Age-related accommodative insufficiency, or presbyopia, is a consequence of a gradual decrease in the elasticity of the lens capsule and compaction of the lens substance, reducing the possibility of its focusing deformation.
Age-related accommodative insufficiency, or presbyopia, is a consequence of a gradual decrease in the elasticity of the lens capsule and compaction of the lens substance, reducing the possibility of its focusing deformation. The elasticity of the choroid and the contractility of the ciliary muscle also deteriorate over the years, but to a slightly lesser extent. Although the timing of the weakening of accommodation for all types of refraction is approximately the same, difficulties in reading arise first in hypermetropes, then in emmetropes, and then in myopes of the same age. With emmetropia, presbyopic manifestations become clinically significant at the age of 43-47 years. “Early” cases of presbyopia are mostly represented by unrecognized hidden farsightedness, and much less often by the consequences of excessive visual load or previous intoxication. True presbyopia in a person under 40 years of age is as extraordinary a phenomenon as good preservation of accommodation in a person over 60 years of age.
Can the severity of presbyopia decrease? It would seem a strange question, since the aging process is irreversible. Nevertheless, there are known cases of temporary early increase in the degree of presbyopia after surgical interventions under anesthesia, when, after restoration of accommodative function to the age norm (sometimes within 1-2 years), it was necessary to weaken the power of presbyopic spectacle lenses.
The generation living now, in contrast to people at the beginning of the last century, has become taller (by about 10 cm), their average life expectancy has increased (at least in civilized countries), and myopization has also increased. In other words, the average inhabitant of the planet now has stronger refraction, his age-related accommodative safety has somewhat improved, and his near working distance has increased.
All this leads to people later applying for their first presbyopic glasses and using a smaller age increase. In general, the presbyopic increase corresponds to the generally accepted one, calculated only for a significant number (20-30%) of myopes; it is less in emmetropes and even less in hypermetropes. Among our contemporaries, with an absolute visual acuity of each eye of 0.8-1.0 for a working distance of 35-37 cm, the average addition is: at the age of 40 years - 0.50-0.75 diopters; at 45 years old - 1.00-1.25 diopters; at 50 years old - 1.50-1.75 diopters; at 55 years old - 2.00 diopters; at 60 years old - 2.25 diopters; at 65 years or more - 2.50-2.75 diopters.
We share the opinion of Yu. I. Vyazovsky, who believes: “The process of selecting a presbyopic correction does not consist in moving the nearest point of clear vision to a working distance, but in empirically determining the largest circles of light scattering (the lowest power of spectacle lenses), at which work (reading) is still possible font) at close range. This process depends not only on the volume of accommodation, but also on visual acuity and pupil diameter.”
The first presbyopic glasses for hypermetropes with full relative visual acuity forcedly and prematurely correct existing farsightedness. Having started wearing such glasses, patients note that distance vision without correction deteriorates in a short time. Working like “glass atropine,” collective spectacle lenses provoke an “accommodative collapse”: latent farsightedness turns into obvious. To mitigate this phenomenon, it should be more often recommended to choose the so-called halves as the first presbyopic glasses. The deterioration of vision at all distances associated with this transition is compensated at the working distance by the strengthening of presbyopic spectacle lenses. It seems that during this period the presbyopic gain itself “slips” or even stops in its development. Many presbyopes believe that wearing second glasses to correct decompensated hypermetropia accelerates the progression of age-related changes. In fact, normalizing the work of accommodation at a long distance increases its ability to work as a whole and ensures the physiological course of presbyopic changes. The same can be said about bifocal glasses. There is no contradiction between this and the previous theses: hidden (compensated) farsightedness does not need correction, but obvious farsightedness needs to be corrected.
Since the first presbyopic glasses form new visual habits, and the patient’s visual stereotype becomes more and more complex over the years, it is very important to select and manufacture them correctly. Therefore, the second and subsequent presbyopic glasses should not be too different from the first (previous) glasses. That is, in new glasses it is desirable to maintain the same difference in the power of corrective spectacle lenses (or its sameness) that was in the old glasses, and the correction should not be increased by more than 1.00 diopters. The above does not mean that there is no need to correct errors made in existing glasses.
When determining what glasses the patient used previously, you need to keep in mind the following circumstance. Sometimes, as old glasses, users present presbyopic glasses that they have not worn for a long time, without informing them that for the last six months or a year they have been reading with stronger glasses of their spouse (girlfriend, mother, co-worker). Quite often, the habit of wearing incorrect old, sometimes foreign, glasses becomes a cause of discomfort in new, well-chosen and correctly manufactured glasses, since many patients at one time were able to adapt to the incorrect, often excessive, intercenter distance and used glasses with similar centering for many years. Therefore, when the optical power of spectacle lenses is 2.00 diopters or more in existing glasses, it is advisable to compare the values of the center-to-center distance and interpupillary distance. If there are discrepancies of 3 mm or more, the intercenter distance indicated in the prescription for new glasses must be increased (decreased) compared to the interpupillary distance by 1-2 mm. The amendment made will make it easier to adapt to the newly selected glasses. If a patient who is accustomed to wearing glasses with incorrect center distances is not gradually taught to wear correctly centered glasses, this habit may become a contraindication for prescribing glasses with progressive spectacle lenses.
When wearing some plastic frames for many years, a deformation occurs in the area of the nasal bridge - the so-called eversion of the frame (due to heating of this place by the back of the nose), when the outer edges of the rims protrude forward in relation to the bridge and the inner edges. The fit of the glasses is disrupted, but the prismatic effect increases extremely slowly, and the patient easily and imperceptibly adapts to it. And in new, non-deformed glasses, he experiences a feeling of discomfort and spatial distortions appear. In such cases, the well-fitting new frames have to be molded to the shape of the previous glasses. The same should be done if there are other distortions in old glasses.
