and bolts”. The secret of the Russian aircraft's streamlining turned out to be simple and ingenious. All these roughnesses during the flight created a kind of air cushion around the aircraft body, allowing the air resistance to be reduced as much as possible.
Perhaps this is a myth or legend of aircraft designers, but this analogy perfectly illustrates the attitude of ophthalmologists to aberrations of the highest order. The fact is that the views of ophthalmologists on the issue of the influence of aberrations on vision over the past ten years have undergone a certain evolution, similar to the evolution of American designers regarding the characteristics of the surface of an aircraft.
As mentioned above, ophthalmologists turned to the problem of aberrations close attention mainly because deterioration in the quality of vision after corneorefractive surgery. Patients saw the required number of lines, but complained of decreased dark adaptation, distortion and blurriness of the boundaries of visible objects. There were also those who, with almost zero refraction (that is, the absence of myopia and farsightedness), visual acuity was 1-2 lines short of the level they had with glasses before correction. It is not surprising that the attitude towards aberrations was purely negative, as acquired or congenital pathology. It was this attitude that caused the race for ideal corneal sphericity and super vision.
Now the opinion of ophthalmologists is changing. The first sign was the legendary ophthalmic surgeon Pallikaris (a world-famous refractive surgeon and one of the founders of laser correction).
In 2001 in Cannes, he suggested that in each person, in addition to the eye parameters recorded using modern instruments, there is also a “dynamic visual factor.” Time will tell what further research in this area will lead to. One thing is certain: Aberrations can either reduce or increase visual acuity.
Perhaps further study of the “dynamic visual factor” will be based on the following hypothesis.
LASIK results in an increase in higher order aberrations. It may not be entirely correct to narrow these aberrations to seven orders of magnitude from a scientific research perspective. What matters here is the difference in optical density in the interface area (subflap space), and the roughness of the resulting surface of the corneal bed, and healing processes (remodulation of the shape of the cornea, traction of damaged fibrils, unevenness of the epithelial layer, etc.). All this, coupled with other aberrations, leads to blurred focus on the retina and the appearance of several images. The brain, using the accommodation mechanism, selects from all the images presented the most clear and satisfying one in a given period of time (the principle of multifocality). It is the individual characteristics of the brain’s adaptation to the variability of the resulting image that will be the “dynamic visual factor” on which it depends whether a given set of aberrations will improve vision in this person or reduce its quality. And this is already connected with the balance of consciousness and subconsciousness, psychomotor characteristics, intelligence, and psychological status.
From the jungle of assumptions to specific questions.
What are aberrations?
Chromatic, astigmatism of oblique beams, coma, etc. All together they form an image of the surrounding world on the retina, the perception of which is strictly individual for each person. Each of us truly sees the world only in our own way. Only complete blindness can be the same for everyone.
Here are several types of higher order aberrations.
1. Spherical aberration. Light passing through the periphery of a biconvex lens is refracted more than at the center. The main “supplier” of spherical aberration in the eye is the lens, and secondarily the cornea. The wider the pupil, that is, the larger part of the lens takes part in the visual act, the more noticeable spherical aberration.
In refractive surgery, spherical aberration most often induces:
Artificial lens;
Laser thermokeratoplasty.
2. Aberrations of the inclination angles of optical beams. Asphericity of refractive surfaces. It represents a mismatch between the centers of images of luminous points located outside the axis of the optical system. They are divided into aberrations of large angles of inclination (astigmatism of oblique beams) and small angles of inclination (coma).
Coma has nothing to do with the known diagnosis of resuscitators. Its aberrometric pattern is similar to a circle located in the optical center of the cornea and divided by a line into two even halves. One of the halves has high optical power, and the other has low optical power. With such an aberration, a person sees a luminous point as a comma. When describing objects, people with such aberration use the words “tail”, “shadow”, “additional contour”, “double vision”. The direction of these optical effects (the aberration meridian) can be different. The cause of coma may be a congenital or acquired imbalance of the optical system of the eye. The optical axis (on which the focus of the lens is located) of the cornea does not coincide with the axis of the lens and the entire optical system is not focused in the center of the retina, in the macula. Coma may also be one of the components of refractive unevenness in keratoconus. During LASIK, coma may appear as a result of decentering of the laser ablation zone or the healing characteristics of the cornea during laser correction of farsightedness.
3. Distortion- violation of geometric similarity between an object and its image - distortion. Points of an object at different distances from the optical axis are depicted with different magnifications.
Laser correction is not a monopolist in the correction of aberrations. Artificial lenses and contact lenses have already been developed that compensate for some types of higher order aberrations.
An excursion into the ophthalmological classification of aberrations
Aberrations are divided into three main groups:
Diffraction;
Chromatic;
Monochromatic.
Diffraction aberrations appear when a beam of light passes near an opaque object. The light wave is deflected from its direction, passing near a clear boundary between a transparent medium (air) and an opaque medium. In the eye, such an opaque medium is the iris. That part of the light beam that passes not in the center of the pupil, but at its edge, is deflected, which leads to light scattering along the periphery.
Chromatic aberrations arise due to the following optical phenomenon. Sunlight, as already mentioned, consists of light waves with very different wavelengths. Visible light ranges from short-wavelength violet rays to long-wavelength red rays. Remember the little counting rhyme for remembering the spectrum of visible light - the colors of the rainbow? “Every hunter wants to know where the pheasant is sitting.”
Red, orange, yellow, green, blue, indigo, violet.
Each of these types of rays has its own refractive index. Each color is refracted differently in the cornea and lens. Roughly speaking, the image of the blue and green parts of an object is focused by the emetron’s retina, and the red parts behind it. As a result, the image of a colored object on the retina turns out to be more blurry than a black and white one. It is on the effect associated with chromatic aberrations that three-dimensional video is based.
Monochromatic aberrations, in fact, they are the main subject of study for refractive surgeons. It is monochromatic aberrations that are divided into aberrations of higher and lower orders. Low-order monochromatic aberrations: myopia, farsightedness and astigmatism. Higher order monochromatic aberrations: spherical aberration, coma, oblique beam astigmatism, field curvature, distortion, irregular aberrations.
To describe a complex of higher order monochromatic aberrations, polynomials of the Zernike (Zernike) mathematical formalism are used. It’s good if they are close to zero, and the root mean square deviation of the wavefront RMS (root mean square) is less than the wavelength or equal to 0.038 μm (Marechal criterion). However, these are the subtleties of refractive surgery.
Standard table of Zernike polynomials is a kind of set of three-dimensional illustrations of aberrations up to the seventh order: defocus, astigmatism, oblique beam astigmatism, coma, spherical aberration, trefoil, quatrefoil and so on, up to octafoil (trefoil, tetrafoil, pentafoil, hexafoil...). “Trefoils” represent from three to eight uniform sectors of a circle with increased optical power. Their occurrence may be associated with the main centripetal directions of stroma fibrils, a kind of stiffening ribs of the cornea.
