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Allannah J. Gaffney, Alison M. Binns, Tom H. Margrain; The Topography Of Cone-mediated Dark Adaptation Deficits In Age-related Maculopathy. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5739.
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Despite widespread agreement that dark adaptation is abnormal in age-related maculopathy (ARM), the optimal retinal location for detection of this deficit is unclear. The purpose of this study was to evaluate the effect of retinal location on the diagnostic potential of cone dark adaptation parameters. The time to the rod-cone-break (RCB) was also assessed as an indicator of rod adaptation kinetics.
Cone dark adaptation was monitored in 10 subjects with ARM and 10 age-matched controls, using four achromatic annuli (1, 4, 14 and 24º diameter) centred on the fovea. Following pupil dilation (tropicamide 1%), 80% of cone photopigment was bleached using a Maxwellian view optical system. Subsequently, threshold was monitored in the dark, using one of the stimuli, selected at random, until the RCB occurred, or for a maximum of 25 minutes. This procedure was repeated for each of the four stimuli. A 15 minute ‘wash out’ period was interleaved between successive trials. Threshold recovery data were modelled and the time constant of cone recovery (τ), final cone threshold and time to RCB determined. Diagnostic potential was evaluated by constructing receiver operating characteristic (ROC) curves for these parameters.
Cone τ was significantly longer for the ARM group at 2, 7 and 12º. The greatest difference between groups was observed at 12º from fixation. At this location, the mean τ was 3.49 (+/-2.02) and 0.64 (+/-0.38) minutes for ARM and control subjects respectively (p=0.002) and time to RCB was 17.68 (+/-5.37) minutes for ARM subjects and 9.05 (+/-2.11) minutes for control subjects (p=0.001). Correspondingly, ROC curves showed that the diagnostic potential of dark adaptometry is greatest for stimuli presented 12º from fixation; for cone τ the area under the curve (AUC)=0.99+/-0.02 and for time to RCB AUC=0.96+/-0.04.
This study has shown cone-mediated dark adaptation to be significantly impaired in ARM. The diagnostic potential of dark adaptation may be enhanced by measuring thresholds at an eccentricity of 12º. The observation that cone τ is highly diagnostic at this eccentricity is clinically significant, because this parameter may be quantified in as little as 10 minutes.
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