If the patient finds it difficult to choose between old and new spectacle lenses, although he was previously dissatisfied with the existing glasses, it is necessary to attach trial spectacle lenses +0.25 diopters (+0.50 diopters) to his old glasses while reading a standard text.
Near visual acuity due to the reduction of aberrations during pupil constriction, eikonia of collective spectacle lenses, “near” binocular summation, and other things, is often higher than at distance. In some cases, patients with absolute visual acuity of 0.1-0.2 cope with reading standard texts with prescription spectacle lenses. Occasionally, the opposite situation is observed when, with distance vision of 0.8-1.0, difficulties arise when reading with standard presbyopic correction. Deterioration in the ability to recognize letters as the distance between them decreases may occur in some forms of macular degeneration.
Overcorrection of presbyopia is relatively rare: it occurs in 2-3 out of 100 optical store clients. On the other hand, many “insensitive” presbyopes wear their mother’s or grandmother’s “inherited” strong glasses without much hassle. In women, almost every third such case is a “psychological” overcorrection (“my friend’s glasses are weaker”). Occasionally, this also occurs in men. Causes of visual discomfort with over-correction: a shift of the working zone closer to the eyes, which causes additional stress on convergence and spectacle heterophoria, as well as deterioration of vision in the near-middle zone. The tension that appears in the eyes when working in such glasses does not decrease over the next few days. It is necessary to reduce the power of corrective spectacle lenses. Some patients, especially women, have great difficulty agreeing to increasing the power of presbyopic spectacle lenses, believing that this “ages” the person, both cosmetically and psychologically.
At the same time, when presbyopic glasses become weak, patients in most cases slide them down the bridge of the nose and push the working text away. About every fourth person, after several minutes of reading in such glasses, develops a feeling of tension in the eyes, then periodically a “fog” appears. After stopping work, there is a deterioration in distance vision, which goes away within 10-15 minutes. Such difficulty in switching focus from near to far, when the patient is still without glasses, is an early symptom of impending presbyopia.
Occasionally, farsighted presbyopes may experience more pronounced accommodative inertia, which is a source of errors when selecting glasses.
Example from practice.
A 53-year-old woman is dissatisfied with her old glasses for near vision (OD Sph +2.0 D; OS Sph +3.0 D). Upon inspection: Vis OD = 0.5 not correct. Vis OS = 0.4 co Sph +1.5 D = 1.0. Rou = H 1.0-1.5 D. Fundus without pathology. After selecting a spectacle lens for the left eye, a second attempt was made to correct the right eye, which was successful. Now the eye has “accepted” the spectacle lens. Vis OD co Sph +1.25 D = 1.0. Isometric glasses were prescribed for distance and near. During the previous selection, the imaginary discrepancy was corrected. We were lucky: the accommodative tension relaxed during the reception.
As an exception, presbyopes are diagnosed with a “mobile” astigmatic axis, that is, there is a significant change in its position during the time between the selection and manufacture of glasses, sometimes very expensive (progressive or bifocal, for example), which becomes the reason for dissatisfaction with the selected correction. Mentioning this possibility and rechecking the astigmatic axes after receiving prescription lenses will bolster your credibility, although it will not save the optical store from financial loss. Occasionally, with small degrees of astigmatism in presbyopes, the zone of oscillation of the cylinder axis, with the same increase in visual acuity, can reach 30 degrees or more. With such “sectoral” astigmatism, it is advisable to limit yourself to spherical correction.
With the onset of presbyopia, a little anisometropia may well be a blessing.
Case from practice.
A 47-year-old woman, a tram conductor. For 17 years I used glasses with spectacle lenses -3.75 diopters. For the last 4-5 months he has been having difficulties making financial payments. It is inconvenient to take off your glasses - you need to control the situation in the carriage. Upon examination: Vis OD/OS = 0.1/0.1 co Sph -3.75 D/Sph -2.75 D = 1.0/1.0. Rod = M 4.0 D; Ros = M 3.0 D. The eyes are calm. Fundus - myopic cones, age-related angiofibrosis. Glasses prescribed: OU Sph -2.5 D. Vis OU v/o = 0.9-1.0. With glasses he can read fluently and clearly distinguish the denominations of coins. The selected correction preserves the existing visual stereotype, is accessible, and eliminates the problem of adaptation.
Quite rarely, when selecting presbyopic glasses, anisometropia at near and isometropia at distance is detected.
Let's give an example.
Woman 50 years old. Notes difficulty reading with old glasses. Upon examination: Vis OD/OS = 1.0/1.0. Rou = Em. With correction for near, OU Sph +1.75 D notes that the left eye sees significantly worse. Final selection: OD Sph +1.75 D; OS Sph +2.25 D. There is a fairly significant category of patients who are completely satisfied with slightly reduced vision, who consider their ametropia to be compensated (in the everyday sense, of course) and do not use correction. These people are well adapted to both everyday life and the performance of their professional duties. They turn to reading glasses (their first glasses!), just like emmetropes, only with the onset of presbyopia. Their uncriticized unilateral or bilateral (equal and different degrees) ametropia and the visual dynamic stereotype that has developed on this basis, paradoxically, can in some cases be considered as a variant of the individual visual refractive norm. It is from these positions that we need to approach the correction of presbyopia in such patients. It should often be uniformly spherical, but can be anisometropic and astigmatic. The last option for adaptation is more difficult due to the lack of habit of such glasses and taking into account the age of the users. Sometimes a gradual correction is necessary, and clear instructions about the difficulties of the adaptation period are required in each case.
