Differences in size between the retinal images of the eyes may arise in asymmetric convergence because the object fixated will be at a different distance from the two eyes.1 The magnitude of the difference will obviously increase with the nearness of the object and with the degree of the lateral turning of the eyes. In the normal use of the eyes when looking sideways at near objects, retinal images of objects subtending unequal visual angles to the two eyes are fused into a single composite image. No apparent difficulties arise in this act.
Difficulties may arise, however, when it is necessary to fuse images of unequal size produced artificially with size or power lenses or when patterns of unequal size are presented in the stereoscope. Fusion may not then be possible if the difference in size is outside fusional areas (so-called Panum's areas of sensation2). However, apart from
OGLE KN. RELATIVE SIZES OF OCULAR IMAGES OF THE TWO EYES IN ASYMMETRIC CONVERGENCE. Arch Ophthalmol. 1939;22(6):1046–1067. doi:10.1001/archopht.1939.00860120118008
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