Fig. 3.

This patient had a right hypotropia, which measured 30Δ in primary position and 15Δ in extreme downgaze, as well as a marked esotropia measuring 60Δ in primary position. It was difficult to achieve fusion preoperatively but she could achieve tenuous BSV in free space, in downgaze with prismatic correction. She had a prism fusion range of 5Δ in the direction of vertical misalignment (able to achieve tenuous BSV in downgaze with a 40Δ base out prism and from 15 to 20Δ base up right eye). She had asymmetrical, restricted ductions as shown. Perioperative FDTs on the right showed restrictions of the order −6 to elevation, −1 to depression, −5 to abduction and −2 to adduction. FDTs on the left showed −3 to depression, −2.5 to elevation, −3.5 to abduction and free to adduction. A target angle of vertical correction was taken as 20–25 dioptres, the right inferior rectus was recessed 8.5 mm, leaving it at 15 mm from the limbus. She also had a net total of 11.5 mm of horizontal surgery with bimedial rectus recessions. Postoperatively she had a small vertical phoria in primary position (two dioptres right hypophoria) with reversal of her hyoptropia only in extreme downgaze (four dioptres left hypotropia). She had BSV in primary position, up to 20° of upgaze and extending >40° in downgaze