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Allannah J. Gaffney, Alison M. Binns, Tom H. Margrain; A Comparison Of Psychophysical & Electrophysiological Methods For Assessment Of Cone Dark Adaptation In ARM. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4380. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Dark adaptation is an important clinical tool for the diagnosis of age-related maculopathy (ARM). Cone dark adaptation is particularly attractive because it can identify people with ARM in a relatively short recording period. We compared the diagnostic potential of established electrophysiological & psychophysical techniques for measuring cone dark adaptation in ARM.
Cone dark adaptation was measured in 10 subjects with ARM & 10 age-matched controls on two days. Prior to dark adaptation, subjects’ pupils were dilated (1.0% tropicamide) & an 84% cone photopigment bleach (5.20 log phot.td for 120secs) administered to the test eye. At the first visit, threshold was monitored continuously for 30mins using an automated psychophysical method of limits. The stimulus was a 12º diameter achromatic annulus, centred on the fovea. At the second visit, cone dark adaptation was assessed using the focal cone electroretinogram (ERG) photostress test. Focal cone ERGs were recorded using a central 20º diameter, amber (max = 595nm, half-height bandwidth = 17nm), square wave 41Hz stimulus, with a time-averaged illuminance of 1500 phot.td). Eight pre-bleach ERGs were recorded as a baseline. Post-bleach ERGs were recorded every 20secs for 5mins. Recovery data (psychophysical thresholds & first harmonic of ERG responses) were plotted as a function of time after the bleach & modelled using an exponential function. Receiver operating characteristic (ROC) curves were used to compare the diagnostic potential of the time constant of cone recovery (τ).
Cone τ was significantly longer in the ARM group for psychophysical (p<0.05) & electrophysiological (p<0.02) methods. Both techniques were highly diagnostic for ARM: area under the curve (AUC) = 0.80 +/- 0.11 for the psychophysical test & 0.72 +/- 0.14 for the focal cone ERG photostress test. There was no statistically significant difference in the AUC of the two techniques.
Consistent with previous reports, cone dark adaptation was significantly impaired in ARM. Although electrophysiological methods are more objective than psychophysical methods of dark adaptation measurement, the diagnostic potential of cone dark adaptation in ARM was similar for both methods. There is now an urgent need for longitudinal studies to clarify the value of dark adaptation as a biomarker for ARM.
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