Prioritising downgaze alignment in the management of vertical strabismus for thyroid eye disease: principles and outcomes.

OBJECTIVE: To evaluate outcomes of surgery for vertical strabismus in thyroid eye disease (TED) employing a set of surgical principles aimed at avoiding reversal of downgaze deviation while restoring binocular single vision (BSV). METHODS: A retrospective review of consecutive patients undergoing vertical strabismus surgery for TED using a set of surgical principles between 2008 and 2017. Principle outcome measure was the presence of BSV in primary position and downgaze 3 months postoperatively and at latest follow-up. RESULTS: Thirty five patients (29% male) with a mean age of 58 years (range 31-83 years) were included. Median follow-up was 16 months. At presentation, 17 (49%) used monocular occlusion to avoid diplopia; the remainder used a prism and/or abnormal head posture. In 12 (34%), combined horizontal and vertical muscle surgery was required. Median (inter-quartile range) preoperative vertical deviations in primary position and downgaze respectively were 20 prism dioptres (Δ) (15, 30) and 18Δ (8, 22), which improved to 1Δ (0, 3) and 1Δ (0, 3) after the first operation. BSV in primary position and downgaze, without prism, after a single surgery was achieved in 29 (83%). Second surgery was required in 5 (14%) and one patient who had reactivation of her TED required a third surgery. At final follow-up (median 16 months), 32 (91%) were diplopia free without prisms; 3 (9%) used a small prism correction (range 2-12Δ); no patients were left with intractable diplopia. CONCLUSIONS: Our management principles are characterised by prioritising downgaze alignment to avoid downgaze diplopia reversal, whilst limiting adjustable sutures and employing standard surgical dosing. They give favourable outcomes in TED associated vertical strabismus.