HOW TO PREVENT MYOPIA
Part 1: Proper Close-Work Habits
It should be obvious that there are essentially only two ways to prevent myopia. Either 1) give up all reading and close work, at least until adulthood is reached, or 2) arrange to do the close work in such a manner that the eyes can remain relaxed and focused for distance.
The first of these alternatives is hardly practical, and is becoming even less so as time goes on because of the increasing amounts of close work that our modern society requires.
We obviously must teach our children to read. However, we should abandon the increasingly prevalent practice of teaching children to read even before they start school. Many parents do this without realizing the visual harm they are doing. This just starts the child down the myopia road sooner than necessary. The eyes of preschool children respond very readily to the stress of close work by developing myopia. In addition, the child will be reading for a greater number of years before reaching adulthood, and there is thus more time for a greater amount of myopia to develop. Age six is early enough to start teaching children to read.
Many children spend over three-fourths of their working hours concentrating on things at close range. This is a totally unnatural use of the eyes.
This leaves us with the second alternative, and there are a number of things which can be done in this area. We will deal first with the more simple methods that do not require use of preventive aids or mechanical devices.
When reading, the child should look up and into the distance momentarily at the end of each paragraph, or at least at the end of each page, to relax the eyes. Ideally, the chair should be placed to enable looking out a window or across the room when looking up.
If a book is lying on the desk in front of a child, the top of the book is obviously further from the eyes than the bottom of the book. This means that as the child reads down the page an increasing amount of accommodation will be required. If the book is lying flat on the table, as much as 3 D more of accommodation will be needed to read the bottom of the page than is needed to read the top. It is better to support the book on a slant board so that the pages are more perpendicular to the line of sight and the bottom of the book is farther away (See figure 1). The angle between table and book should be fifty or sixty degrees. It is possible to make or buy an elevating desk with a surface that can be raised to various angles and locked in position for this purpose.
When a conventional desk is used (or when an elevating desk is in the horizontal position for writing), it is important that the desk surface not be too high for the child. This unavoidably puts the work too close to the eyes. Raising the chair is one way of overcoming this problem.
Some people feel that small print in books contributes to the development of myopia but this is not really true. Only if the book is held closer to the eyes than it would otherwise be (because the small print is harder to see) can it be said that small print contributes to the myopia. For this reason, the print in children's books should be large enough that the child does not need to hold the book too close. Small print can be boring and tiring to the eyes but it does not cause myopia. It is the distance from the eyes to the book which is of most importance.
The elbows should not be rested on the desk or table when reading or writing since this creates a posture which usually causes the head to bend forward too close to the work.
A child who habitually reads while lying on the left side will probably develop more myopia in the left eye than in the right eye, because the left eye is closer to the book. If the right side is used, the right eye will probably develop more myopia.
It is the job of the schools as well as the parents to teach proper reading posture and proper reading distance to the children. Teachers should remind their pupils daily about the proper use of the eyes and proper posture. At present, this valuable information and training is being universally ignored.
Good lighting causes the pupil of the eye to become smaller, requiring less accommodation, as was explained in an earlier chapter. In addition, good lighting eliminates the need to hold the book close.
The indiscriminate use of sunglasses or tinted lenses of any kind should be avoided for the same reason, at least when doing close work.
It is possible that the eyes somehow become temporarily weakened so that they more easily become myopic from excessive close work. Or, it may merely be that too much close work is being done in a darkened environment. In any case, if close work is prohibited when a child is ill, there will be little risk of myopia developing. Watching television should be encouraged in preference to reading.
While the proper close-work habits described above are beneficial, they are seldom sufficient to prevent or halt myopia in children who have the tendency to develop it. The amount of close work done by children in our modern society is just too much to be counteracted by any halfway measures. More strenuous measures are nearly always needed in order to prevent accommodation to a greater extent and for longer periods of time.
Part 2: Preventive Aids
Preventive aids are used to reduce or eliminate accommodation when doing close work and they fall into several categories:
Suppose that the book is normally held at about a distance of one-third meter from the eyes, at B. Since a +3 D lens has a focal length of one-third meter, if it is placed in front of the eye it will make the diverging rays become parallel before entering the eye. The dotted lines show that the eye is receiving parallel rays as if from a distant object. Thus, this eye can read without accommodation. This is called reading at the far point.
To better understand this idea, imagine that you wish to take a picture of a close object using a camera that is focused for infinity. You could do this and still get a clear picture if you place a plus lens of appropriate power in front of the camera lens. We are doing something similar with the eyes.
