Abstract
Abstract: :
Purpose: Many applications require knowledge of lens absorption. Measuring lens optical density (OD), however, is often difficult and time–consuming. For example, psychophysical measurement typically requires a long period of dark adaptation (e.g., about 40 minutes) and assessment of absolute scotopic thresholds. In this study, we examined an efficient scotopic method for measuring lens OD. Methods: 30 subjects (mean age = 24+/–7 years) were assessed. Relative scotopic thresholds were obtained after 15–minutes of dark adaptation using slow–rate (2 Hz) flicker photometry. The 3–degree test stimulus, presented at 10–degress nasal, alternated between measuring wavelengths (420 and 460 nm) and a reference field (540 nm). Results: Full spectral curves were obtained for three subjects. The abbreviated method provided spectral data that matched standard V’λ curves. Average values for the larger sample at 420 and 460 nm were consistent with published data using the standard scotopic method. Conclusions: Using a relative rather than an absolute method reduces the time needed for dark adaptation and is an easier task for subjects to perform. The close match of this data with standard scotopic curves and the consistency with past literature suggests that this method yields valid lens estimates. We are currently examining the validity of an even faster flicker–based photopic procedure.
Keywords: clinical research methodology • clinical laboratory testing • anterior segment