Extraocular muscle fiber morphometry following combined recession-resection procedures in rabbits.

Abstract

In earlier studies, we have reported extraocular muscle fiber atrophy following recession and fiber hypertrophy following resection of a horizontal rectus muscle. Changes seen in the operated muscle were mirrored in the antagonist and were thought to be a compensatory response to sustained changes in tension across the muscle pair caused by the surgery and by changes in the rotational position of the globe. The purpose of this study is to examine the effects of combined recession-resection on extraocular muscle fiber diameter. In 16 anesthetized rabbits, a 6-mm recession of the medial rectus was combined with a 6-mm resection of the lateral rectus in the left orbit. The horizontal rectus muscles were removed from both orbits of four rabbits at 2-, 4-, 8-, and 16-week postoperative intervals. Cross-sections were cut from the midbelly of each muscle, and muscle fiber diameters were measured with a computerized morphometry unit. Mean fiber diameters from the operated orbit of animals at each postoperative interval were pooled and compared with means from the unoperated orbit using the paired-samples t test. No statistically significant change in fiber diameter was seen in either the global or orbital fiber layers at any postoperative interval examined. Because resection would be expected to increase and recession to decrease the resting tension across an agonist-antagonist pair, our results suggest that a combined recession-resection yields no significant net change in resting tension, and minimizes compensatory changes in extraocular muscle fiber diameter.