by Leo Anghart
The science of convergence
Numerous clinical studies report on the efficacy of Vision Training for convergence insufficiency. Cooper and Duckman (1978) reviewed 15 studies of Vision Training for convergence insufficiency over a 47 year period. These studies surveyed nearly 2,000 patients and reported an overall cure rate of 72 percent, with improvement in an additional 19 percent, and failure in only 9 percent of cases.
Impressive cure rates are reported by Duthie and Mayou (1945), who achieved cures in 72 percent of 364 patients with convergence insufficiency.
The science of strabismus
Usually strabismus is managed by means of prism lenses or corrected by surgically weakening or tightening the eye muscles. Often there is immense pressure placed on parents to give permission for their children to undergo surgery. However, the result of strabismus surgery is not impressive. In many cases it is only a cosmetic procedure which fails to achieve stereoscopic vision.
Efficacy of the non-surgical Vision Training approach
Wick (1987) did a retrospective examination of the records of 54 patients who had undergone vision treatment for accommodative esotropia (the eye turning inwards). The patients were classified based on the Duane classification as having either convergence excess (n = 11) or equal eso-diversions (n = 43).
Over 90 percent of the patients achieved total restoration of normal binocular function with this treatment approach.
Chryssanthou (1974) studied 27 patients with intermittent exotropia (one eye turned out) with ages ranging from 5 to 33 years of age. A total of 89 percent of patients showed definite improvement, with 66.6 percent graded excellent six months to two-and-a-half years after treatment.
Etting (1978) reported a 65 percent overall success rate in patients with constant strabismus, specifically, 57 percent for esotropes (eye turning in) and 82 percent for exotropes (eye turning out). There was an impressive 89 percent success rate with intermittent strabismus, specifically, 100 percent of esotropes (eye turning in) and 85 percent of exotropes (eye turning out). Etting reported an astonishing 91 percent success rate when retinal correspondence was normal.
Flax and Duckman (1978) examined the effectiveness of orthoptics as a viable modality for treating strabismus. They reviewed the pertinent literature and presented an analysis of the data. The result of numerous studies showed a combined functional cure rate of 74 percent. Ludlam (1961) evaluated the efficacy of orthoptic strabismus treatment in a selected group of 149 selected strabismus sufferers who received Vision Training treatment, and determined a 73 percent overall success rate.
In a subsequent study Ludlam and Kleinman (1965) found the long-term success rate of vision therapy for strabismus to be 65 percent. Bryer (1961) investigated the long-term effects of treatment of heterophoria. Of 89 patients whose initial symptoms were completely relieved during treatment, 81 percent remained symptom free on follow-up six to ten years after treatment. Only 4 percent experienced a recurrence of symptoms severe enough to require further treatment. Also Vaegan (1979) reported successful results with isometric training in a 1979 study.
Many of the above studies may seem dated. However, the strabismic condition remains unchanged through time and the efficacy is thus still relevant and important.
The science of amblyopia
So far researchers have no understanding of the underlying causes of amblyopia. When amblyopia is associated with strabismus it is believed that the conflicting input from the two eyes results in active suppression and amblyopia of the nondominant eye. Amblyopia may also be the result of stimulus deprivation caused by cataracts or by large hypermetropic errors.
Many researchers concentrate on the treatment and management of amblyopia. The prevailing belief is that the best possible vision in an amblyopic eye is obtained when the normal eye is prevented from seeing. Pugh (1954) found that vision decreases when both eyes are open, indicating that the normal eye has an inhibitory effect on the amblyopic eye. In a 1966 study, von Noorden and Leffler demonstrated that the greater the luminances of the stimulus to the normal eye the lower the vision in the amblyopic eye.
In some cases the normal eye becomes amblyopic after wearing patches. Ikeda (1980) demonstrated that stimulus deprivation of amblyopia could result from the use of atropine or penalization (wearing eye-patches).
Patching or penalizing the good eye was first recommended by de Buffon in 1743. This is still the preferred method of treatment by doctors to this day. Over the years attempts have been made to supplement this passive treatment with active stimulation of the eye. Electrical and chemical stimulation has been tried without much success.
The various strategies used are:
• Total occlusion, excluding all light and form. An example of this is placing adhesive occluders over the eyes. In some cases black contact lenses have been used.
• Total occlusion, excluding form but allowing some light. Examples of the treatment would be wearing frosted glasses or other filters.
• Partial occlusion, allowing the appreciation of form but diminishing its acuity. An example of this would be to cover only part of the eye. This partial occlusion is widely used in France. Another example is blocking the lower half of the lens to promote the use of the amblyopic eye for close work.
• Optical penalization uses lenses to blur the vision of the better eye in order to force the amblyopic eye to work.
• Cycloplegic drugs are used to blur the vision of the good eye. The drug commonly used is atropine as drops or ointment.
The prevailing medical approach is to force the amblyopic eye to work by blocking the vision of the good eye. Forcing small children to wear patches and in some cases actually restraining them by blocking elbow movements is fortunately becoming unacceptable to parents.
Causing the vision of the good eye to blur is also a questionable approach since it is well known that wearing lenses causes the eye to adjust to the lens worn. In this case the otherwise normal eye will be forced to lower its visual acuity as demonstrated by Ikeda and Tremain’s (1978) research.
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