but without symptoms, and that there are remediated CIs who still present symptoms. She concludes that since there is no correlation between signs and symptoms, CI must be psychogenic in nature. In the authors opinions this is a naive approach since no one has yet evaluate the relationship of suppression amount of effort, amount of near work, etc., with the manifestation of CI. Therefore, it would appear there is little evidence available to support the theory that CI patients with symptoms are neurotic. However, the authors have observed that “neurotic” patients often manifest symptoms to a greater degree than “non-neurotic” patients.

Another theory is developmental in nature.’⁹ It is based on the premise that there are two types of convergence movements. One is an unconditioned reflex originating in the occipital lobe and responding to disparity or fusion. The other is a conditioned reflex and originates in the frontal lobe. The corrective eye movement for the fusional reflex develops through experience by age five. Prior to this age accommodative convergence, voluntary convergence, and fusional convergence have not had enough experience to stimulate the psycho-optical reflex of convergence. Therefore, a lag in usage or in development will cause a convergence insufficiency. The difficulty with this theory is that with more sophisticated sensory testing with infants, it can be demonstrated that stereopsis, adequate visual acuity and convergence are all present within a few months after birth.

Most CIs present themselve⁵ without a known systemic or psychological cause. The CI may result from a breakdown of accommodative convergence, fusional convergence and/or voluntary convergence. It would 

 

seem that this breakdown would result in ocular fatigue with sustained near work. However, since the system is involuntary and the muscles are much stronger than they need to be to converge the eyes, there should theoretically be no ocular fatigue. However, there is!

The authors feel that the breakdown in binocular vision is the result of a combination of factors and that these are the cause of ocular fatigue. Firstly, during near point tasks the eyes must maintain a constant and delicate balance between accommodation and convergence while performing close work. Secondly, accommodation and convergence are required to maintain a static position during near work.  Thirdly, retinal disparity cues are absent during reading, making it more difficult for the eyes to maintain fusion. These three factors, in combination may explain the ocular fatigue CIs experience if convergence is weak.

Treatment

Almost 95% of the authorities cited in this paper state that CIs respond well to visual training or orthoptics, i.e., symptoms diminish and objective clinical findings improve. Table 1 lists the studies done to date.

Table 1 clearly illustrates the success with which CI can be remediated through vision training and orthoptics. These highly consistent findings are somewhat surprising in view of differences in treatment, differences in definition of CI, differences in skills and motivation of. therapists that exist between investigators. Most treatment programs were relatively short (5 - 11 visits) and therapists concentrated on building fusional, voluntary, and accommodative convergences. Some therapists used anti-

suppression techniques, while others stressed jump ductions. Despite differences in therapy programs, 94% of patients treated showed relief of symptoms. Stutterheim⁵¹ and Mann,’⁹ have demonstrated improvements in visual acuity as a function of the elimination of small central suppressions. Many treated patients report improved concentration and retention. Passmore and MacLean⁸ noted that general tension disappeared and that their patients showed a positive change in personality. Another study reports that migraine headaches often ceased at the end of treatment of CI ^11,48

Mellick³⁵ compared the results of treatment of CI between normals and diagnosed neurotics. He found 77% of his “neurotics” cured, 8% improved, and 14% without change. In the normal group, 78% were cured, 15% improved and 5% showed no improvement as a result of treatment. He concluded that there was no significant difference between groups.

The authors feel that treatment results may be enhanced by the use of monocular and binocular accommodative flexibility training, BO and B! range extension, jump ductions, voluntary convergence and sustaining of convergence or divergence while doing extended periods of near work, e.g. prism reader.

The authors have developed a training regimen ‘for the treat-