Introduction: The Spiral of Tillaux describes the historically accepted insertion distances of the medial rectus, inferior rectus, lateral rectus, and superior rectus from the limbus: 5.5 mm, 6.5 mm, 6.9 mm, and 7.7 mm, respectively. The corneal diameters are historically accepted to be 11.7 mm horizontally and 10.6 mm vertically in adults. We investigated the variability of the insertion distances of the extraocular rectus muscles from the limbus as well as the corneal diameters using eyes from human cadavers and compared our measurements to these historically accepted measurements.
Methods: A sample of 60 eyes were included. For each eye, a 360 peritomy was conducted and the conjunctiva bluntly dissected to view the sclera. Muscle hooks were utilized to isolate the extraocular rectus muscles. Calipers were used to measure the insertion distances of the rectus muscles as well as the corneal diameters.
Results: The mean rectus muscle insertions distances from the limbus were medial 5.28 mm, inferior 5.72 mm, lateral 6.40 mm, and superior 6.78 mm. These insertion distances were shorter than the historical benchmarks (p < .01). However, observed maximum distances of the rectus muscles were all greater than the historically accepted benchmarks, with the medial, inferior, lateral, and superior rectus muscles being 6.4 mm, 7.3 mm, 7.4 mm, and 7.8 m from the limbus, respectively. The mean width and height of the cornea were 11.7 mm and 10.7 mm, respectively, and similar to the expected ranges.
Conclusion: This study concludes that variability does exist from the historically accepted Spiral of Tillaux measurements. In addition, significant variation exists between male and female rectus muscle insertions. However, we did confirm that the rectus muscles followed the same spiral pattern described by the Spiral of Tillaux and concluded that the corneal diameters are consistent with previously accepted values.
Keywords: Anatomy; Spiral of Tillaux; cadaver; cornea; diameter; extraocular rectus muscles.