Sensory anomalies in strabismus.

In cases of concomitant strabismus of childhood onset, areas of suppression develop in the visual field of the deviating eye in binocular vision (see this subject reviewed by DuBoisPoulsen, 1952; Mackensen, 1959; Ravalico, 197 I). There also develops in binocular vision, a variation of the directional localization of the retinal elements of the deviating eye which is called "anomalous retinal correspondence". A certain degree of binocular vision may be acquired if this anomalous correspondence is "harmonious". This "harmony" in fact, indicates that an extrafoveal retinal area in the deviating eye, where the image fixed by the fixing eye is formed, has acquired the same directional localization as the fovea of the fixing eye. Recent studies (Bagolini I96I-I967) have demonstrated that suppression prevails in cases of large-angle strabismus, while in cases of small-angle deviation, anomalous correspondence of the harmonious type tends to prevail. This latter mechanism has very probably a true antidiplopic effect because the two retinal images may be superimposed in spite of the fact that they stimulate originally non-corresponding retinal areas. It has also been demonstrated that, in cases of harmonious anomalous correspondence, a type of anomalous binocular vision may be achieved with the development of areas of binocular vision bearing close resemblance to Panum's areas in normal subjects (pseudoPanum's areas). This type of binocular vision remains, however, quite weak in comparison to normal binocular vision so that it can be demonstrated only with tests (such as the striated glasses test*) which do not alter casual seeing conditions. Other tests which do alter casual seeing conditions, usually by making the two retinal images unequal, easily disrupt this weak state of binocularity (the so-called dissociating tests). It has also been demonstrated that, after surgical correction ofa large angle ofstrabismus, a sensory reorientation of the retinal elements in the deviating eye may occur quite rapidly (Bagolini, I967). A new harmonious retinal correspondence then develops which is adapted to the smaller residual angle of deviation. If we succeed in completely eliminating the strabismic deviation, correspondence rapidly becomes normal with the striated glasses test. With the more dissociating tests, correspondence may eventually become normal if we succeed in keeping the eye straight for a sufficiently long period of time. It is because of these new findings on the postoperative behaviour of retinal correspondence that prism therapy has been revived. Prisms, in fact, have been used for a long time in strabismus, but the idea of treating sensory anomalies with prisms is rather recent (Bagolini, I962). This approach, which I have applied only to convergent strabismus, appeared only rarely to be successful. This is because the optical elimination of a residual convergent strabismus by means of base-out prisms tends to elicit an increase in the deviation which frequently compensates for the prismatic correction. These convergent movements are an