Handbook of ophthalmology . explain almost all cases of pathological diplopia,upon the basis of the so-called empirical theory of vision. If wefix a certain object with the right eye, then a second object lyingto the right of the first will cast its image on the median half ofthe retina. Impressions made upon the median half of the rightretina are referred to objects lying to the right of the fixation-point. For the same reason, retinal images on the temporal halfof the right eye are referred to objects to the left of the fixation-point. For the left eye the relations are of course exactly sym
Handbook of ophthalmology . explain almost all cases of pathological diplopia,upon the basis of the so-called empirical theory of vision. If wefix a certain object with the right eye, then a second object lyingto the right of the first will cast its image on the median half ofthe retina. Impressions made upon the median half of the rightretina are referred to objects lying to the right of the fixation-point. For the same reason, retinal images on the temporal halfof the right eye are referred to objects to the left of the fixation-point. For the left eye the relations are of course exactly sym-metrical. Applying this principle at the same time to both eyes, we have DIPLOPIA. 133 the laws for the occurrence of homonymous and of crossed doubleimages. In Fig. 34, suppose both eyes to be directed upon the point 6,then will the image a of the point a be cast in both eyes uponthe median half of the retina, and from what has been said it fol-lows that the image a, in the left eye, will be referred to an object Fig. to the left of the point 6, and the image a, in the right eye, toan object to the right of 6. The point a appears in doublehomonymous images. Relatively to the point a the visual axesconverge, since they intersect at 6. Convergence of the visualaxes causes homonymous double images, and conversely we can, asa rule, diagnose convergence of the visual axes from homonymousdouble images. On the contrary, impressions made on the tem-poral half of the retina are projected by the right eye to the left,and by the left eye to the right of the fixation-point. If a is thepoint fixed, then 6 casts its image h in both eyes upon the tempo-ral half of the retina; the point 6 appears double, and the imagein the right eye will be seen to the left, and the image in the lefteye to the right, of the point a. There is crossed diplopia. Rela-tively to the point h the visual axes are divergent; consequentlydivergence of the visual axes causes crossed double images, and con-versely
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