To the Editor.
—I read with great interest the article by Sher et al1 in the November 1991 issue of the Archives and noted that limited information was provided about the methods used. No details were given on the method of test administration during which it is important to control the patient's criterion for judging visibility.2 For example, two patients may have the same contrast sensitivity, but one may require a higher objective contrast before being willing to hazard a response on a test. The most reproducible results are obtained using the forced-choice method of testing,3 in which the patient is required to give a response even if the letters or test pattern appears illegible until a predetermined number of incorrect responses are given. No details were provided about the test (Multivision Contrast Tester 8000, Visitech Consultants Inc, Dayton, Ohio), which consists of the Visitech contrast sensititivy