A and V syndromes

A and V syndromes are ocular deviations in which horizontal deviations are vertically inconstant:

• A pattern: there is more esotropia, or less exotropia, in upgaze compared to downgaze
• V pattern: there is less esotropia, or more exotropia, in upgaze compared to downgaze

A or V patterns occur in 50% of patients with an esotropia or exotropia. The amount of deviation is assessed using the alternate cover test at 15 degrees up and 25 degrees down gaze. An A pattern is present when the difference is greater than 15 prism dioptres; a V pattern when greater than 10 prism dioptres.

V-esotropia is the most common, followed by A-esotropia, V-exotropia and A-exotropia. The cause varies. V patterns often have overaction of the inferior oblique muscles which are primarily, elevators; A patterns, overaction of the superior oblique muscles - primarily, depressors. Visual axes tend to converge in downwards gaze so that in V-esotropia, there may be overaction of the medial recti - adduction; and in V-exotropia, overaction of the lateral recti - abduction.

Treatment is by recession and resection of the horizontal muscles. To enhance the effects of these procedures, the medial recti muscles are displaced towards the apex of the A or V - i.e. upwards in A patterns, and downwards in V patterns. The lateral recti are displaced away from the apex. The inferior obliques may be recessed in V patterns.