Illustration from practice.
Woman, 53 years old, dentist. Within a week he cannot get used to the first presbyopic glasses prescribed at the clinic: OD Sph +1.0 D, Cyl +1.0 D ax 0; OS Cyl +1.0 D ax 180. I have not used distance glasses and do not intend to wear them in the future. Upon examination: Vis OD/OS = 0.3/0.1-0.2 s corr. Cyl -1.0 D ax 90/Sph -1.0 D, Cyl -1.0 D ax 90 = 0.8/0.8. Vis OU with corr. = 0.9. Vis OU without corr. = 0.4. The fundus is without pathology. Tn. Glasses for near vision were prescribed: OU Sph +1.0 D. Examination after 3 days: wearing new glasses he can work and read freely and feels comfortable. The main advantage of the patient's near vision was preserved - the increased length of the clinical focus, both monocular (due to astigmatism) and binocular (due to anisometropia).
Let us separately dwell on the features of spectacle correction in elderly people, who make up a very significant part of presbyopes. These are mainly unemployed pensioners with experience. It is not easy for a doctor to deal with them, since there is a known high risk of returning manufactured glasses and, accordingly, possible dissatisfaction on the part of the management of the optical store.
When selecting glasses for distance in farsighted patients over 65 years of age, a “corridor” of 1.00-1.50 diopters in length is sometimes determined with the same absolute visual acuity (usually 0.5-0.6) and subjective improvement (“I see better, sharper "), which increases as the optical power of the proposed spectacle lenses increases. The same “corridor,” including with full visual acuity and without subjective improvement (“I see the same”), can be detected when selecting reading glasses. A longer “corridor” is typical for patients with severe senile miosis, and especially for those who instill pilocarpine. If there are these “corridors”, new glasses, as a rule, should not be weaker than the existing (previous) ones. The situation becomes even more complicated if a deterioration occurs inside the “corridor” (usually a paradoxical reaction to the next 0.25 diopters), which serves as a signal for the doctor that the selection is complete. Comparison of visual acuity obtained with a new correction and with spectacle lenses additionally enhanced by 1.00 diopters, or with correction in old glasses, will help to avoid errors.
When communicating with elderly people, patience, slowness and tact, detailed, often repeated, explanations, conversations with persons accompanying them, etc. are extremely necessary. Information about the power of spectacle lenses and the center-to-center distance in previous glasses, obtained from the words of an elderly patient, is required must be rechecked. It is very important to take into account the psychological characteristics of an elderly person (touchiness, distrust, fear of being deceived), age-related changes in the whole body, eyes, visual cortex, polymorbidity, and also remember about the possible inadequacy of assessing the quality of the selected presbyopic correction due to disorders of higher neuropsychic activity, taking medications, weather dependence of patients, etc. I would also like to note cases of temporary myopization with increased blood sugar levels, persistent progressive myopization with age-related cataracts, transient visual impairment with spasms of the retinal vessels and visual centers and changes in blood pressure, decreased vision with glaucoma, retinal dystrophies, paresis of the external muscles of the eye, etc., which is often interpreted by patients as “bad” glasses. Let us especially mention the pronounced dependence of relative and absolute visual acuity on the emotional state of an elderly person.
Deterioration or improvement of vision for the above reasons, typical for elderly patients and noted at various intervals, sometimes even one-time, single, but coinciding with a visit to the ophthalmologist’s office, can become a reason for claims about the selected correction. As a rule, it is not possible to convince an elderly person of their groundlessness.
The instability of functional indicators in this category of glasses users is the main reason for the “misses” of optometrists. The second reason is a deviation from the usual correction stereotype.
In cases where there is a risk of returning glasses (the patient is excessively fussy, unsure, verbose, constantly reminds of previous glasses, disoriented in the capabilities and tasks of the doctor, is unable to clearly explain his feelings and wishes, has a lot of “bad” glasses, is dissatisfied with other ophthalmologists, excessively - even to the point of tears - expresses his gratitude, etc.), it is better to play it safe by prescribing a correction close to that in old glasses, and when making them use lenses and frames of an inexpensive price category. Let's look at two interesting examples.
Example 1.
Woman 71 years old. Complaints of a transient, sometimes alternating, decrease in distance vision due to emotional experiences while watching television series, noted over the past two months. OU are calm. Phakosclerosis, retinal angiofibrosis. Tn. Vis OD and OS during the examination range from 0.5-0.6 to 0.9-1.0 without correction and with correction Sph from +0.5 to +1.0 D. Anisometropia turns into isometropia, and vice versa. Gradually the patient calms down, vision stabilizes at 0.9-1.0 in each eye without correction. Wearing glasses for near vision (+3.25 diopters), he can read standard samples freely.
What is the reason for these fluctuations in visual acuity and correction? Apparently, mainly with vascular disorders of emotional genesis against the background of age-related changes. Such instability of visual acuity and correction, and not necessarily on an emotional basis, may not be realized by the patient and continue throughout the entire appointment. In such cases, re-examination is recommended.
Example 2.
Once, a lady 80-85 years old visited our store and could read for a short time with glasses, but only with a certain tilt of her head. And it had nothing to do with optics. It is likely that body position during reading significantly influenced the blood supply to the retina or visual cortex.
Finally, two conclusions and recommendations.
The goal of presbyopic correction is to compensate for age-related loss of accommodation with the most careful treatment of its residual function. Partially working accommodation, with restored visual performance, ensures a harmonized course of the aging processes of the eyeballs. For this reason, it is better to prescribe monofocal, bifocal or Intervista glasses for patients under the age of 55, and recommend glasses with progressive lenses for older presbyopes.