The aberration pattern of the eye is very dynamic. Monochromatic aberrations mask chromatic ones. When the pupil dilates in a darker room, spherical aberrations increase, but diffraction aberrations decrease, and vice versa. With age-related decline in accommodation abilities, higher-order aberrations, which were previously a stimulus and increased the accuracy of accommodation, begin to reduce the quality of vision.
Therefore, it is currently difficult to determine the significance of positive and negative influence each type of aberration on the vision of each person.
The role of aberrometry (with keratotopography function) in preoperative examination
Everything has already been said about this. Based on aberrometry data, an individual wavefront map is compiled, based on the parameters of which personalized laser correction is carried out. In most patients, the level of higher order aberrations is, to put it mildly, very small. And there is no need to use personalized laser ablation. Autorefractokeratometry data is sufficient. But this does not mean that you should not pursue personalization. After all, if you have aberrations, they can only be identified with aberrometry. And with correction, it is more likely to obtain higher visual acuity than you ever had with glasses or even with contact lenses Oh.
Rice. 17. Eye wavefront analyzer (aberrometer with keratotopography function). The essence of keratotopography is as follows. Luminous concentric circles (Placido disk) are projected onto the anterior surface of the cornea (b) and their reflection is photographed by the apparatus (a). Based on the difference between the parameters of the projected and reflected circles, the device calculates the curvature of the cornea in 10,000 points and generates a refraction “map”.
Personalized laser ablation is also performed for additional correction, for correction after other operations, and for thin corneas.
As for diagnosis as such, that is, the search for pathology, the main thing here is not to miss keratoconus.
Once again about keratoconus
It is quite easy for a refractive surgeon to identify keratoconus with the appropriate equipment. But that's not the problem. The problem is responsibility. Just like the difficulty of a sapper’s work lies not only in knowledge of the intricacies of the craft. The difficulty is that the sapper makes only one mistake. You can't go wrong with keratoconus. Never. And to do this, you need to constantly keep in mind its indirect signs:
Myopic astigmatism is often with oblique axes;
The optical power of the cornea is more than 46 diopters;
Thin cornea;
Surprisingly good vision without glasses and surprisingly poor with glasses in the presence of severe astigmatism;
Progression of astigmatism;
Local protrusion of the cornea, often in the lower sector.
This protrusion is impossible to miss when keratotopography (or aberrometry). Protrusion is accompanied by an increase in optical power. The generally accepted color indication standard colors areas with lower optical power (diopter) in a wavefront image in blue, and areas with higher optical power (diopter) in red. Classic keratoconus appears as a red spot in the lower right or lower left sector of the cornea.
By the way, normal high degree astigmatism looks like a red butterfly. Sometimes the wings of this butterfly lose their symmetry. One wing becomes huge, moves downwards, and the other becomes smaller. Like sand in an hourglass, optical power flows from the top to the bottom. This could already be a manifestation of keratoconus. Do laser correction in this case it is impossible.
Who tolerates aberrations acquired after LASIK worse?
Young people with a labile psyche and wide pupils. Each of us has a different pupil size in light. The average is three millimeters, but some have a couple of millimeters more from birth. And the larger the pupil, the larger the area of the cornea and lens that takes part in the act of vision. And the more small roughnesses distort the image. As a rule, the brain does not pay attention to such trifles. Just like it excludes from visual information floating opacities in the vitreous body (most myopic people have them), and a person pays attention to them only sometimes, looking at blinding white snow or, say, at a bright computer screen. But in subtle, creative, nervous natures, perception is often heightened, and this may contribute to the fact that they constantly pay attention to such stimuli. This is not pickiness, but a feature of the nervous system, such as an individual pain sensitivity threshold.
In such cases, you can try to get the brain accustomed to aberrations, or rather, to divert its attention from this problem by instilling drops that constrict the pupil (pilocarpine) for a month. If this tactic fails, additional correction will have to be made in order to reduce higher-order aberrations.
Where in everyday practice might an ophthalmologist encounter higher order aberrations?
In keratoconus, visual acuity with full spectacle correction often falls short of 1.0. When testing vision through an aperture of three millimeters or less, visual acuity improves significantly (see above). In both cases, the reason for what is happening is aberrations.
After cataract removal with implantation of an artificial lens, the patient often, even with full spectacle correction, does not see 1.0. Not in all cases this is associated with retinal diseases, amblyopia or secondary cataracts.
The artificial lens is smaller in diameter than the natural one. Sometimes the artificial lens may not be level. When performing an operation with a corneal incision, the spherical shape of the cornea changes. All these reasons cause aberrations of the highest order. As a last resort, they can be reduced by carrying out personalized laser correction (more on bioptics in the next chapter).
It makes sense to carry out aberrometry in the so-called night blindness, manifested by deterioration of visual acuity at dusk, but not accompanied by signs serious illnesses retina (tapetoretinal abiotrophy, etc.).
There are many examples that can be given. If aberrations are suspected, the patient can be referred for examination to a refractive surgery center.
Article from the book:
Aberration of the eye- distortion of the image on the retina due to imperfections in the optical system of the eye. The presence of aberrations of the eye leads to the fact that each point of an object is depicted as a spot with a rather complex distribution of illumination in it.
There are diffraction, spherical and chromatic aberrations of the eye.
Spherical aberration of the eye - rays passing through the peripheral zones of the pupil are refracted more strongly than rays passing through its central zone. The effect of spherical aberration on image quality is relatively small for small pupil sizes (2–4 mm). With larger pupil sizes, the influence of spherical aberration becomes stronger, and the quality of the image on the retina deteriorates significantly. The variation in eye parameters between different people is large, even the sign of aberrations changes. Aberrations become minimal during accommodation to close objects (1–2 m). Most eyes have negative aberration. Such aberrations are typical for cases where the refraction of the cornea is high and the lens is low. If the aberration of the cornea is lower than normal, and the lens is higher, then positive aberration is more often observed.
A special feature of the eye, compared to a conventional optical system, is that spherical aberration in the eye is partially compensated. Firstly, due to the fact that the peripheral zones of the optical system of the eye have weaker refraction (lower optical power) due to the lower refractive index of the peripheral zones of the lens compared to its core. Secondly, due to a slight increase in the radii of curvature of the peripheral part of the cornea. Spherical aberration depends on accommodation; it, as a rule, increases with increasing accommodative voltage.
Chromatic aberration of the eye is the scattering of rays in the focused optical system of the eye, caused by unequal convergence of rays of different wavelengths, as a result of which the image is blurred and its edges are colored. Chromatic aberration manifests itself in the fact that a parallel beam of white light incident on the lens is focused at more than one point: short-wave rays will converge closer to the lens than rays longer length waves. This leads to the fact that the image of a white point in any plane is obtained in the form of a colored spot. If the focus of the blue rays is aligned with the retina, the image of the point will be surrounded by a red halo, and vice versa. Chromatic aberration depends on the diameter of the pupil of the eye and increases with it. The amount of chromatic aberration for the extreme wavelengths of the visible spectrum averages 1.3 diopters. This value was established by T. Jung. Under normal conditions of illumination with white light, a person does not distinguish colored borders around the observed objects. This is explained by the overlapping of colored halos one on top of the other and the small angular dimensions of the colored borders. Determination of visual acuity in monochromatic light, as well as the use of special means to correct chromatic aberration, did not lead to a significant increase in visual acuity, i.e. chromatic aberrations do not significantly affect central vision.
