The primary object of this paper is to account for the relative position of the eyes, binocular vision, and visual acuity in cases of permanent convergent squint operated upon early and thereafter followed up for a prolonged period. These cases did not undergo orthoptic training. By orthoptic training is understood, in the present paper, exercises to counteract the suppression of the image from the one eye, abolishing anomalous retinal correspondence and any incorrect relation between accommodation and convergence, and the use of prismatic lenses for improvement of the amplitude of fusion or compensation of the angle of squint. This investigation may, further, be regarded as a contribution to a more comprehensive task, viz., the elucidation of the mechanism of the development of esotropia. In this respect it is complementary to previous publications by me (Nordlöw* and Dahlberg and Nordlöw2). This aspect will be considered further in "Comment." REVIEW OF