At the end of the selection, be sure to compare the vision of an elderly patient in existing and newly selected glasses. This will allow you to avoid many misunderstandings.
Alexander Lantsevich, Veko 2(86)2005
23-10-2011, 06:58
Description
Spectacle correction is one of the types of ametropia correction.
A lens is an optical transparent body bounded by refractive surfaces, at least one of which is a surface of rotation. According to the shape of the refractive surfaces of the lens, they can be:
spherical(both surfaces are spherical or one of them is flat);
cylindrical(both surfaces are cylindrical or one of them is flat),
prismatic.
Convex lenses (convex or positive) have the property of collecting rays falling on them, which is used in the correction of hypermetropia. Concave (dispersive or negative) Lenses scatter light rays, which is why they are used to correct myopia. Cylindrical lenses used to correct astigmatism. Prismatic lenses find their use for the correction of heterophoria.
All materials used for the production of spectacle lenses are divided into two classes: mineral glass (inorganic materials) and plastics (organic materials). Regardless of its nature, the material must be transparent to the visible range of light rays, homogeneous and not have high dispersion for white light, i.e. do not cause chromatic aberrations.
Based on light transmission, lenses can be distinguished: colorless, colored (sun-protective), photochromic.
Lenses are divided into groups depending on the refractive index:
With a standard refractive index (1.54, for organic materials - 1.5);
Average index (1.64 and 1.56, respectively);
High index (1.74 and 1.6, respectively);
Ultra-high index (more than 1.74 and 1.7 and above).
The use of spectacle lenses with a higher refractive index makes it possible to reduce the thickness and improve their design, reducing the prismatic effect of the peripheral part of the spectacle glass.
Based on the number of optical zones, spectacle lenses are divided into:
Single vision;
Bi- and trifocal;
Progressive.
According to the design of the lens surface, there are spherical and aspherical.
Main goal any optical correction of refractive error - moving the focal point of the optical system of the eyeball to the retina.
Indications:
Hypermetropia;
All types of complex and mixed astigmatism;
Presbyopia;
Heterophoria;
Aniseikonia.
Contraindications are relative. These include the infancy of patients, some mental illnesses, and individual intolerance to eyeglass frames.
Astigmatism. Various types of astigmatism, accompanied by a decrease in visual acuity, are considered an indication for prescription of spectacle correction.
In this case, it is necessary to determine the spherical and cylindrical correction components and the cylinder axis. The size of the spherical component is determined according to the general rules for prescribing glasses for myopia and hypermetropia. The astigmatic correction component is prescribed according to subjective tolerability with a tendency to maximum values.
If, during an additional study of refraction under conditions of cycloplegia, other values of the size and position of the cylinder axis are determined, a cylindrical component of lower optical power should be prescribed. The position of the cylinder axis, determined under conditions of cycloplegia, is considered optimal.
It should be noted that early and timely prescription of optimal spectacle correction for various types of astigmatism makes it possible to achieve good tolerability of astigmatic glasses and their high efficiency.
Presbyopia. With presbyopia, visual performance at close range is reduced, and asthenopic complaints occur.
For optical correction, positive spectacle lenses are used, taking into account preliminary spectacle correction for distance.
In this case, they are guided by age norms. The first glasses with a positive component of +1.0 D are prescribed at the age of 40-43 years, then the strength of the positive glass is increased by 0.5-0.75 D every 5-6 years. At 60 years of age, the positive correction component is +3.0 D.
The cylindrical component of the correction, as a rule, remains unchanged.
When prescribing glasses for the correction of presbyopia, their individual tolerance and visual comfort when working at close range are taken into account.
To correct presbyopia, there are bifocal glasses with a distance zone and a near zone, which allows them to be used constantly.
Currently, progressive spectacle lenses with variable optical power are becoming increasingly common for the correction of presbyopia.
A progressive lens is a lens with a gradual change in the curvature of its surface from top (distance zone) to bottom (near zone). The optical power of such a lens also changes continuously.
A progressive lens has three optical zones:
Distance zone:
The near vision zone has additional optical power (the so-called addition), which provides the necessary correction for comfortable near vision;
Intermediate zone or “corridor of progression”.
These three zones blend smoothly into one another and provide clear vision at various distances. However, the presence of zones of different optical powers leads to distortions at the periphery of the lens, which limits the field of clear vision.
The designs of modern progressive lenses take into account the solution of certain problems. For example, lenses with a special design have been created for office work, providing comfortable vision at the distances required for office space. Progressive lenses have been created that are optimized for working on a computer or specifically for reading texts, for playing sports.
In general, progressive lenses do not provide high quality vision at all distances. Specialized lenses provide visual comfort over a limited range of distances.
Heterophoria(imbalance of the extraocular muscles). Correction of heterophoria with prismatic optical elements is carried out in the event of asthenopic complaints, i.e. phenomena of decompensation.
Prismatic correction is also advisable for paresis of the eye muscles and diplopia.
Prismatic lenses have the property of deflecting light rays towards the base of the prism. Correction of heterophoria is carried out using prisms, the base of which is located in the side opposite to the deviation of the eye. With exophoria, the base is turned inward, with esophoria, outward, etc.
Before prescribing prismatic elements, ametropia is corrected according to general rules. The total force of the prismatic component is distributed equally to both eyes, while the lines of the prisms coincide, but the bases of the prisms are located in opposite directions.
