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What Causes Eye Strain?
When we read or do close work our eyes must do two things: aim or converge accurately, and focus or clear the image (accommodation). Think of a camera you must aim the camera and focus the image. In this case either cameras or eyes have to work easily, and efficiently together. Our eyes were never designed to spend long periods of time staring at computer screens or reading books. Our eyes were designed to constantly change fixation, looking near and far.
Thus, it is not surprising that many of us develop a form of cramping while looking at close work. This form of cramping is called eyestrain; the technical term is asthenopia. Patients complain of aching or pulling of their eyes, headaches, fatigue, falling asleep while reading, and loss of concentration. After reading distance objects appear blurred for a couple of minutes. The precursor to near-sightness or myopia. The symptoms are like a chronic back-ache, most patients learn to live with them; some never telling the eye doctor they have them. The symptoms tend to get worse during the difficult years of high school, college, professional school or during work. They may interfere with work or learning.
Can You Prescribe Glasses to Eliminate My Eye Strain?
In a few cases glasses will work to relieve eye-strain but in the majority of cases they will not work. Remember, glasses improve the clarity of an image and most eye-strain muscle problems have little to do with clarity. Thus, glasses are for seeing problems and exercises are for muscle problems. Sometimes glasses can be prescribed to relieve a portion of the eyestrain. The prescription either reduces the accommodative (focusing) demand and/or muscle problems that produce eye-strain. The problem with glasses is that the patient may adapt to the them making them less effective over time.
Exercises or vision therapy is designed to eliminate the problem. It is designed to develop the appropriate reflex, thus, eliminating the effort used while reading or performing computer work.
Can I Do the Exercises at Home?
You can thing of exercises for the eyes like working out. If you are like most of us, the ability to carry out a structured program at home is not so good. Therapy at home can be though of as three different levels, similar to doing exercises: pencil push-ups, computerized, and intensive structured office. Pencil push up is analogous to jogging, home therapy to a home gym, and office based therapy to gym with your own personnel trainer. Which one do you thing is going to be more effective? While push ups will work for a few, office based therapy almost always works when done with re-enforcing home therapy.
If I Do the Exercises, Will I have to do this for the Rest of My Life?
No. Though we described the problems as if they are a pure muscle strength problems, they are not. For one reason or another you or your child never learned or developed the reflex to properly accommodative (focus) or converge the eyes. Therapy teaches the reflex. A similar analogy is learning to ski or to play a piano. While learning either skill our muscles hurt and we suffer generalized fatigue. When you learn to ski or play a piano properly, they are performed without effort and the reflex stays with you.
Is This the Same As Strabismus?
When the muscles work together but inefficiently eye-strain, diplopia (double vision), and fatigue ensues. The eyes are working together but poorly. When the eyes give up, an eye turn develops – this is known as strabismus. If the strabismus initially occurred at a young age, the child suppresses an eye, thus, no conflict, no eyestrain, nor double vision. Most patients with strabismus, unless intermittent, do not have symptoms of eyestrain.
What are some of the Common Muscle Conditions That Cause Eyestrain?
Convergence insufficiency This is the most common eye muscle disorder. It is present in approximately 4% of the population. It is characterized by an inability to converge or look close for long periods of time. Often the patient has a tendency for one of the eyes to drift outward while reading or doing close work. Sometimes the eye actually drifts with resultant double vision. The effort to keep the eyes working together results in eye-strain, fatigue, car sickness, headaches, double vision, blur, loss of concentration, etc. Treatment with vision therapy is successful in over 90% of the cases. Glasses can sometimes be used in this condition.
Convergence excess The eyes have a tendency to point too close at near (over-converge). This eye muscle problem is easily treated with either reading glasses or vision therapy.
Divergence insufficiency Uncommon eye muscle problem in which there is a tendency for the eyes to turn inward at distance. Toughest case. Hard to teach divergence (turning out of the eyes), may utilize prism, surgery (not very effective)
Divergence excess Tendency for the eyes to turn outward at a distance. Rarely causes eye-strain. Usually breaks down into a strabismus. Effectively handled with vision therapy. Surgery is sometimes necessary. See intermittent exotropia under strabismus or publication.
Esophoria Eyes tend to over-converge at distance and near. If the tendency is not too large vision therapy is effective. If too large of a tendency to turn, surgery may supplement therapy.
Exophoria Eyes tend to under-converge at distance and near. Similar symptoms and treatment as convergence insufficiency. Treatment success is very high.
Accommodative insufficiency Inability to sustain focusing or accommodation. Patients complain of blur or eyestrain at near after reading or doing close work. Treated with reading glasses or vision therapy. Vision therapy provides a cure and more effective remediation of symptoms.
Accommodative inertia Inability to make rapid shifts or changes in accommodation. Patients complain of blur upon looking up, or more uncommonly blur when looking from far to near. The first sign of myopia.
Hyperphoria Tendency for the eyes to turn upwards. Often times one is born with this problem. However, symptoms do not occur until high school or later. Prismatic glasses may be prescribed, however, many patients adapt or “eat up the prism”, requiring frequent increases in the amount of prism needed to correct the problem. Vision therapy is usually very successful in stabilizing the muscle problem.