Anterior segment optical coherence tomography of previously operated extraocular muscles

Background and Purpose: To assess the possibility of determining the insertion distance from the limbus of previously operated extraocular rectus muscles (EOM) with the Heidelberg Spectralis anterior segment optical coherence tomography (AS- OCT). Patient and Method: Subjects with a history of previous strabismus surgery underwent AS- OCT of the EOM before planned additional strabismus surgery. The EOM insertion distances from the limbus were measured pre- operatively on the AS- OCT and compared to the caliper distance measured during the strabismus surgery. Results: Ten previously operated muscles on nine subjects underwent AS- OCT before subsequent additional strabismus surgery. Four additional un- operated muscles subsequently operated on, were also imaged with the AS- OCT pre- operatively. Subject ages ranged from 13-52 years old (mean ± SD; 27.9 ± 13.2). The muscle insertion could be definitely identified in 6/ 10 muscles previously operated and 4/ 4 un- operated muscles. The difference between the two measurements of limbus to insertion in previously operated muscles was ≤1mm in 3/ 6, and ≤1.5mm in 6/ 6; < 1mm in 4/ 4 un- operated muscles. Of the four insertions not readily identifiable, two revealed the presence of the muscle with scar tissue; the other two, the muscle insertions, were not visible, which showed that the muscle was at least a minimal amount from the limbus. Conclusion: Our study showed that the Heidelberg AS- OCT is capable of imaging previously operated EOM, which can give valuable information to the strabismus surgeon. The information from the AS- OCT was useful in all cases. The insertion to limbus measurements between pre- operative and intra- operative were within 1.5mm in all of the cases that the muscle insertion was able to be identified. The ability to accurately image EOM insertions has significant implications for the pre- operative procedure planning in previously operated and complicated strabismus patients.