Aniseikonia. A high degree of aniseikonia is considered an indication for iseikonic spectacle correction, which is carried out using specially designed glasses. Iseikonic glasses use the principle of telescopic systems. Two lenses are placed in front of each eye - positive and negative. In one case, the positive lens is located closer to the eye, in the other, the negative one. In the first case, a direct telescopic system is formed, in the other - a reverse one. In this way, it is possible to achieve approximately equal size of perceived objects.
However, at present, iseikonic glasses are used extremely rarely, since modern possibilities of contact and surgical correction of refractive errors make it possible to compensate for high degrees of anisometropia.
Criteria for optimal selection of spectacle correction:
High visual acuity:
Full functions of binocular vision;
Refractive balance determined using the duochromium test;
Good tolerance, visual comfort.
The main advantages of spectacle correction:
Availability;
No complications;
Possibility of changing the power of spectacle lenses;
Reversibility of the effect.
Main disadvantages:
Changing the size of the retinal image with high optical power lenses;
The presence of a prismatic effect on the peripheral part of spectacle lenses. The prismatic action of a positive spectacle lens leads to the appearance of ring-shaped scotomas and a narrowing of the visual field. A negative lens causes a doubling of the peripheral visual field;
The impossibility of complete correction of ametropia in cases of high degrees of anisometropia.
Alternative methods:
Contact correction of ametropia;
Keratorefractive surgeries.
Updates: no updates yetOffice glasses
Office glasses are glasses designed for working at medium and close distances. Office spectacle lenses are designed in such a way that the optical power in them smoothly changes vertically. Such lenses allow patients with presbyopia to obtain good visual acuity in the range from 30 to 400 cm (depending on the model).
Greater depth of vision is their main advantage over monofocal glasses, and a wide and comfortable middle zone over conventional progressive glasses. Therefore, office lenses are popular with people whose most of their working day is associated with visual stress at medium and close distances.
The rules for selecting office glasses depend on the type of lenses that will be installed in the frame.
Office lenses with degression
Degression means a gradual decrease in something. Degression in optics- a gradual decrease in the power of the corrective lens (here we mean positive lenses, since degression was developed for those who use “plus” glasses). Lenses with degression are designed in such a way that, regardless of the optical power at the bottom of the lens, it smoothly decreases upward by some fixed amount. The amount of degression can be from −0.75 to −2.0 D, but it cannot be chosen arbitrarily. Degression is always the same for each brand of lenses and is determined by the manufacturer.
When prescribing office lenses with degression, a prescription is selected and written as for glasses for near, the interpupillary distance for near is indicated separately for each eye and the required brand of lenses. Mark the frame with the natural position of the head.
In lenses with degression, the depth of clear vision is inversely proportional to the addition, so before writing a prescription, you need to calculate the lens power for the average distance, which is different for each patient, and offer to test the correction.
Lenses with degression are suitable:
- presbyopes of any age who require high quality vision near and at medium distances (computer users, musicians, dentists, hairdressers, etc.);
- young people with pronounced weakness of accommodation, whose work is associated with intense visual load at close and medium distances.
Office progressive lenses
Scheme of an office progressive lens Unlike lenses with degression, the optical power of progressive lenses smoothly changes from top to bottom, and distance correction is taken as the starting point. Among office progressive lenses, there are two types: in some, the manufacturer allows you to change the addition, and in others - not. Fixed addition lenses
Not exactly office-like, but they are classified as such. The amount of progression in such lenses cannot be chosen arbitrarily. Regardless of the power of the lens in the upper part, downward it changes smoothly depending on the brand of lenses: by +0.5, +0.53, +0.6 or +0.88 diopters.
They are also called lenses to support/unload accommodation. They are selected in the same way as distance glasses. The prescription indicates the interpupillary distance for distance separately for each eye and the lens model with the required addition. Mark the frame with the natural position of the head.
These lenses are suitable for anyone who needs distance correction and also has early presbyopia or symptoms of visual fatigue when working at close distances.
Lenses without fixed addition
In essence, these are ordinary progressive lenses that do not have a distance zone. The result is an expansion of the transition and near zones, the ability to accurately calculate the lens power for the middle distance and choose an addition of up to 3.5 diopters. Can be recommended in the same cases as lenses with degression.
Selection is carried out as for progressive glasses. Before writing a prescription, you need to calculate the lens power for the average distance and offer to test the correction. The prescription indicates distance correction, addition (for some models, recalculation may be required using a special formula), distance interpupillary distance separately for each eye, and lens model. Mark the frame with the natural position of the head.
Read more about what recipes are and what they mean in the note.
It is known that after 40 years of age, difficulties appear with focusing vision at close distances - so-called presbyopia, or age-related farsightedness.
At the same time, people who have never worn glasses are forced to purchase plus glasses, patients with hypermetropia (farsightedness) need stronger plus glasses for working at close range, and those suffering from myopia (myopia), on the contrary, use weaker minus glasses for near work than for given.
Presbyopia gradually progresses, reaching its maximum at 60-65 years. Gradually, the range of blurred vision distances will increase, and you may need another pair of glasses for vision at distances of more than 40-50 cm. Some people have 3-4 pairs of glasses for all occasions: for reading, for the computer, for playing billiards , for driving, etc.
The most modern way to correct presbyopia is progressive glasses.
Definition: What are progressive spectacle lenses?
Progressive spectacle lenses are multifocal, i.e. designed for vision at various distances. At the top of the progressive lens there is a zone for distance vision, which the patient uses when looking straight ahead with a natural head position. At the bottom there is a zone for near vision, to use which you need to look down.
