As every physician should have a knowledge of what is known as professional cramp, a painful spasm of the finger, hand, forearm or arm from excessive use, as is often found in writers, telegraphers, pianists, violinists, typewriters, etc., so should every oculist have a knowledge that certain eye muscles, especially the ciliary, are liable to the same condition when subject to enforced contraction for prolonged periods of time.
No oculist who does much fitting for glasses has failed to notice that, although the greatest care has been observed in this part of his service, occasionally he will meet a case where it is impossible to obtain satisfactory results and relieve the annoying nervous symptoms that usually accompany refractive error, although under the effects of a cycloplegic the very best possible vision has been obtained. such patients are usually between the ages of 25 and 40 years, although cases much younger are occasionally encountered.
WRIGHT JW. CRAMP OF THE CILIARY MUSCLE DUE TO EYESTRAIN.. JAMA. 1903;XLI(11):648-650. doi:10.1001/jama.1903.92490300004001a