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I commend Dr Mims for his thoughtful comments about IOOA. He believes that primary IOOA is caused by muscle hypertrophy and secondary IOOA could be explained by contracture. He bases this on his anecdotal observation at surgery that IOs that are primarily overacting typically appear larger than IOs that are overacting secondary to fourth-nerve palsy.¹ Dr Mims feels that contracture would not account for the hypertropia being larger in gaze up and in than in horizontal sidegaze.

A hypertrophied muscle is one that is enlarged owing to individual muscle fibers being larger than normal.² The term hypertrophy merely describes anatomy and does not denote an alteration of function a priori. It is not clear to me why an IO that is larger than normal should necessarily cause a hypertropia that is greatest gaze up and in, unless it also generates an increased contractile force. Reading between the lines . . . [Full Text of this Article]

AUTHOR INFORMATION
Burton J. Kushner, MD