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Ian Murray, David Carden, Jeremiah Michael Kelly; New rapid digital dark adaptometer that shows high sensitivity and specificity for early AMD. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3705.
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© ARVO (1962-2015); The Authors (2016-present)
Rod mediated dark adaptation recovery is a highly sensitive functional index of the severity of AMD1. Here we describe a new technique for rapid, accurate assessment of the dynamics of rod recovery following a customised photo-bleach.
Thresholds are measured to a green (530nm) LED-based arc-shaped target (3° wide) presented at 8° eccentricity superimposed on a deep red (655nm) low luminance (0.05cd/m2) background. The bleach is localised to the target to avoid reducing foveal sensitivity. The intensity of the bleach can be set according to age, pupil size and media optical density of the observer. Typical bleach intensity values range from 1 to 5.4M scotopic trolands.sec which provides a bleach of 12% to 46% for pupils > 4mm diameter. In this study the bleach was always > 30%. A 5-parameter model and purpose developed software written in R are used to characterise the dark adaptation curves. The parameters and SDs are obtained in real time, which enables the test to be terminated when a reliable value for the slope of S22, the rod-mediated part of the curve, is reached. The technique was evaluated by testing 20 early AMD patients (age 69.5(6.8), 7 males; AREDS range 2-4), and comparing the slope of S2 with that for 20 age-matched normal observers (age 64.8(5.9), 9 males).
All observers were able to complete the test and reported it easy to perform. S2 was obtained in all normal observers. In 7 patients S2 was absent. The median slope of the S2 phase for the controls was -0.17(IQR: -0.19 to -0.16) lu/min and for the patients was -0.03(IQR: -0.12 to 0) lu/min. A logistic regression model was significant (intercept p<0.01 and slope p<0.002). For every 0.1 lu/min improvement in S2 the Odds Ratio of belonging to the normal group is 9.3(2.3 – 53). When compared with the AREDs grading, 19 of the AMD patients and 18 of the normals were correctly identified, yielding 95% sensitivity and 90% specificity. 95% of cases were analysable after 15.5 minutes.
The ease of use and rapid nature of the technique makes it ideal for ophthalmic clinics. It offers functional insight into the various stages of progression in dry AMD as revealed by retinal imaging. The high sensitivity/specificity suggests it will provide a functional end-point in the evaluation of new therapies.References1.Owsley et al (2007) Ophthalmology 114:1728-17352.Lamb and Pugh (2004). Prog Retin Eye Res 23:307-380
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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