Ethnic variation in deep lateral orbital anatomy and its implications on decompression surgery

Aim: To describe differences in the deep lateral orbital wall (specifically, trigone) between Chinese, Malay, Indian and Caucasian subjectsMethods: Single-centre retrospective Computed Tomogram (CT)-based study; 20 subjects of each ethnicity were used from existing databases, matched for gender, average age and laterality. Subjects below 16 years of age were excluded. DICOM image viewing software CARESTREAM Vue PACS (Carestream Health Inc., USA) and OsiriX version 7.5 (Pixmeo., Switzerland) were used to measure deep lateral wall length, thickness and volume, as well as orbital depth and statistical analyses performed using Statistical Package for Social Sciences version 21 (IBM, USA).Results: In each group, there were 12 males (60%) and average age was not significantly different (p = 0.682–0.987). Using Chinese subjects as a reference, in Chinese, Malay, Indian and Caucasian subjects, mean trigone thickness was 13.68, 14.02, 11.60 (p < 0.001) and 13.80 mm, curved total wall length 45.23, 42.29 (p = 0.048), 41.91 (p = 0.020) and 45.00 mm, curved trigone length 23.03, 22.61, 17.19 (p = 0.011) and 18.76 mm (p = 0.030) and trigone volume 3120.97, 3221.01, 1613.66 (p < 0.001), 2498.46 mm3 (p = 0.059) respectively. Similarly, perpendicular orbital depth was 27.54, 24.97, 22.12 (p = 0.001) and 25.93 mm and diagonal orbital depth was 34.19, 33.27, 29.48 (p = 0.01) and 34.63 mm respectively.Conclusions: Indian and, to a lesser extent, Caucasian subjects have smaller trigones compared to their Chinese and Malay counterparts. Indian subjects also have shallower orbits and due care should be taken during decompression surgery.