Fig. 1. Diplopia results from simultaneous perception of similar images of the object of regard, that is, a Christmas tree, projecting onto noncorresponding retinal areas. Esotropia causes homonymous diplopia; clear image on macula of right eye is illustrated by solid lines, blurred image on nasal retina of left eye is illustrated by broken lines. The illustrated diplopic images are displayed according to the patient's drawing of them. Inset. Heteronymous diplopia in exotropia. (From Symposium on Strabismus, Transactions of the New Orleans Academy of Ophthalmology. St Louis: CV Mosby, 1971.)