Now suppose that the book is pushed just a little farther away from the eyes so that it becomes a little blurred. Figure 3 shows this situation.
Now the eye is receiving converging rays, something which does not normally occur in everyday life. Only optical lenses make this possible. Notice that the lens of the eye is fully relaxed and cannot relax further. The rays are therefore bent too much and come to a focus slightly in front of the retina. The result is a slightly blurred image. This is called the blurred image or fogging technique because it purposely makes the vision a little blurred or foggy. This technique is especially useful in relaxing a ciliary spasm that is already present. However, in dealing with an eye that is already myopic, the true situation would be like figure 4 rather than figure 3.
Figure 4 represents an eye that is already rather myopic so that even in its totally relaxed condition it requires diverging rays to see clearly. If the eye is 1 D myopic, this means that it has + 1 D more refractive power than it should have. Therefore, an additional +2 D lens is all that is needed to give a total power of +3 D and completely relax the eye for a one-third-meter reading distance.
The above reasoning can be expressed in tabular form as follows:
|Distance Prescription||Reading Glass Lens Needed to Totally Eliminate Accommodation at 1/3 Meter Reading Distance|
|-1 D||+2 D|
|-2 D||+1 D|
|-4 D||-1 D|
|-5 D||-2 D|
|-6 D||-3 D|
The appropriate lens for each eye is selected individually since the two eyes do not always have the same refractive error. However, if the eyes are not too different in refractive power, the same eyeglass lens power can be used for each eye without difficulty. A special prescription for reading purposes is frequently called an add since the distance prescription is used as the starting point and the prescription for the reading glasses is added to it. To illustrate, if a person uses -5 D lenses for distance and has a +2 D add for reading, the reading prescription is -3 D.
This terminology is most commonly used with bifocals (see below) where the lower segment is the add. However, the same terminology can be used if the add is a separate pair of reading glasses.
The use of the fogging technique creates an active relaxation of the ciliary muscle and thus has a greater effect on relaxing a ciliary spasm than could be accomplished by merely eliminating the accommodation (with no fogging). The reason for this is that the ciliary muscle is composed of two separate sets of fibers. The circular fibers are obviously used to tighten the muscle and increase the accommodation. The radial fibers are used by the eye to relax the muscle and decrease the accommodation. This has been given the term negative accommodation.
Thus, the fogging technique forces the ciliary spasm to relax, as the eyes attempt to see the blurred image clearly. However, most doctors who prescribe reading glasses do not give an add that will eliminate all of the accommodation. They may prescribe an add of only +1 D, +1.5 D, or +2 D. The reason for this is that many children have difficulty "accepting" a large add. That is, the add causes some "side effects" in the form of various vision problems.
This drawback of reading glasses is due to the fact that there is a strong linkage in the human visual system between accommodation and convergence (turning the eyes inward when looking at something close). As a viewed object approaches the eyes, accommodation and convergence increase in proportion to each other. Over thousands of years, the brain has learned that this is the normal situation. Consequently, accommodation stimulates convergence and vice versa. Thus, if we converge without accommodating the appropriate amount, or if we accommodate without converging the appropriate amount, problems can develop.
This close relationship between accommodation and convergence is upset when reading glasses are used to eliminate the accommodation for reading. Since the eyes must still converge on the book, an unnatural situation is created. The result can be eye fatigue, double vision, or other types of fusion problems. That is, the two images can no longer be fused together without discomfort. Normal binocular vision is interfered with. For this reason, the book should be held as far as possible from the eyes to reduce the amount of convergence needed.
This problem can also be partially overcome by prescribing a prismatic component in the reading glasses to reduce the amount of convergence required. Figure 5 shows how this is done.
These prisms are placed with the bases toward the nose and are called base-in prisms. In figure 5, the plus lens and the prism are shown separately. In reality they are made as one lens.
However, using prisms as described above to totally eliminate convergence will cause severe distortion due to the thickness and shape of the lenses, and is not done.
Reading glasses can also be made in a half-eye form in which it is possible to look over the top of the lenses for distance vision rather than having to remove the glasses.