In addition to spherical and chromatic aberration, the eye is characterized by such aberration as physiological astigmatism. Physiological astigmatism is understood as astigmatism of the eye in which normal visual acuity is maintained. Physiological astigmatism is characteristic of each eye and is caused by several main factors: asphericity of refractive surfaces, astigmatism of obliquely incident rays, decentering of refractive surfaces and uneven optical density of refractive media. The disorder of the structure of physiological astigmatism makes it impossible to correct it with cylindrical or contact lenses. The latter are capable of correcting corneal astigmatism, but the lens component of physiological astigmatism is fully preserved. The lower the physiological astigmatism, the higher the visual acuity. This pattern is valid for visual acuity in the range 1.0–2.0, i.e. for the vast majority of normal eyes.
Diffraction aberration of the eye is diffraction that occurs when light rays pass through a constricted pupil. As the diameter of the pupil decreases, the diameter of the diffraction circle of light scattering increases. However, this reduces spherical aberration. Due to this inverse relationship best conditions The clearest observation of objects occurs with a pupil diameter of 2–4 mm. In addition, for points that do not lie on the axis of the system, other aberrations are observed, for example, astigmatism of inclined beams, coma, as well as aberrations that cause distortion of the image shape. The last of them, distortion, changes the magnification as the object moves away from the axis of the optical system.
www.eye-clinic.ru
Avitaminosis.
Regarding B vitamins, as well as fat-soluble vitamins A, E and D, then their main source is not vegetables, but high-calorie foods such as meat, liver, kidneys, eggs, milk, butter and vegetable oil, bread made from wholemeal flour, cereals that retain the outer shell rich in vitamins and minerals (buckwheat, oatmeal, millet, brown rice).
Misconception 2. Synthetic vitamins are not the answer.
And all because synthetic vitamins are supposedly not real. Those who studied chemistry well at school will immediately appreciate the comedy of this statement. Let us remind the rest: substances with the same chemical structure, but obtained in different ways, have exactly the same properties and activity.
Misconception 3. The more expensive the vitamin complex, the better it is.
Marketing is an unreliable friend. If you choose vitamins to prevent vitamin deficiency, then pay attention to several factors. The composition of magic pills must be indicated either in absolute values, or as a percentage of the daily value. It’s even better if the dosage of the tablets is calculated so that the daily requirement of vitamins is several pills. By taking them several times throughout the day, you will maintain a constant level of vitamins in your blood serum.
Misconception 4. Vitamin deficiency does not happen to anyone. Loading dose vitamins will help us.
Let's still separate the flies from the cutlets: no one can say about a slight seasonal deficiency of vitamins. Vitamin deficiency is a disease. And you shouldn’t prescribe a lethal dose of vitamins for yourself; first, it’s better to see a doctor and get examined. Its main task is to identify the ratio of vitamins and microelements in the body: what is missing and what is in excess. According to research, Russians have quite common excesses of iron, vanadium, nickel, chromium, molybdenum, boron, and even zinc, selenium and iodine, elements included in many vitamin and mineral complexes. These microelements, vital in small quantities, become toxic when in excess in the human body and can cause serious diseases.
Depending on the results of the examination, one of two technologies for vitamin and mineral correction is chosen - therapeutic or preventive.
Yulia Bogdanova
Magazine "Be Healthy"
Medportal.ru
Vitamin deficiency manifests itself when the body does not receive all the necessary vitamins and microelements; a deficiency of vitamins leads to vitamin deficiency; a lack of vitamins causes many diseases and vitamin deficiency is no exception. Vitamin deficiency: symptoms can be different, as well as treatment, and the treatment of vitamin deficiency consists of one thing, the body receiving all the necessary vitamins and microelements, minerals, etc.
Vitamin deficiency symptoms:
Insufficient amount of any vitamin in the body, or its complete absence called vitamin deficiency. Since vitamins enter the body during food intake, this disease often manifests itself as a result of poor nutrition. This mainly happens in winter, when there is an acute shortage of fresh vegetables and fruits, although in summer it is quite difficult to adhere to the daily intake of useful microelements, which is one and a half to two kilograms of vegetables, berries and fruits.
Causes of vitamin deficiency
The causes of vitamin deficiency, like any other disease, are quite banal: unbalanced diet, eating poor quality foods, smoking, environmental conditions that are far from ideal. But still, the main reason for the appearance of this disease is the lack of physical opportunity to obtain all the required vitamins from food.
In the old days, our ancestors did heavy physical work and, therefore, ate more. Their energy consumption per day averaged four thousand kilocalories. During this period, when scientific and technological progress actively steps forward, a person is freed from the possibility of performing the same amount of physical work, and accordingly, the amount of energy consumption has sharply decreased. Now their daily norm is, on average, 2500 kilocalories.
One of the most common causes of vitamin deficiency in the hands is smoking or following various diets. These categories of people are recommended to take vitamins year-round, which normalizes metabolism, renews and restores cells in the body, and improves well-being. But it is not advisable to abuse large doses of vitamins that are sold in pharmacies. It would be more logical to buy natural products that do not contain preservatives. Every person's diet must include fresh vegetables and fruits. Vitamin deficiency on the hands will soon disappear if you include sea fish in your diet in sufficient quantities, since these foods contain substances that help skin cells rejuvenate.
Vitamin deficiency on the hands appears when the body is severely lacking in vitamins A and B. In this case, the skin on the hands begins to dry, cracks appear, and dandruff appears on the head. In addition, a lack of vitamins A and B causes a weakening of the immune system and increased sensitivity of tooth enamel. To avoid this, be sure to include carrots, pumpkin, spinach and peaches in your diet. The disease can also manifest itself if a person does not consume required quantity products that contain vitamin D. You can get rid of such problems if you include sea fish and cod liver in your menu. Food should not be homogeneous, since the body also needs other products.
Treatment of vitamin deficiency on the hands
If cracks in the hands occur due to vitamin deficiency, treatment is necessary, which consists of enriching your diet with foods that contain vitamins A and E. Such foods, for example, include nuts, olive oil, herbs, fruits and orange-colored vegetables. In addition, you can purchase synthetic vitamins at the pharmacy, but it is not recommended to abuse them, since it is better for the body to provide essential vitamins through natural food. Your daily diet must include fruits and vegetables, which are best consumed raw.
When treating vitamin deficiency in the hands, the diet must include fish products, which contain many substances that promote cell rejuvenation. In the case of eating fish and fruit (just do not mix, the interval between consumption of fish and fruit should be from an hour to two) in sufficient quantities, vitamin deficiency in the hands disappears in a short time.
Vitamin deficiency photo
Treatment of vitamin deficiency - recipes
Treatment of the disease will not be difficult if its appearance is caused by poor nutrition. To do this, you need to adjust your diet: eat as much whole grain cereal as possible (the best option is oatmeal and buckwheat), try to eat foods that are minimally cooked. It is better to use unrefined oil. Fresh vegetables and fruits must be present in the diet.
