The effect of orbital decompression surgery on interpupillary distance and angle kappa in patients with thyroid-associated orbitopathy.

PURPOSE: The purpose was to investigate the effects of orbital decompression surgery on postoperative changes in interpupillary distance (IPD) and angle kappa in patients with thyroid-associated orbitopathy (TAO).

METHODS: In patients with TAO who underwent orbital decompression surgery between January 1, 2014 and February 21, 2016, we measured exopthalmometry, IPD, inner intercanthal distance (IICD) and outer intercanthal distance (OICD) using a computer software program and angle kappa with an ORB scan II. We then analyzed preoperative and 3-month postoperative exophthalmometry, IPD, IICD, OICD and angle kappa to evaluate changes in eye position or rotation of the eyeball following orbital decompression surgery.

RESULTS: Fifty-four patients (35 women and 19 men) with a mean age of 34.59 (range, 16-64 years) were enrolled in this study. After decompression surgery, the IPD was significantly decreased by 1.76 mm (preoperative, 63.14 ± 3.93 mm; postoperative, 61.38 ± 3.84 mm; P < 0.001), but angle kappa, IICD, and OICD did not vary significantly (P = 0.814, P = 0.635 and P = 0.092, respectively).

CONCLUSIONS: A significant decrease in IPD was noted after orbital decompression in patients with TAO. However, there was no significant change in angle kappa. Therefore, the mechanism of change in the IPD is not an inward rotation of the eyeball, but rather an actual dorsal shift causing a wedging of the eye position itself within the orbit.