The reading glasses with plus lenses that have been described are the same type of glasses that usually become necessary for people after they reach their forties. Because of changes in the eyes with increasing age, the eyes can no longer accommodate sufficiently for reading. Therefore, plus lenses are used by older people because they can't accommodate; on children, plus lenses are used to avoid accommodation. Reading glasses can be purchased cheaply in many retail outlets. However, such reading glasses are intended for adult-size heads. The distance between the lens centers conforms to the usual distance between the pupils of adult eyes, around 60mm when reading. If such glasses are used by young children, who have a smaller interpupillary distance, the "prismatic effect" of the lenses causes increased convergence. This can cause problems such as double vision and should be avoided. The optical centers of the lenses should be no further apart than the child's interpupillary distance when reading.
Reading glasses can be provided in a bifocal form, with the upper segment used for distance and the lower segment used for reading. In this manner, the schoolchild can look up at the blackboard without having to remove the glasses. The statements made above about upsetting the accommodation/convergence relationship also apply here when looking through the lower segment. The success of bifocals has been shown in a very interesting and significant study prepared by Francis Young and Kenneth Oakley.1
Dr. Oakley earned degrees in both optometry and ophthalmology and, until his retirement, had a practice in Bend, Oregon. For many years he urged the parents of his young nearsighted patients to permit the use of bifocals to try to slow or stop the progress of the myopia. This study is entitled "Bifocal Control of Myopia", and it compares those children who wore bifocals with those children who did not. The procedure was as follows:
When the initial refraction (eye examination) indicated that the child was in or close to myopia, a bifocal was prescribed with an upper segment containing a slight undercorrection (about 0.5 D) for distance, and with a lower segment containing an add of about +1.50 D for reading. If the parents did not wish to try the bifocal approach, the child was fitted with a slight undercorrection (about 0.5 D) and told to wear the glasses at all times. These children thus formed the control group.
Oakley's practice consisted of both Caucasian families and Native American families. Because of differences in reading habits, life style, etc., the results for the two groups were tabulated separately. The children were between six and fifteen years old and their refractive error was recorded over several years. The results of the study are shown below:
|Group||Rate of myopia increase/year|
|Native American Control Group||0.37 D|
|Native American Bifocal Group||0.11 D|
|Caucasian Control Group||0.52 D|
|Caucasian Bifocal Group||0.025 D|
The annual rate of increase for the Native Americans is more than three times higher for the control group than for the bifocal group. Among the Caucasians, the annual rate of increase is twenty times higher for the control group than for the bifocal group.
The wide difference between Native Americans and Caucasians in this study is discussed by the authors at the conclusion of their paper:
The Native American subjects generally read less and less intensively than the Caucasian subjects. They also tend to drop out of school earlier and do not wear their bifocals as compulsively as do the Caucasian subjects. Since the Native American bifocal wearers do not use their bifocals as consistently as the Caucasian subjects, the bifocals should be less effective, which they apparently are. On the other hand, since the Native American subjects do less reading, the control subjects should show lower rates of progression, which they do. Thus, the reading variable alone could account for the differences found between the two groups. Since even under these conditions the bifocals seem to have a significant effect on the annual rates of progression and clearly have a significant effect on the Caucasian subjects who follow the instructions better and also do more reading, the bifocals seem to be a relatively effective means of controlling the progression of myopia.
This report, as is customary in research reports, is written in conservative language with the use of expressions like "our research would suggest" or "these results tend to indicate," and consequently the layperson might tend to underestimate the great importance of what has been proven in this study. Here is a method which can reduce the rate of myopia progression to a fraction of what it would otherwise be.
One reason given by the researchers for the success of this method is that the lower segment of the bifocal was fit quite high so that the child could not look over it when reading. The top edge of the lower segment was placed at the same level as the lower half of the pupil. Some studies done in the past by other researchers have not shown such good results, possibly because the reading segment was fit too low. The reading segment should also extend all the way across the lens so that the child cannot look around it and the child should be observed to be sure that the bifocal is being used properly.
Figure 6 shows a bifocal of a type that is suitable for this use. Some parents object to the use of a bifocal on their children because they associate bifocals with elderly people. It is important to overcome this misplaced vanity and lack of understanding when the preservation of vision is at stake. A child wearing a myopia prevention bifocal shows that the parents have an advanced understanding of the myopia problem.
Another form of multifocal lens is the progressive lens. While an ordinary bifocal lens has a sharp dividing line between the upper and lower segments, a progressive multifocal lens has no such line. The power of the lens changes gradually from top to bottom. Some specialists prefer eyeglasses of this type to bifocals.
These techniques are limited in what they can accomplish in preventing myopia. In fact, pinhole glasses can do much the same thing at far lower cost. And the Myopter can not only prevent myopia but reduce myopia that is already present. Read further to learn about these amazing preventive aids.