Abstract

Since the early 1970s, researchers have been measuring the resting state of accommodation (e.g., Leibowitz & Owens, 1975a, 1978; Epstein, Ingelstam, Jansson & Tengroth, 1981; Heron, Smith & Winn, 1981), operationally defined by Leibowitz & Owens (1975b) as the "dark focus" of accommodation. They proposed that the dark focus could explain anomalous refractive errors that occur in difficult visual conditions such as at night, looking at an empty field or working with an instrument. Based on this concept the dark focus could serve as a basis for predicting and correcting such “anomalous myopias” (Leibowitz & Owens, 1975b; Owens & Leibowitz, 1976). Later studies questioned the clinical utility of the dark focus, however, because different measurement techniques yield varying results. Laser optometers typically find more “myopic” dark focus values, while infrared optometers (e.g., Canon R1) obtain more distant dark focus values (e.g., Post, Johnson, & Tsuetaki, 1984; Post, Johnson, & Owens, 1985).

© 1998 Optical Society of America