The easiest way is to treat vitamin C deficiency. You need to consume more foods that contain it. These are citrus fruits, apples, red and black currants, sauerkraut.
An excellent remedy for the treatment of vitamin deficiency is rosehip infusion. Five tablespoons of berries should be boiled in a liter of water for five minutes, left in a thermos for eight hours and drunk throughout the day.
An excellent healer is viburnum, the berries of which, poured into a glass of water at 40 degrees and infused for 4 hours, should be taken orally for? glasses about three times a day.
Vitamin deficiency can be effectively treated with rowan. Infuse twenty-one spoons of berries in a thermos (fill with water at 40 degrees) for 8-12 hours and take a third of a glass orally several times a day.
Ideally, to replenish the body with the daily requirement of vitamin C, you need to drink twenty-five or more glasses apple juice plain or four glasses of peach or orange juice.
Multivitamins are harmoniously balanced, chemically pure compounds that do not have the disadvantages present in preparations of plant and animal origin. It is important not to forget that the bulk of vitamins are absorbed only with food. You should not drink vitamins with coffee, soda water or milk to avoid insufficient absorption.
Today there is a wide variety of forms of such vitamins. These are dragees, tablets, powders, capsules, liquid form. Most convenient form are a capsule that, as it moves through the intestines, loses layer by layer, as a result of which vitamins are easily absorbed inside. It should be taken whole without chewing.
The most optimal time taking multivitamin complexes - in the morning.
Taking vitamins should not exceed the daily requirement for them. An overdose can negatively affect the general condition of the body and lead to new diseases. Each person is capable of organizing proper nutrition himself in order to maximize the receipt of the microelements necessary for the body.
In folk medicine, there are many ways in which vitamin deficiency can be effectively treated.
Balanced vitamins
Garlic is considered the most effective remedy. In order to quickly replenish the vitamins missing in the body, it is enough to consume several cloves of garlic a day. You can read the benefits and harms of garlic from a previously published article.
Onions are rich in potassium, iron and other useful microelements. It contains vitamins of groups C, B, carotene, phytoncides. The monthly rate of its consumption, according to experts, should be 100-300 grams. The miraculous benefits of onions have long been proven.
A good way to overcome depressive state and fatigue can be called beets and cabbage. They also contain a complex of all the substances necessary for the body.
Five hundred grams of freshly squeezed carrot juice when consumed daily, they are of great value compared to twelve kilograms of calcium tablets.
You can prepare a mixture of dried apricots, cranberries, walnuts, lemon, and raisins. The above products must be crushed and mixed in equal parts. Then put this mass into a container and pour honey at the rate of two hundred grams per liter jar.
Birch leaves are a great help for spring vitamin deficiency. One hundred grams of young crushed leaves are washed with water, poured with 500 grams of 40 degree water and infused overnight. Take one glass two to three times a day.
In many ways, the body itself tells you what to eat. Everyone has had this feeling that they want pineapple or parsley for no reason - this is a sign from your body that you need to eat this product that you want. If you neglect your desires, you will later shell out for expensive vitamins and medicines. Eat more fruits, nuts, vegetables, mushrooms and you will never have problems with vitamin deficiency.
Ya-zdorovyi.com
What most people understand by the word vitamin deficiency is not exactly what it really means. This disease is a pathological condition of the body that occurs due to an acute lack of vitamins. This is a rather complex disease that requires examination and treatment by a doctor. What most people usually mistake for vitamin deficiency is called hypovitaminosis in the medical community, which means partial deficiency a certain vitamin(s) in the human body.
Vitamins are irreplaceable biologically active substances that serve as catalysts for various enzyme systems or are part of many enzymes. Without their participation, normal metabolism, tissue renewal and growth, and biochemical support for many body functions are not possible. Vitamin deficiency entails disruption of enzymatic reactions. Fortunately, real vitamin deficiency, i.e. an almost absolute lack of vitamins in the body is a rather rare phenomenon: it is often found among the population of the far north.
Vitamin deficiency is characterized by seasonality: it usually takes you by surprise in winter or spring. After all, if in the summer we are ready fresh salads and we eat a lot of juicy berries and fruits, then in the cold season we switch to flour, fatty foods and sweets. But experts convince us that the disease has long ceased to be purely seasonal: many people experience vitamin deficiencies throughout the year. The main reasons for such a chronic deficiency of valuable substances are poor nutrition and disturbances in the supply of vitamins with food, problems with digestion and the functioning of the gastrointestinal tract, long-term use of antibiotics, a series of stressful situations, taking antivitamins (for example, dicumarol or sincumar, which are used for increased blood clotting) , bad habits (smokers, for example, need 5 times more vitamin C than non-smokers). In children and the elderly, the appearance of vitamin deficiency is often associated with certain age-related metabolic characteristics.
Symptoms of vitamin deficiency
Common signs of this disease include pale, flaccid skin, dry, lifeless and falling hair, brittle nails and cracked lips, bleeding gums (usually when brushing teeth), chronic feelings of fatigue, irritation and apathy, as well as frequent colds and exacerbation of some chronic diseases. diseases, for example, relapses of fungi or herpes. Those who are overtaken by vitamin deficiency have difficulty waking up in the morning (with a feeling of fatigue), complain of depression, absent-mindedness and poor concentration. Vitamin deficiency often leads to poor vision and problems with the digestive system.
In case of a catastrophic lack of a certain vitamin in a patient against the background common symptoms More specific ones may also develop. Thus, with vitamin A deficiency, chicken (or night blindness), dystrophic changes skin glands, skin and mucous membranes, a tendency to the appearance of pustules. Infectious damage to the respiratory, digestive and urinary organs is also possible, and in children - disorders in the nervous system and developmental delay.
With a lack of vitamin B1, the cardiovascular system suffers and peripheral nerves. Worried about rapid heartbeat and shortness of breath when physical activity, headaches, fatigue, swelling and low blood pressure.
If the body lacks riboflavin, i.e. vitamin B2, the patient’s appetite decreases, twilight vision is impaired and the condition of the skin and mucous membranes worsens. Conjunctivitis or aphthous stomatitis may appear, some feel pain in the eyes and burning of the skin. With a prolonged course of the disease, disturbances in the functioning of the nervous system occur, which can lead to anemia.
Deficiency of nicotinic acid (vitamins PP, B3 and B5) is accompanied by a disease such as pellagra. Some patients complain of erosive, Achilles gastritis or polyneuritis, and in more severe cases they may experience convulsions and instability when walking.
The development of scurvy and anemia can be caused by a lack of vitamin C in the body. Patients with this problem report general weakness, constant bleeding from the gums, an exhausted nervous system, increased fragility vessels.
A lack of vitamin D also has an adverse effect on health: children develop rickets, adults suffer from joint and muscle pain and dental problems.
