Botulinum A toxin injection for restrictive myopathy of thyroid-related orbitopathy: effects on intraocular pressure

Abstract

Purpose To study the effect of extraocular muscle injections of botulinum A toxin on intraocular pressure in patients with thyroid-related orbitopathy. Design Retrospective observational case series. Methods The medical records of eight consecutive patients with restrictive myopathy secondary to thyroid related orbitopathy (TRO) who underwent botulinum A toxin injection from December 1997 to December 1998 were reviewed and analyzed retrospectively. All patients were seen at the University of California, San Diego (UCSD) Thyroid Eye Center, a university-based tertiary referral center. The main outcome measure was intraocular pressure (IOP) readings taken before and after injection in both primary gaze and upgaze (involving one eye in seven of the patients and both eyes in one patient). Intraocular pressure readings were measured by an unmasked physician using a Goldmann applanation tonometer. Results A statistically significant decrease in IOP in upgaze was noted 2 to 6 weeks following botulinum A toxin injection and in both fields of gaze (primary and upgaze) after 2 to 4 months. The mean IOP before injection was 21.4 ± 3.0 mm Hg in primary gaze and 29.9 ± 9.7 mm Hg in upgaze. The mean IOP, following injection at 2 to 6 weeks, was 19.2 ± 4.2 mm Hg ( P < .095) in primary gaze and 25.1 ± 5.9 mm Hg ( P < .023) in upgaze. At 2 to 4 months following injection, the mean IOP was 19.3 ± 3.9 mm Hg ( P < .044) in primary gaze and 27.7 ± 8.5 mm Hg ( P < .024) in upgaze. Six patients indicated improved ocular deviation, which was associated with a lowering of IOP. Two patients indicated no change in IOP or strabismic deviation following botulinum A toxin injection. Conclusion Botulinum A toxin injections cause a secondary effect to lower IOP in patients with restrictive strabismus associated with thyroid-related orbitopathy.