Efficiency in reading with closed-circuit television for low vision.

A closed circuit television (CCTV) magnifier was used to measure the reading rates of nine fluent low-vision subjects. Performance was found to be dependent on field width, character size, and the number of characters displayed in line. A field width of 70 degrees and a mean of 24 characters were commensurate with the fastest reading rate. The optimal character size that elicited the fastest reading was determined for each subject. In seven of the nine subjects, this differed from the character size selected by chance at their initial CCTV sessions, prior to these experiments. A clinical procedure is recommended, which avoids inappropriate choice, and guides the examiner in achieving directly the most efficient CCTV reading conditions for each individual patient.