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In 1947 Swan described a squint syndrome' which he subsequently named the blind spot syndrome/ In these two reports, Swan presented a unique form of comitant esotropia, accompanied only occasionally by diplopia, in spite of the fact that no sensory adaptation could be observed. The author reasoned that the physiological blind spot played the role of a suppression scotoma provided by nature to alleviate diplopia and making any other form of adaptation unnecessary. One of us (GKvN)' and others1'5 have had reservations concerning the validity of this entity. These reservations will be discussed and new evidence presented to the effect that the blind spot cannot possibly offer the only means of avoiding diplopia and confusion in the so-called blind spot syndrome.
The clinical characteristics of the blind spot syndrome, as described in the ophthalmic literature1,2,6-10 are summarized in Table 1. From this description, one would expect these patients to have a fairly constant angle of esodeviation between 12 and 18° at all fixation distances and positions of gaze for the blind spot to be effective in alleviating diplopia. Some authors have commented on the high incidence of this angle of strabismus in their patients, especially after incomplete surgical correction of an esotropia.2*"7 However, we have reviewed 100 consecutive cases of congenital esotropia operated upon at Texas Children's Hospital and found a deviation between 12 and 18° in only 4% of this group. With the description of the blind spot syndrome as listed on Table 1 in mind, a number of points must be discussed.
First, for the optic nerve head to assume the function of a scotoma in avoiding diplopia one would expect the size of the retinal image in the deviated eye to be smaller than, or the same size as the optic disc. If one accepts the normal size of the optic disc to be about 5° or 1.5 mm in diameter, one can determine by simple calculations the area covered by the scotoma at various distances of fixation" (Table 2). It is obvious from these data that under normal conditions of seeing numerous objects exceed these measurements and diplopia should be reported almost constantly. However, according to the literature, patients thought to have a blind spot syndrome do not often complain...