Most of what we know about treating occasional squinters with anomalous correspondence comes from experience with exotropes where this combination of conditions is fairly common. When treating occasional squinters with anomalous correspondence it is important to recall that when these patients are not squinting (fusing) they have normal retinal correspondence (zero angle of anomaly). The anomalous correspondence that manifests itself when the strabismus is present becomes normal as fusional vergence is exercised to straighten the eyes. This "co-variation" between fusional vergence and the angle of anomaly (Hallden, 1952) forms the basis for treating this type of strabismus. Specifically, treatment is directed at enhancing the already- present fusional vergence which allows the squint and the anomalous correspondence to be overcome simultaneously.
About half of these exotropes will have significant refractive errors --- about 25% have bilateral myopia and another 25% have myopic anisometropia. Correcting the refractive error of these patients produces results much like that for occasional squinters with normal correspondence, that is correcting seemingly trivial refractive errors produces substantial increases in the frequency of fusion.
Added lenses are useful for some of these patients but they do not produce the straight-forward results that occur in occasional squinters with normal correspondence. Added lenses change accommodative vergence, but this vergence never or rarely (Kerr, 19__; Daum, 198_) produces associated changes in the angle of anomaly. When added minus lenses, for example, are applied clinically to occasional exotropes with anomalous correspondence, small amounts seem to facilitate fusional vergence and enhance bifixation with correspondence becoming normal. Larger added lens powers seem to interfere with co-variation and can result in bifixation with diplopia or in blurred vision from a lack of accommodative response to the added lenses. Cavalier use of added lenses for occasional squinters with anomalous correspondence should be avoided, and judicious use should be encouraged.
As with added lenses, horizontal prisms can be troublesome for occasional squinters with anomalous correspondence. Giving base-in prisms to an intermittent exotrope with anomalous correspondence, for example, will probably result in the eyes diverging to the prisms in order for the retinal images to continue to fall on (anomalously) corresponding retinal points. Prisms need to be considered early in treating these patients principally to neutralize an existing vertical deviation that may be impairing fusion. Usually, but not always, anomalous correspondence does not seem to be present vertically in occasional squinters; thus, vertical prisms are effective in neutralizing a vertical deviation and enhancing fusion in these patients
Since occasional exotropes usually do not have much amblyopia, treatment of the amblyopia can usually be accomplished with occasional occlusion. This passive treatment can be facilitated by anti-suppression training --- but there is typically little if any suppression coexisting with the anomalous correspondence.
Anti-suppression orthoptics for these patients is usually needed only to break down small areas of central suppression, but NOT to create diplopia (when the eyes deviate) as a stimulus to fusion as is done for occasional squinters with normal correspondence.
As pointed out earlier, motor fusion training gets the eyes straight and when accomplished, correspondence becomes normal. The challenge is how to train fusional vergence when diplopia cannot be used as a stimulus for fusional vergence when the eyes are deviated --- since the anomalous correspondence with the eyes deviated prevents diplopia. Occasional exotropes with anomalous correspondence can be trained to sense when the eye deviates (sometimes through the increased visual panorama) and to straighten the eye by executing a reflex fusional vergence movement. Training facility of fusional vergence and the sensory aspects of fusion (such as stereopsis) helps these patients develop the necessary reflex fusional vergence.
Surgery for these patients is not usually necessary unless the angle of deviation is large or there is discomfort. It is not clear what effect anomalous correspondence has on the outcome of surgery. Germane to this issue is a report by Flom et al. (1978) on an intermittent exotrope with anomalous correspondence wherein measures of retinal correspondence were made before and immediately after surgery, as well as considerably postsurgically. Their patient had intermittent exotrope of 54 p.d. with harmonious anomalous correspondence; six hours after surgery the angle of anomaly shifted abruptly by as much as 54 p.d. with some fluctuations; ultimately the angle was 3 p.d. exophoria with an angle of anomaly of -3 p.d. (harmonious). Clearly, correspondence can change postsurgically quickly and in ways unassociated with covariation; prompt evaluation of the postsurgical status can help in determining the need for additional surgical management (including adjusting the original suture) or in giving postsurgical vision training or optics.