Purchase this article with an account.
T.J. Van Den Berg, J.E. Coppens, L. Franssen; New Approach for Retinal Straylight Assessment: Compensation Comparison . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4315.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: Presently no instrument or method exists that is generally accepted for routine clinical assessment of (functional) retinal straylight. Yet retinal straylight is the cause of important patient complaints such as glare hindrance and contrast loss. It results from disturbances in the optical media, increasing light scattering over angles of 1 to 90 degrees. Its assessment would help to decide on surgery of (early) cataract, or to evaluate corneal or vitreal turbidity. The psychophysical technique of the "direct compensation method" was adapted to make it suitable for routine clinical assessment of retinal straylight. Methods: When looking at a flickering annular field, subjects perceive a (faint) flicker in the center because of retinal straylight. When counterphase flickering light is presented in that center, the straylight flicker can be cancelled (compensated) giving a quantitative measure ("direct compensation" method). In the new approach the central test field is subdivided in two half fields, one with and one without counterphase compensation light. The subject’s task is a forced choice comparison between the two half fields, to decide which half flickers more strongly. Compensation level is varied to encompass the straylight value itself as well as twice the straylight value (overcompensation). Note that with compensation at twice the straylight value, retinal flicker equals flicker with no compensation. In other words, the two test field halves seem to flicker equally strongly (after appropriate adjustment of mean luminance). For still larger compensation levels, the compensated half of the comparison fields is seen to flicker more strongly. A maximum likelihood estimation is performed, fitting a psychometric function to the patient responses for 25 such comparisons, including a reliability estimate of the obtained straylight value. A theoretical form for the psychometric function was derived and experimentally verified. The method was applied in 2400 subjects in the European GLARE study. Results: Repeated measures standard deviation for the method is about 0.06 log units, to be compared with differences in the young normal population of 0.2 log units, increasing with healthy aging by 0.5 log units at 80 years, and by 1.0 or more log units with (early) cataract or corneal disturbances. Conclusions: The compensation comparison method for measuring retinal straylight is suited for clinical use to diagnose patients with complaints caused by large angle light scattering in the eye such as early cataract. A commercial instrument (the C–Quant by Oculus) employs this new method.
This PDF is available to Subscribers Only