The difference in optical power between the distance and near zones is called addition and should not, as in bifocal glasses, exceed 2-3 Diopters, taking into account patient tolerance. The upper and lower zones are connected by the so-called progression corridor, the optical power of which gradually changes (progresses), providing good vision at intermediate distances.
For example, if a person uses glasses +1.5 Dptr for distance, and for near he needs lenses +3.0 Dptr, then the addition is +1.5 Dptr, while the refraction in the progression corridor will gradually increase from +1.5 Dptr at the top to +3.0 Diopter below.
The area connecting the upper and lower zones is called the corridor, since good vision at intermediate distances can be obtained by looking through a narrow area - the “corridor”. The progression corridor is laterally limited by areas that are not intended for vision due to significant optical distortion.
Advantages and disadvantages of progressive lenses
Progressive glasses offer a number of advantages over other types of glasses for the correction of presbyopia.
- With progressive glasses you get excellent vision at various distances, without the need for several pairs of glasses.
- With the same glasses you can view documents, work on a computer, communicate with people, go to the theater, etc.
- Unlike bifocal and trifocal glasses, there is no sharp “jump” in the image when moving your gaze from distant objects to nearby ones, since in progressive lenses the optical power changes gradually.
- Externally, progressive lenses are indistinguishable from monofocal lenses, therefore they look more aesthetically pleasing and will never give away your age compared to bifocals, since in the latter the boundary between the distance and near segments is noticeable from the outside.
- Progressive spectacle lenses can be made from any type of material: glass and plastic, including polycarbonate. Most companies that produce progressive lenses offer a wide range of lenses for various purposes and in different price groups. You can order photochromic glasses with progressive lenses, thin glasses with a high refractive index, aspherical design lenses, etc.
In addition to universal progressive lenses designed for vision at all distances, there are special progressive glasses designed for specific purposes, such as for an office environment or for playing golf. At the same time, the upper zone is designed for a closer distance than in universal lenses, due to this the progression corridor is significantly expanded, which ensures comfortable high vision at the distances required by the user.
With the same glasses you can view documents, work at the computer, communicate with people, go to the theater
Users consider the most significant disadvantage of progressive lenses to be a narrow zone of good vision at intermediate distances and peripheral distortion. It is these features that require some period of adaptation to progressive glasses.
In recent years, there has been continuous improvement in the design of progressive lenses with the goal of increasing the width of the progression corridor with a slower increase in lateral distortion. This makes adaptation much easier.
Beginner users need to get used to always turning their head towards the object in question so that the object “falls” into the progression corridor zone. As a rule, users quickly get used to the peculiarities of wearing progressive glasses and use them just like regular glasses.
Selection of progressive lenses
When selecting progressive glasses, distance vision is checked (or at the required maximum distance), the addition for near is calculated, and the distance from the center of the pupil to the bridge of the nose is necessarily measured for each eye separately (monocular intercenter distance).
Previously, users of progressive glasses were significantly limited in the choice of frames, which had to be wide enough vertically to “accommodate” the progression corridor with the near zone. Progressive lenses of modern design will fit almost any frame you like.
There are individual progressive spectacle lenses, which are manufactured with maximum consideration for the characteristics of the patient and the frame he has chosen. In addition to standard parameters, the following indicators are taken into account: vertex distance (distance from the pupil to the back surface of the spectacle lens), pantoscopic angle (bending angle of the frame plane relative to the face), vertical and horizontal dimensions of the frame, radius of curvature of the frame.
The more accurately the measurements are made, the more comfortable it will be to wear such glasses, and the quality of vision will be high at any distance.
Thus, today, progressive glasses, when properly selected, are the most modern and convenient method for correcting age-related farsightedness.
The first symptoms are deterioration of near vision. Objects blur when viewed closely. A woman has difficulty getting her manicure done. A man goes fishing and there he realizes that he is having difficulty hooking a worm. And at the same time, distant vision did not seem to change. Traditionally, this condition is called “short arm disease” - the vision seems to be good, but the arms are not long enough for clarity at close range. This is for those over 40.
This is presbyopia. With age, a person's vision in terms of ease of focusing at different distances deteriorates. The exact reasons for this “cushioning” of the visual apparatus are still being investigated: it is known, for example, that this mechanism works only in higher primates. Dogs and cats do not have presbyopia, but monkeys do. By the way, this is partly why presbyopia is difficult to study: to study dynamic refraction (accommodation) you need a living object.
The lens thickens and becomes less elastic, the ligamentous apparatus suffers, the muscles lose the ability to function as before - presbyopia occurs. Until recently, the only correct theory of accommodation was recognized by the German physician Helmholtz, put forward in the 19th century, which affects only the lens and its ligamentous apparatus, but more recent studies say that all structures of the eye are involved - the cornea, the vitreous body and even the retina. The result of presbyopia is the loss of the ability to accommodate, that is, the ability to view objects at different distances without additional correction.
When does presbyopia appear?
The average age of onset of symptoms is 40 years, rarely later - I have had patients who felt quite comfortable at 50, but by the age of 60-70 they began to suffer from presbyopia (combined with cataracts). Presbyopia is considered the same natural physiological process as the appearance of wrinkles or gray hair with age.
In my practice, patients have very little idea of what exactly is happening. Almost everyone complains that “I ruined my eyesight with the computer.” No, everything is simpler. You've gotten older.
How does this affect those with nearsightedness, farsightedness or astigmatism? In a person with 100% vision (it doesn’t matter whether it’s natural or after laser correction, or with an implanted intraocular lens), objects nearby begin to blur. The text in front of your nose is not visible either at 8 centimeters, or at 15 - but somewhere further away. To read you need glasses for near vision. Distance vision does not deteriorate. Distance glasses, if any, remain the same.
