Morphometric Variations of Extraocular Muscles in a Caucasian Cohort: A Pilot Study on the Surgical Implications of Ethnic Diversity

Precise anatomical knowledge of the extraocular muscles (EOMs) is crucial, particularly for managing "slipped" or "lost" muscles in strabismus surgery. This pilot study provides the first morphometric data for Caucasian-specific, cadaveric orbits, revealing significant deviations from accepted anatomical norms. 6 Caucasian, formalin-embalmed orbits (86-92 years) were dissected using a superior orbitotomy approach at the Human Anatomy Unit, University of Birmingham. Recti and oblique lengths, insertion widths, limbal distances, and inter-recti distances were measured using a triple-observer, string-arc technique to account for scleral curvature. Data on muscle length, width, and limbal distance were compared with Thai, Mexican, Indian, and Taiwanese datasets using Welch's t-tests; inter-recti spacing was assessed observationally. Significant deviations were observed across all assessed parameters, most notably in relation to the Spiral of Tillaux, with an ascending limbal distance order of lateral rectus (LR) < medial rectus (MR) < inferior rectus (IR) < superior rectus (SR). Relative to the compared East Asian cohorts, the Caucasian population exhibited significantly more posterior insertions in three of the four recti muscles (P < 0.05). Inter-recti distance comparison identified the IR-MR gap as consistently the narrowest surgical corridor. Morphometric data of the EOMs including the possible inter-ethnic differences suggested in this study, should be further established through additional research. Moreover, further studies are needed to validate the use of inter-recti distance as a useful surgical morphometric parameter that could guide more precise and tailored approaches in strabismus surgery.