Treatment of vitamin deficiency
The most important weapon in the fight against of this disease is balanced daily diet, providing the body with the necessary complex of carbohydrates, fats and proteins. Throughout the year, and especially on winter and spring days, you need to eat plenty of vegetables (if you run out of fresh ones, then canned tomatoes and cucumbers, sauerkraut can be a good alternative), various greens, fruits (both fresh and frozen), fish and poultry (for better preservation of vitamins, their meat should be baked in foil). All these products are rich in many valuable components, incl. and easily digestible amino acids.
If during diagnostics (sometimes a blood test is performed to check the level of vitamins) a clear lack of a certain vitamin is revealed, you will have to rely on foods with a high content of it. Please note that they are rich in pro- and vitamin A egg yolk, carrots, butter, tomatoes, fish liver, apricots. Vitamin B1 is found in sufficient quantities in yeast, wheat rye bread, peas and pork, B2 - in dairy products and various cereals, and nicotinic acid- in fish, nuts, legumes, poultry, whole wheat and lean meats. Those who lack ascorbic acid. And anyone who is deficient in vitamin D will have to make friends with herring, sour cream and beef liver.
For vitamin deficiency, vitamin-mineral complexes are always prescribed. They are produced in tablets, powders, dragees, and lozenges. But their most optimal form is considered to be a capsule. Moving through the intestines and losing layer after layer, it allows the vitamins to be gradually absorbed one by one.
Hnb.com.ua
An insufficient amount of any vitamin in the body or its complete absence is called vitamin deficiency. Since vitamins enter our body during food intake, the above-mentioned disease often occurs precisely because of poor nutrition. As a rule, in winter, when the shortage of fresh vegetables and fruits is especially great.
However, in spring and summer it is quite difficult for city residents to adhere to the daily intake of useful microelements, which ideally amounts to as much as 1.5-2 kilograms of vegetables, berries and fruits.
Symptoms
Nowadays, I’m sure you won’t surprise anyone with an unbalanced, irregular diet, eating poor quality foods, smoking, etc. And the environmental situation is far from ideal.
Vitamin deficiency also experienced a certain negative evolution. First of all, it has ceased to be seasonal. Now this disease can be observed on an ongoing basis throughout the year.
The presence of vitamin deficiency in a person can be determined by the following symptoms:
dry flaky skin, the appearance of inflammation in some areas, ulcers in the corners of the mouth, cracked lips, the appearance of rough scales of the epidermis;
brittle peeling nails, the appearance of spots and stripes on the nail plate;
swelling and redness of the eyelids, tearing, intolerance to bright light (photophobia), double vision, decreased quality of vision;
bleeding gums, crumbling and loose teeth, discoloration of the tongue, its swelling, the appearance of plaque on it;
swelling of the face and hands, not associated with alcohol abuse, various pickles, spices and marinades;
cramps, numbness, muscle pain, poor coordination of movements;
changed or increased body odor;
constant feeling of cold;
irritability, insomnia, depression, apathy, lack of energy, weakness;
failure in digestive system: constipation, diarrhea, nausea, loss of appetite, weight gain;
lack of sexual desire.
Diet
Treatment of vitamin deficiency will not be difficult if its appearance is caused only by poor diet. You just need to adjust your diet: eat as much whole grain cereal as possible (the best option is oatmeal and buckwheat), try to serve foods that are minimally cooked. When consumed bakery products preference should be given to those made from wholemeal flour. It is better to use unrefined oil. Fresh vegetables and fruits are a must in your diet.
At the same time, under no circumstances should you give up animal products. The required daily amount of vitamin A is contained in the yolks of chicken eggs, beef liver, fish oil. An excellent source of essential vitamins fermented milk products(kefir, yogurt, fermented baked milk), which also contain a lot of calcium.
If we're talking about about the treatment and prevention of vitamin C deficiency, you should consume more foods that contain vitamin C: citrus fruits, apples, red and black currants, sauerkraut.
In fact, every person, in order to maximize the receipt of microelements necessary for health, if that is what he wants, is quite capable of organizing proper nutrition.
Folk remedies
We bring to your attention some means that people have long used to combat vitamin deficiency.
One of the best among them is the infusion rosehip. You need to take five tablespoons of berries and boil them in a liter of water for five minutes. Then leave in a thermos for eight hours and drink throughout the day.
Excellent natural medicine is viburnum. Its berries, poured into a glass of boiling water and infused for four hours, should be taken orally half a glass about three times a day.
Vitamin deficiency is effectively overcome rowan. Twenty-one tablespoons of bitter berries should be infused in a thermos for three hours and taken orally, a third of a glass, several times a day.
Considered to be very effective garlic. To quickly replenish the vitamins missing in the body, it is enough to eat a few cloves of garlic a day. If this method is not suitable due to the pungent odor, you can make a tincture of garlic. To prepare it, the cloves of the plant are poured with three hundred grams of alcohol and left for three weeks in a tightly closed container. Use the prepared drug up to three times a day in the amount of twenty drops, which are diluted in half a glass of milk.
Onions also rich in potassium, iron and other beneficial microelements. It contains vitamins of groups C, B, carotene, phytoncides. The monthly consumption of onions, according to experts, should be 600-700 grams.
A good remedy for relieving depression and fatigue is beets with cabbage. They also contain a complex of substances necessary for the body.
Five hundred grams of freshly squeezed carrot juice, if consumed daily, has more value than twelve kilograms of calcium tablets! Naturally, it is impossible to drink such an amount of juice every day, but a more modest dose is quite accessible.
It is easy to prepare a mixture of dried apricots, cranberries, walnuts, lemon and raisins. The above products need to be crushed in equal parts, mixed, then put the resulting mass into a container and pour honey at the rate of two hundred grams per liter jar. Eat tablespoons throughout the day.
Helps with spring vitamin deficiency birch leaves. One hundred grams of young crushed leaves are washed with water, poured with 500 grams of boiling water and infused for four hours. Take one glass two to three times throughout the day.
It is considered to be an excellent remedy against vitamin deficiency in folk medicine. tree buds. A spoonful of such raw materials should be boiled for a quarter of an hour over low heat in a glass of water, without bringing to a boil. Leave the resulting mixture for four hours. Strain, mix with honey and drink a glass of the prepared broth up to three times a day.
You can get rid of vitamin deficiency with the help of aspen tincture. 15 grams aspen bark infuse in one hundred grams of vodka or 70% alcohol in a tightly sealed container for ten days. Take 30-40 drops, previously diluted in 50 ml of water, twice a day.
In the form of a decoction or jam, it is recommended to use regular pine needles To prepare the decoction, you need 40 grams of fresh, pre-washed pine needles. Boil it in a glass of water for about twenty minutes and strain. Take half a glass at least three times a day. Pine needle jam is prepared as follows. Three glasses of young spruce shoots are covered with 1.5 glasses of granulated sugar and poured with two glasses of water, after which they are cooked over low heat for about twenty minutes. It turns out to be a tasty and extremely healthy remedy for tea.
Vitamin deficiency can be effectively treated using herbal collections
In equal parts we take the following plants: leaves of nettle, mint, raspberry, black currant, elderberry flowers, coltsfoot and oregano grass, rowan fruits. Mix. Infuse a tablespoon of the resulting mixture with a glass of boiling water for several hours, then filter. You need to drink the drug three times a day, half an hour before meals, a quarter glass.