Myopic people with a slight minus and without pronounced astigmatism can retain the ability to read longer without glasses, although distance glasses will not go away. Moreover, they will interfere when working close, they will need to be removed. The ease of focusing with your previous glasses or contact lenses will disappear. By the age of 50-60, another pair of glasses will appear with a small plus now. In short, plus and minus will not turn into zero.
With stronger myopia, you will need a second pair of glasses, weaker ones, to read and do small work. As a result, by the same 50-60 years, 3 pairs of glasses will appear - the strongest for distance, weaker by 1-1.5 diopters for the average distance and weaker by 2-2.5 for reading and near. In general, there are not many “pluses” in the minus.
Farsighted people feel the symptoms of presbyopia even earlier - after 35 years. This is because they add a plus for accommodation to their advantage. As a result, after wearing reading glasses for a couple of years, they begin to notice that with these glasses they can suddenly see clearly in the distance, but for near visions they require even stronger correction. And such patients run to the ophthalmologist with a story that the computer, or books, or work “ruined” their eyes. And they don’t always believe the story that changes of this kind are irreversible and incurable with drops, miracle pills, strengthening super-exercises, sentences and the urine of a young pig.
As a result, long-sighted people after 40 years of age acquire reading glasses, somehow still retaining the ability to see well into the distance. Somewhere after 50, after an unsuccessful fight against presbyopia, people still wear two or three pairs of glasses or progressive lenses, or seek surgical help.
Astigmats are the worst - their picture quality is poor at all distances. Therefore, the higher the degree of astigmatism, the greater the dependence on glasses. In the end, it all ends with several pairs of glasses.
If you have ever had an eye examination with dilated pupils (before your first glasses prescription, before surgery, during a fundus examination, etc.), the first hour after drug treatment you just get a simplified presbyope simulator. The only difference is that everything around will not seem so unbearably bright.
How does this affect vision correction and laser surgery in youth?
The first case: a patient aged from 18 years (before this the eye is still actively developing) to approximately 40 years old. In this situation, the choice is complete correction. At older ages, in the absence of other problems that may appear by this time (cataracts, glaucoma, retinal dystrophy, etc.), we make allowances for presbyopia.
In any case, after laser correction for emmetropia (a condition when a distant image falls on the retina), any optics becomes close to normal. This transforms a person into a standard presbyopic peer, eliminates the need to wear distance glasses and gives a comfortable feeling in everyday life. And presbyopia should be taken as a given of age.
If you want to reduce your dependence on presbyopia, we find compromise surgical options. There are quite a lot of them, more on this further in the text and in previous posts.
What if I already have presbyopia?
If the patient already has presbyopia and is completely satisfied with several pairs of glasses, then in this situation we say: if you are satisfied with the glasses, this is not a disease. Go ahead and try it. But many are not ready, and really want to make a correction. This is especially true for women - there is a certain stereotype that a woman who puts on reading glasses is already a grandmother (plus glasses are always made with large lenses or, which makes them look even older, they are worn “on the nose”). Athletes and people with an active lifestyle are also willing to undergo correction.
Adjustments are made according to needs. We ask in great detail about the person’s occupation and hobbies. For example, if the patient is a jeweler or embroiderer, a close focus is needed. The patient undergoes examinations with the selected focal length, and he evaluates how comfortable he is. As a result, the optimal method is selected.
Since different tasks require different focal lengths (to simplify, there are three of them: close focus - reading, embroidering, medium distance - computer, music stand, easel, distant focus - driving, theater, etc.), several techniques can be used. I will not write about methods that have been experimentally carried out over the past 20 years - laser and scalpel incisions on the sclera, implantation of rings and accommodating lenses, etc., which have shown their inconsistency. Here are the options:
1. Monovision method. Two eyes are corrected differently: one for near, the other for distance, with a difference of about 1-1.5 diopters. The dominant eye helps you see at a distance, the non-dominant eye helps you see near. Since not every brain can get used to this, tests are necessarily done with glasses or lenses until the patient is convinced that this method is suitable for him. The essence is very simple - you need to learn to switch the driven and leading eyes at different distances of the object. The brain does this automatically.
This method is available for both glasses and contact lenses, phakic intraocular lenses, artificial lenses and laser correction.
This is the principle of monovision.
2. Undercorrection during laser surgery. It’s simple - a patient with vision of -6 diopters receives correction to -1 diopter, and as a result can drive and read relatively comfortably. The type of laser correction does not matter, of course, all things being equal, I am for the SMILE technology as the most progressive and safe. You can read about it in detail.
The method is also available for all types of correction.
3. Laser correction with a presbyopic profile (with multifocal cornea) – PresbyLASIK. Using a laser, you can cut out almost any complex shape with filigree precision, so you can make a lens that will have several focal lengths. The roughest approximation is to apply a Fresnel lens to the eye (although, of course, modern profiles are much, much more complicated). The payback is much more beautiful aberrations. Each laser manufacturing company comes up with its own profiles and methods for creating them. Of course, the market is huge - one hundred percent of patients are their consumers. Therefore, the best minds are working on this.
The bad thing is that in such a situation an irregular cornea is created. That is, it is then more difficult to calculate the artificial lens until we can take these irregularities into account. And in about 5-10 years, you will definitely need a second correction - presbyopia is developing. The patient may feel chromatic distortion, coma. The rays on the retina are focused not into a point, but into a smeared block, or into a star spot.
