Essential Identity of Symptoms in Underaction and Overaction, However Caused.—Any of the ocular muscles may act insufficiently or to excess, and the overaction or underaction may be due to anomalies of structure, insertion or innervation. The terms paralysis and spasm are sometimes restricted to the innervational anomalies. But, as clinical evidence shows, the symptoms of either overaction or underaction are for the most part the same, no matter what the cause. It is hence convenient to group all of these anomalies in one category, without attempting to distinguish them into structural, insertional and innervational, and to use the terms paralysis and spasm to denote them, no matter what their origin.
This treatment of the subject is especially justified in cases of underaction. An inefficiency of the external rectus due to sheer muscular weakness or to a complete tenotomy resembles in practically all particulars one due to