A Contrast in National Techniques for the Clinical Investigation of Visual Dysfunction

Abstract

Summary 1 The success claimed from the use of the Infinity Balance test would, upon close analysis of the principles underlying its design and application, suppose and/or depend upon the existence predominantly of refractive anomalies, imperfections arising out of the usual monocular methods for estimating the ametropic correction, and errors of binocular balance, in the scheme of functional visual disorder.2 By simultaneous binocular parallax and alternate monocular macular fixation of separate test objects, the Infinity Balance test facilitates the visual balancing and adjustment of the ametropic correction necessary to permit both comfortable binocular vision and the efficient performance of the prescription. It helps to detect the presence of lateral and vertical imbalances opposing binocular equilibrium.3 Infinity Balance viewing under the conditions imposed by the intervention of a septum dividing the central field of binocular vision affords the detection of abnormal suspension or suppression. In this connection its extension to orthoptics for the reeducation of simultaneous vision must be approached with caution. Simultaneous perception under this test involves the macular image of the test object engaging the fixation of one eye and the extra‐macular image of the other test object for the other eye. Each eye alternates between macular and extra‐macular image representation as fixation is divided between the two eyes for viewing and assessing the visual quality of the laterally separated test objects. In cases of abnormal retinal correspondence the continued application of Infinity Balance viewing under these conditions serves only to consolidate anomalous correspondence at a stage where simultaneous (contemporaneously) foveal stimulation and macular perception are necessary for the rehabilitation of normal correspondence and fusion censolidation upon this alliance. As a precursor only, to the re‐education of simultaneous macular perception, Infinity Balance viewing may well prove an invaluable techníque both as a method for the breaking down of abnormal suspension or suppression and establishing simultaneous vision. Its later application to stereoscopic viewing is another usefui adaption of its clinical use.4 Aniseikonia and its measurement has been discussed in the light of perceptual ocular image difference. It is a condition affecting binocular vision and is measured under carefully‐controlled binocular conditions which reveal relative ocular image differences. Anomalous incongruity of the ocular images is known to effect disturbance of binocular spatial perception and orientation, and hinder the normal processes of binocular vision. The correction of anisometropia may introduce image differences which render binocular vision uncomfortable. There is no essential, concomitant, or linear relationship between anisometropia and aniseikonia. Aniseikonia can exist where there is no anisometropia, or in emmetropia. Because it is not known whether the ametropia is axial or refractive in a case of anisometropia, the amount of aniseikonia cannot he predicted, hut has to he determined by measurement.5 The evidence available reveals that aniseikonia may well he the potent and initial source of conflict encouraging and contributing to the development of conditions, a number of which we may see manifested under Infinity Balance viewing, e.g., abnormal suspension or suppression, binocular imbalance, imperfections of the unilaterally estimated ametropic correction, etc. In this connection eikonometric procedure is more introspective than Infinity Balance procedure as a diagnostic probe, and further for its special ability to screen anomalous image incongruities which affect hinocular vision. The Infinity Balance test is not a reliable screening test for the various forms of anomalous ocular image difference.A comparison can be made, but the sensitivity would he poor and, moreover, fail to detect the meridional differences. Large differences can, of course, be detected by rapid monocular comparison, e.g., corrected unilateral athakia. An estimation of aniseikcnia with any precision, using the Infinity Balance Test, would be difficult and the method of evaluation uncertain.