This is what a multifocal cornea looks like
4. There is another alternative: inserting a special lens with a hole in the center directly into the cornea. In fact, this is the aperture setting. That is, increasing the depth of the sharply displayed space by reducing the amount of light falling on the retina - we leave only those rays that go through the center of the eye lenses. These lenses are not yet certified in Russia. They bet quite actively around the world. The reviews are different, in our German clinic they are not recommended. Among the obvious disadvantages - side optical effects interfere, which are worse in the twilight.
5. Implantation of multifocal phakic lenses. The technique is similar to surgery with refractive phakic IOLs. As a result, the cornea and its own lens are preserved. They do not interfere with the functioning of the eye until the cataract matures. But they are not suitable for everyone in terms of anatomical parameters - the distance between the iris and the lens. The lens grows; not everyone has enough space for an implant in the posterior chamber of the eye. In this case, it is necessary to take into account the width of the patient’s pupils, otherwise aberrations due to multifocal optics may also interfere.
Bottom line - we can't make a presbyopic eye look like a 20-year-old's eye. Any choice is a compromise between picture quality, convenience and the ability to see nearby objects.
What exactly doesn't help?
1. No amount of drops, tablets (even big and red ones), dark rituals or folk methods can correct presbyopia. But obscurantism wins, so people believe in it. And asks for a pill so that everything goes away on its own. Doctors in clinics sometimes cooperate, counting either on the placebo effect or on a pharmacy premium for the drug sales plan. And the Internet is “teeming” with suggestions on how to “change from -5 to 1” without surgery, “read without glasses until old age” and “see through walls”. By the way, often for a lot of money.
2. By exercising the eye muscles, you can slightly improve your vision (in general, it is better to do eye exercises even if you are a healthy person), and partially relieve the effects of fatigue or muscle spasm (as a rule, it does not exist at this age). But nothing can be done with presbyopia systemically. However, you can try working for an hour a day every day. It can't get any worse. Often, in order to avoid wearing glasses for near vision, tricks are used such as illuminating the menu in a restaurant with a mobile phone, buying a phone with larger buttons, enlarging the font on an electronic screen, etc.
To calculate the reserve of accommodative abilities for near, the patient is given a text to read located at a distance of 33 cm from the eyes. Each eye is examined in turn. After this, lenses are placed in front of him: the power of the maximum positive lenses with which reading the text is possible will be the negative part of the relative accommodation. The use of positive lenses causes a decrease in ciliary muscle tension.
The strength of the maximum negative lenses, with which it is still possible to read the text, determines the positive part of the relative accommodation. The use of negative lenses causes additional tension in the ciliary muscles, this part of the accommodation is also called the reserve or positive reserve of relative accommodation. The sum of the positive and negative parts (without taking into account the sign of the lenses) shows the volume of relative accommodation.
As the body ages, the reserve capacity of accommodation gradually decreases. So, according to Donders, in patients with normal vision at 20 years old it is about 10 diopters, at 50 it decreases to 2.5 diopters, and by 55 years old it drops to 1.5 diopters. There are modern devices that automatically measure static refraction and dynamic refraction (accommodation). And we can observe this process “live” during UBM (ultrasound biomicroscopy), where we observe the condition of the lens and its ligaments.
To correct presbyopia, the same optical glasses for near are used. To determine their strength, the formula is used: D=+1/R+(T-30)/10
In it, D is the glass size in diopters, 1/R is the refraction for correcting the patient’s optics (myopia or farsightedness), T is the age in years.
This is what a practical calculation of this indicator looks like for a fifty-year-old patient.
If a person has normal vision, D=0+(50-30)/10, that is, +2 diopters.
For myopia (2 diopters) D=-2+(50-30)/10, that is, 0 diopters.
With farsightedness of 2 diopters, D=+2+(50-30)/10, that is, 4 diopters.
Are you sure this isn't CVS?
Symptoms of computer vision syndrome (CVS) may be similar to those of early presbyopia. Naturally, you need to be seen by an ophthalmologist. However, if you are over 40, there is a 99.9% chance that this is not CVS.
There are several pathological, but temporary changes in accommodation, these include spasm of accommodation. Then we are talking about an abrupt increase in the refraction of the eye, which is associated with the lack of relaxation of the fibers of the ciliary muscle. At the same time, we determine a sharp decrease in visual acuity (especially at distance) and visual performance in general. By the way, this condition can easily be obtained from poisoning with organophosphorus agents and certain medications.
There is also the concept of habitually excessive tension of accommodation - PINA. It causes an increase in the initial refraction of the eye (more often in children), which can progress at different rates. This condition is provoked and maintained by an incorrect mode of visual activity, especially at close range.
Uncorrected farsighted people often have accommodative asthenopia, a condition in which the eye apparatus quickly fatigues during work.
Paralysis of accommodation is accompanied by focusing of the eye on its farthest point. This distance depends on the initial refractive parameters. Paralysis can also occur due to general poisoning of the body (for example, with botulism) and when using certain medications.
And by presbyopia we mean an age-related decrease in accommodative capabilities, characteristic of people over 35-40 years old.
What's next as presbyopia progresses and closer to cataracts? Presbyopia progresses over time, reaching its maximum at the age of 60-70 and eventually developing into cataracts. If opacities appear in the lens, the quality and quantity of vision are noticeably reduced. And the question naturally arises about lens surgery to replace it with a new one. I talked about this in previous posts and.
In short, if the new lens is single-focal, then you will still need glasses for some distance, but if it is multifocal, you will get maximum independence from glasses. Again, you can consider the option of monovision.
The important thing is that in no case should you wait for the cataract to mature and you should part with it when it begins to interfere. The choice of an artificial lens is a strictly individual task, which can only be accomplished by surgeons with extensive knowledge and experience in implanting various IOL models.
