"A" and "V" phenomena

Abstract

(1) A new classification of the "A" and "V" phenomena has been devised which differs,from those of Urist (1951-1954), Villaseca (1961), and Tamler (1961), and attempts to rectify their omissions. (2) The results of surgery in 27 cases of "V" esotropia, five cases of "A" esotropia, fourteen cases of "V" exotropia, four cases of "A" exotropia, and five cases of impure "A" and "V" phenomena are given. (3) It is pointed out that the fault in the "A" and "V" phenomena lies in the horizontal rectus muscles. (4a) The best approach for correction is bilateral recession in "V" tropias and bilateral resection in "A" tropias. Symmetrical surgery on the horizontal muscles produces a symmetrical result. By the recession of the medial recti in pure "V" esotropia, the deviation is corrected more on looking down and less on looking up. (b) Recession of the medial recti in cases of "V" esotropia corrects the deviation by from 86 to 100 per cent. without producing an overcorrection on looking up. (c) Uneven results are obtained with horizontal muscle surgery. If in "V" esotropia ipsilateral lateral and medial recti are operated upon, the results are far inferior to those obtained when only the medial recti are recessed. (d) There is no obvious vertical muscle defect in cases of impure and pure "A" and "V" phenomena. On the other hand this series shows that the vertical incomitance in cases of "A" and "V" phenomena in the cardinal directions of gaze is secondary to the horizontal deviation as it tends to disappear after operation on the horizontal recti only. (e) The medial rectus muscles, generally speaking, are stronger than the lateral rectus muscles. (f) In this series, we have seen that the incidence of impure "A" and "V" pheno-mena is only 9 per cent. In most of these cases the "A" and "V" phenomena are not associated with vertical incomitance in any direction of gaze. This further supports the idea that these phenomena are due to dysfunction not of the vertical but of the horizontal muscles.