Duane first described V-pattern strabismus in 1897.
Other investigators also studied these phenomena, contributing to the understanding of them. Costenbader and colleagues recommended measuring the horizontal deviations in upgaze and downgaze as part of all routine motility examinations.
Two types of V-patterns can occur, as shown in the images below.
V-pattern exotropia is an exodeviation with greater exotropia in upgaze than in downgaze.
V-pattern esotropia is an esodeviation with greater esotropia in downgaze than in upgaze.
Comitant horizontal deviations are those in which the angle of deviation is the same in all gaze positions. Incomitant horizontal deviations are those in which the angle of deviation varies in different gaze positions. Horizontal deviations may have lateral incomitances and vertical incomitances. In lateral incomitances, significant differences exist in the amount of horizontal deviation in primary gaze versus side gaze, whereas, in vertical incomitances, significant differences exist in the amount of horizontal deviation in upgaze versus downgaze.
When the eyes diverge more than 10 prism diopters (PD) from upgaze to downgaze, an A-pattern is present; when the eyes converge more than 15 PD from upgaze to downgaze, a V-pattern is present.
Other types of vertical incomitances, which are less common, include X, Y, and lambda patterns. This discussion is limited to V-pattern strabismus.