Rose hips, raspberry, currant and lingonberry leaves are taken in equal parts. A tablespoon of the above composition, infused for eight hours, should be taken one fourth of a glass four times throughout the day.
Mix two parts lingonberry fruit, three parts rose hips, three parts nettle leaves. Brew two tablespoons of this mixture with a glass of boiling water. Simmer for 15 minutes in a water bath, leave for one hour, filter. You should take a glass of decoction three times a day.
Pour boiling water over a tablespoon of crushed rowan and rosehip fruits and let it brew for a while. The resulting product should be consumed in a glass three times a day.
Vitamins and complexes
Ideally, to replenish the body's daily requirement of vitamin C, you need to drink twenty-five or more glasses of pure apple juice or four glasses of peach or orange juice.
To obtain vitamin B1 in full, you need to eat up to a kilogram of black bread and half a kilogram of lean meat.
And to get calcium, drink one and a half liters of milk daily and eat about three hundred grams of hard cheese&
Our ancestors led much more active image life and worked hard, expending energy and strength. If you start eating like this, then the problem with vitamin deficiency will most likely be solved, while gaining new excess weight.
That’s why it makes sense to use vitamin complexes, available in a variety of dosage forms. If such complexes are taken in therapeutic doses, they do not accumulate in the body and do not produce side effects. There is no need to be afraid of using and synthetic vitamins. They also don't cause side effects and allergic reactions.
Modern multivitamins are harmoniously balanced, chemically pure compounds that do not have the disadvantages present in preparations of plant and animal origin. It is just important not to forget that the bulk of vitamins are absorbed only with food, and that you should not drink vitamins with coffee, soda water or milk to avoid insufficient absorption.
Today there is a wide variety of options for such vitamins: dragees, tablets, powders, capsules, liquid form. The most convenient form is a capsule, which, as it moves through the intestines, loses layer by layer, as a result of which the vitamins are easily absorbed. The capsule should be taken whole without chewing.
The most optimal time to take multivitamin complexes morning hours.
The consumption of vitamins should not exceed the daily requirement for them! An overdose threatens to negatively affect the general condition and lead to new ailments.
www.km.ru
Avitaminous and hypovitaminous keratitis.
Avitaminous- adj. 1. ratio with noun vitamin deficiency associated with it 2. Characteristic of vitamin deficiency, characteristic of it. Dictionary Efremova. T. F. Efremova. 2000 ... Modern explanatory dictionary of the Russian language by Efremova
avitaminous- avitaminous, avitaminous, avitaminous, avitaminous, avitaminous, avitaminous, avitaminous, avitaminous, avitaminous, avitaminous, avitaminous, avitaminous, avitaminous, avitaminous, avitaminous, avitaminous, ... Forms of words
avitaminous- vitamin avitamin ... Russian spelling dictionary
Avitaminous keratitis- Avitaminous keratitis is an inflammation of the cornea associated with metabolic disorders. It is fraught with perforation of the cornea and complete loss of vision. Symptoms of vitamin deficiency keratitis May occur when poor nutrition and gastrointestinal diseases... Wikipedia
keratosis follicular avitaminous- see phrynoderma ... Big Medical Dictionary
vitamin deficient diarrhea- (d. avitaminosa) P., caused by a deficiency of certain vitamins (group B, PP) ... Large medical dictionary
phrynoderma- (phrynoderma; Greek phrynos toad + derma skin; synonym keratosis follicular avitaminous) follicular keratosis, in which areas of keratinization are surrounded by a zone of depigmentation; manifestation of hypovitaminosis A ... Big medical dictionary
Frinode?rma- (phrynoderma; Greek phrynos toad + derma skin; synonym keratosis follicular avitaminous) follicular keratosis, in which areas of keratinization are surrounded by a zone of depigmentation; manifestation of hypovitaminosis A. Phrynoderma hypothyroidism (p. ... Medical encyclopedia
AVITAMINOSIS- AVITAMINosis, huh, husband. (specialist.). A disease caused by a severe lack of vitamins in the body. | adj. vitamin deficient, oh, oh. Ozhegov's explanatory dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 ... Ozhegov's Explanatory Dictionary
Keratitis- ICD 10 h36 ... Wikipedia
Dic.academic.ru
| General symptoms of keratitis 1. Subjective signs in the form of corneal syndrome (photophobia, lacrimation, blepharospasm, feeling of a foreign body under the eyelid). 2. Objective signs: pericorneal or mixed injection; the presence of corneal infiltrate (superficial or deep, with or without corneal erosion); neovascularization of the cornea (superficial, deep, mixed); change in corneal sensitivity (preserved, reduced, absent); as a result of the process, scar formation - varying degrees of corneal opacification; with some keratitis, anterior uveitis (iridocyclitis) may be associated; with severe purulent keratitis, perforation of the cornea is possible with the development of endophthalmitis or panophthalmitis and death of the eye. |
| General principles of treatment of keratitis: most keratitis is treated in a hospital; carry out local and systemic etiological therapy (antibacterial, antiviral, antifungal and other drugs); topical non-steroidal anti-inflammatory drugs ( eye drops“Diklo-F”, “Naklof”) and systemically (orally, intramuscularly); To stop the ulceration process, extinguish the ulcer with 1% alcohol. r-rum shaved. green or 5-10% alcohol. iodine solution or cryo-, thermo-, or diathermocoagulation of the edges and bottom of the ulcer; at the stage of cleansing the ulcer, drugs that improve corneal regeneration (eye gels “Korneregel”, “Solcoseryl”, “Actovigin”); for symptoms of iridocyclitis, mydriatics (atropine in drops or under the conjunctiva); in the formation of corneal opacities, GCS drugs in the form of drops or electrophoresis (dexamethasone, etc.) and proteolytic enzymes also in the form of electrophoresis (lidase, collalizine). in severe cases, surgical treatment: washing the anterior chamber with antibiotics, therapeutic keratoplasty. |
EYE ABERRATION- distortion of images on the retina of the eye as a result of imperfections in its optical system.
EYE ABERRATION may be due to for various reasons: irregular shape surfaces of the cornea and lens, imperfection of their centering, heterogeneity of the ocular media (especially the lens) and diffraction phenomena that occur in the eye along the path of a light beam (light waves bending around obstacles, etc.).
The optical system of the human eye is inherent to one degree or another in all types of aberration of optical systems: spherical, chromatic, as well as diffraction aberrations and astigmatism (see Aberration, Astigmatism of the eye).
Spherical aberration of the eye due to the heterogeneous structure of the lens. It is defined as the difference between the degree of refraction by the optical system of rays passing through the peripheral and central parts of the pupil of the eye, and is measured in diopters. One diopter (1 diopter) is the refractive power of a lens with a focal length of 1 m. Spherical ABERRATION OF THE EYE is considered positive if the peripheral rays are refracted stronger than the central ones and their focus is closer to the lens than to the retina, and negative if the focus of the peripheral rays is closer to the retina than to the lens. The lack of a single focus for the central and peripheral rays incident on the pupil leads to the fact that the luminous points in question are projected on the retina of the eye in the form of spots (light scattering circles). As a result, visual acuity decreases.
