Abstract
Abstract: :
Purpose: To design a portable letter contrast sensitivity test with improved accuracy and ease of use, while maintaining correspondence with norms applicable to the Pelli–Robson Letter Contrast Sensitivity Chart. Methods: Using a Weibull function model of performance and Monte Carlo methods, I examined the psychometric properties of a letter contrast sensitivity test that uses the same Sloan letters as the Pelli–Robson, but which uses smaller log contrast steps that decrease from letter to letter, rather than 0.15 log unit steps between triplets of equal contrast. I examined several different test termination and scoring rules, as well as contrast steps. Additionally, I assessed the misreporting (lapse) rate empirically, using large high contrast letters, and untrained observers. Results: Misreporting rate was found to be negligible, and easily below 0.001. Given this, a test termination rule of two consecutive incorrect responses, with a correction for isolated incorrect responses prior to termination, was found to have better accuracy (29 % lower s.d.) than, yet excellent concordance with the Pelli–Robson. A small near–testing format has additional practical benefits for clinical testing. Conclusions: The newly available Lighthouse Letter Contrast Sensitivity Test, which affords many practical advantages, as well as increased accuracy, can still be interpreted using existing norms obtained from studies using the Pelli–Robson test.
Keywords: contrast sensitivity • age–related macular degeneration • aging: visual performance