The spherical aberration of the eye is corrected to a certain extent by reducing the curvature of the surfaces of the cornea and lens as we move from their central zones to the peripheral ones. Spherical ABERRATION OF THE EYE depends on the state of accommodation of the eyes (see) and the width of the pupil. Typically, in daylight (pupil diameter 3-4 mm), the aberration of the eyes is 0.5-1 diopters.
Chromatic aberration of the eye is caused by unequal refraction by the optical system of the eye of light rays with different wavelengths (see Refraction of the eye). It is not the same for different people. Chromatic aberration is numerically characterized by the difference between the refractive power of the eye for yellow radiation with a wavelength of 587.6 nm (5876A) and the refractive power of the eye for a given wave and is expressed in diopters.
As a result of chromatic aberration, images of objects on the retina of the eye are surrounded by a colored border. However, due to the selective sensitivity of the retina to radiation of different wavelengths, a person does not notice the colored contours of objects.
Chromatic aberration of the eye explains the inability of an eye with normal refraction (see Emmetropia) to see distant blue or violet objects, as well as the phenomena of “protruding” and “receding” colors. In many cases, chromatic aberration of the eye explains the peculiarities of the techniques used by artists in landscape and tailor painting.
A number of methods and instruments used in ophthalmology to measure the amount of ametropia of the eye are based on the use of the phenomena of chromatic aberration of the eye. Diffraction aberrations of the eye are distortions on the retina of the eye as a result of diffraction that occurs when light rays pass through a small diameter pupil. In diffraction aggregation, point objects are depicted on the retina not in the form of dots, but in the form of round spots surrounded by rows of light and dark rings. The diffraction aberration of the eye appears more sharply, the smaller the diameter of the pupil.
The greatest clarity of the image of objects on the retina of the eye, and therefore the best vision of the eye, occurs with a pupil diameter of 2-4 mm. A further increase in pupil diameter is accompanied by a decrease in visual acuity.
L. N. Gassovsky.
ABERRATIONS AS AN IMPERFECTION OF THE EYE Aberration is any angular deviation of a narrow parallel (collimated) beam of light from the point of ideal intersection with the retina in the center of the foveola as it passes through the optical system of the eye.
A chromatic diffraction monochromatic Higher order Spherical Coma Astigmatism of oblique beams Field curvature Distortion Irregular Low (1, 2) Ametropia Astigmatism
REASONS FOR ABERRATIONS Shape and transparency of the cornea and lens; retinal condition; transparency intraocular fluid and vitreous body. Increase in pupil diameter. If, with a pupil diameter of 5.0 mm, 3rd order A prevails, then when it increases to 8.0 mm, the proportion of 4th order A increases. The critical pupil size at which A of higher orders have the least influence = 3.22 mm. Accommodation. With age, A increases, and in the period from 30 to 60 years, A of higher order doubles, because over time, the elasticity and transparency of the lens decreases, and it ceases to compensate for corneal A. Accommodation spasm is an excessively persistent tension of accommodation caused by such a contraction of the ciliary muscle , which does not disappear under the influence of conditions when accommodation is not required. Condition of the tear film. When the tear film is destroyed, A of higher orders increases by 1.44 times. One type of tear film disorder is dry eye syndrome. Wearing contact lenses. Soft CLs can cause high-order wave monochromatic A, while hard CLs reduce 2nd order A. However, the asphericity of the surface of hard CLs may be the cause of SF. A. Aspheric CLs may cause greater instability of visual acuity than spherical CLs. Multifocal CL can induce A-type coma and 5th order.
CHROMATIC ABERRATION This is a distortion of the image due to the fact that visible light rays, having different lengths waves and falling on the lens in a parallel beam, refracted, are focused at more than one point. CVL (blue-green) focus further from the retina than DV (red). This is chromaticism of position. As a result, the image is blurred and its edges are colored. If the focus of the blue rays is aligned with the retina, the image of the point will be surrounded by a red halo, and vice versa. The outlines of perceived objects can be colored red in case of hypermetropia, and blue in case of myopia. The practical significance of CA is more noticeable when performing a duochrome test to clarify the optical alignment of the eye with ametropia. Under conditions of illumination with white light, a person does not distinguish colored borders around the observed objects. This is explained by the overlapping of colored halos one on top of the other and the small angular dimensions of the colored borders. CAs do not have a significant effect on central vision.
DIFFRACTION Associated with the violation of straightness, deflection, of a light wave as it propagates past the sharp edges of opaque or transparent structures that form holes. This structure in the eye is the pupil. As a result of the diffraction of light at the border of the pupil, where, according to the laws of geometric optics, there should be a clear transition from shadow to light, a series of light and dark diffraction rings appear, projected onto the retina. As the diameter of the pupil decreases, the diameter of the diffraction circle of light scattering increases. But at the same time, spherical aberration decreases.
SPHERICAL There is a difference in the refraction of a light beam between the center of a spherical optical surface and its periphery. At the heart of the sf. And lies the curvature of the cornea and lens. The influence of sf. And the quality of the image depends on the size of the pupil. For small pupil sizes from 2 to 4 mm sf. A is minimal, but increases sharply with pupil dilation. If the refraction of rays through the peripheral part of the pupil is stronger than through the central part, then sf. A is called positive (for example, with an unchanged cornea). In the opposite position, negative spherical aberration occurs (for example, when the center of the cornea is flattened after laser photoablation). Sf. And it is individual in nature. The surface of the lens, which is also individual, can partially compensate for the sf. And the corneas.
ASTIGMATISM This is A inclined beams (A large angles of inclination). It occurs due to the asphericity of the refractive surfaces of the eye. If a narrow beam of rays located at a considerable distance from the optical axis is directed at the optical system, then it will be focused in the form of two mutually perpendicular segments at a certain distance from each other, forming an image in the form of the well-known Sturm conoid (an ellipse followed by a circle, and again an ellipse). This state is equivalent to direct incidence of rays on a toric surface. Astigmatism reduces visual resolution. Special case astigmatism physiological. He retained normal visual acuity. It is caused by several factors: asphericity of the refractive surfaces, astigmatism of oblique rays, decentering of the refractive surfaces and differences in the optical density of the refractive media.
COMA Occurs when the centers of images of luminous points located outside the axis of the optical system do not coincide (aberration of small angles of inclination of optical beams). The overlay of images takes the form of an asymmetrical spot resembling a comma. One of the causes of coma is the lack of alignment between the optical centers of the cornea, lens and foveola. Decentration of new optical zones with various methods of surgical correction of ametropia can lead to increased coma. Scheme of coma formation: rays arriving at an angle to the optical axis are collected at more than one point
IMAGE FIELD CURVATURE This is due to the fact that the image of a flat object is sharp not in a plane, as it should be in an ideal optical system, but on a curved surface. It represents the middle surface between both astigmatic ones, which arise due to the mapping of each point of the segment by two images lying in the sagittal and meridional planes.
DISTORTION The geometric similarity between the object and its image is violated. At D linear increase different parts The images are different within the entire field, since points of the object at different distances from the optical axis are imaged with different magnifications. A rectangular image can become “barrel-shaped” (- D) or “cushion-shaped” (+ D). The same effect can be created by astigmatic spectacle lenses that compress or stretch objects in one direction.
THE MAP OF OPTICAL DEVIATIONS OF REAL LIGHT RAYS FROM IDEAL RAYS IN THE PUPIL PROJECTION IS CALLED WAVEFRONT. An optical system with a minimum amount of aberrations has a flat, or spherical, wavefront. In a real physiological optical system there are always deviations from a plane wavefront.
SO, AN EYE WITHOUT ABERRATIONS HAS A FLAT WAVEFRONT AND GIVES THE MOST COMPLETE IMAGE ON THE RETINA OF A POINT SOURCE (THE SO-CALLED “AIRY DISC”, THE SIZE OF WHICH DEPENDS ONLY ON THE DIAMETER OF THE PUPIL). But normally, even with 100% visual acuity, optical defects in the light-refracting surfaces of the eye distort the path of rays and form an incorrect wavefront, resulting in a larger and asymmetrical image on the retina.
A quantitative characteristic of the optical quality of an image is the root mean square value of the errors in the deviation of the real wavefront from the ideal one. To describe wavefront aberrations, a series of polynomials of the Zernike mathematical formalism are used. Prismatic tilt is described by polynomials of the 1st order (Z 1), defocus and astigmatism - by the 2nd, which are classified as 3rd, and spherical aberration by the 4th order. Higher orders are known as irregular aberrations.
How the wavefront is measured An optical system is considered good if the Zernike coefficients are close to zero and, therefore, the root mean square value of the wavefront errors is less than 1/14 of the light wavelength (Marechal criterion). Based on the data of this coefficient, it is possible to predict visual acuity by simulating the image of any optotypes on the retina. To determine aberrametry visual system human being used special device- aberrometer.
Methods for determining eye aberrations Currently, several methods are known for determining eye aberrations based on different principles. 1. Analysis of the retinal image of the target 2. Analysis of the reflected beam emerging from the eye 3. Based on compensatory adjustment of the light beam incident on the foveola
An optical system ideally corrected for all aberrations cannot provide an accurate image of the object! A point is never represented by a dot. The reason is related to the wave nature of light, which creates diffraction phenomena. A point source of light is depicted on the retina not as a single point, but as a lighter spot surrounded by a number of concentric lighter rings of decreasing brightness (Airy disk). The quality of visual perception depends on the resolution of the retina, the diffraction of light in the pupil area and the properties of the optical media of the eyes. One of the features human eye is the presence of the depth of the focal area, within which there may be no change in image quality. Visual perception is regulated not only by physiological optics, but also by the cortical structures of the central nervous system. By improving the optics of the eye by reducing aberration, visual resolution can be increased from normal levels to higher levels.
CLINICAL ROLE OF A AND ABERROMETRY The severity of A depends on many factors, which include pupil size, patient age, refraction, accommodation. And they are not constant and change over time with a frequency of about 2 Hz. Character A can even change the direction of a person’s gaze, which is necessary when examining objects. The Stiles-Crawford effect, in which the light beam in the central zone of the pupil is brighter than in its peripheral part, partially softens A. B normal eyes the average value of A of the highest order with a pupil diameter of 5 mm is 0.25 µm, which is adequate to 0.25 diopters of defocusing. As level A increases, their values can exceed normal values by 2-10 times.
Laser photoablation of the cornea in its various variants during surgical correction of ametropia makes it possible to obtain high visual resolution, but at the same time increases higher-order A, which manifests itself with a pupil diameter of 5 mm or more. At practical application optical means and surgical methods There are factors that limit visual resolution capabilities. For example, any dynamic changes in the parameters of accommodation or the pupil will lead to distortions on the retina due to residual A. Statistical correction A is not capable of making the eye free from their undesirable influence. Only dynamic correction based on the principles of adaptive optics, used in fundus visualization, is free of disadvantages. The elimination of monochromatic A immediately leads to the dominance of chromatic ones. And it is impossible to eliminate the light scattering effect even if A is eliminated.
Achieving super vision with complete correction of the A eye is hardly possible or advisable! Firstly, the A's themselves are dynamic. Second, there are neuroreceptor limitations on visual resolution caused by the location of the retinal photoreceptors. Increased visual resolution may cause visual illusions. The positive role of high order A's is that they increase the depth of the focal area. If these A are eliminated, maintaining only ametropia, then a contrast inversion of the perceived images will occur - white and black will change places. given situation A are a mechanism for correcting image quality. The absence of A, which creates a low level of defocusing, would partially eliminate the stimulus for accommodation, disrupting its operation and reducing the accuracy of accommodation.
Aberrations are optical defects in the human eye that distort the image on the retina and impair the quality of vision (in about 15% of people). Their occurrence is associated with the structural features of the refractive media of the eye.
There are aberrations:- diffraction. Part of the light beam passing at the edge of the pupil is deflected, the light is scattered around the periphery;
- chromatic. Associated with the peculiarities of color perception by the optical system of the eye. The defect manifests itself in the fact that the image of a colored object on the retina turns out to be blurry, while a black and white object is clearer;
- monochromatic. They can be of different orders and are the subject of study by refractive surgeons.
- higher order (15%): spherical aberration, oblique beam astigmatism, irregular aberrations, field curvature, distortion, coma;
- lowest order (85%): astygamatism, farsightedness, myopia.
The occurrence of defects is associated with the peculiarities of the passage of light through the optical media of the eye. Namely: tear film, cornea, aqueous humor, lens, vitreous body.
The causes of aberrations may be:- dry eye syndrome, which causes a deficiency of the tear film;
- postoperative scars on the cornea;
- eye injuries;
- infectious diseases of the eye;
- cataract;
- corneal diseases (keratoconus, keratoglobus);
- changes in the vitreous body, characteristic of myopia;
- hemorrhages, etc.
Polynomials of the Zernike (Zernike) mathematical formalism are used to describe a complex of higher order monochromatic aberrations. This is a set of three-dimensional illustrations of aberrations up to the seventh order.
Diagnosis of aberration defects is carried out using the so-called. wavefront analyzer. This method is based on computer analysis of the deviations of light rays as they pass to the retina of the eye, followed by partial reflection.
Patients are examined using an aberrometer. The device accurately determines all errors in the optical system of the eye, and also allows us to judge their impact on the quality of vision.
Treatment of higher order aberrations
Defects in the optical system of the eye are, to one degree or another, inherent in every person. If aberrations do not impair the quality of vision and do not limit professional activity patient, they do not require specific correction.
Otherwise, special adaptive optics are offered. For example, glasses, contact and intraocular lenses. The use of wavefront technology allows you to choose the optimal way to compensate for the effect of aberrations on the quality of vision.
In addition to adaptive optics, the patient can use refractive surgery methods. They are aimed at changing the refractive power of the cornea. Based on aberrometry data, surgical vision correction is performed.
You can get advice from competent specialists at I. Medvedev’s ophthalmology clinic.
