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Ioannis Dimopoulos, Antonia Johnson, Stacey Fisher, Matthew Tennant, Yves Sauve; Pan-retinal Functional Changes Associated With The Progression Age-related Macular Degeneration (amd). Invest. Ophthalmol. Vis. Sci. 2012;53(14):4377.
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We have previously described the following age-related changes in whole retina function as assessed with the full field electroretinogram in healthy human subjects (ffERG; Freund et al., Doc Ophthalmol 2011; 122:177-190): 1) less pronounced photopic hill, reflecting changes in the OFF-bipolar system; 2) prolonged a-wave implicit times, suggesting the occurrence of biochemical changes in rods and cones; and 3) selective a-wave amplitude reduction, indicative of maintained post-synaptic activity from rod ON-bipolar cells. In this study we investigated how AMD progression might impact on age-related changes in whole retina function.
We assessed whole retina function in human subjects using the full field electroretinogram (ERG). The groups studied consisted of: over 60 years (n=18 at 68±5y) with normal vision; over 60 years with dry AMD (early, based on three severity levels) in one eye and wet AMD (late) in the other eye (n=16 at 66±10y).
Recordings from early and advanced AMD eyes, when compared to the recordings obtained from eyes of age-matched subjects, revealed: 1) loss of the compensatory b-wave amplitude preservation under dark adapted conditions; 2) delays in dark adapted a-wave implicit times; 3) delays of elevation of bright flash b-wave amplitude as a function of time of dark-adaptation (2 min intervals over a 20-min after transition from light to dark); 4) loss of the photopic hill; 5) reduction in maximal photopic b-wave amplitudes recorded under a wide range of stimulus intensities; and 6) right shift in the b-wave photopic intensity response graph, reflecting loss of cone sensitivity in AMD. This latter was already pronounced at the earliest stage of early AMD (dry form). In fact, all changes reported above were observed at all AMD stages.
Our findings represent the first electrophysiological evidence supporting previous psychophysical findings of dark-adaptation defects in early AMD. Our results also indicate the loss of dark-adapted post-synaptic compensation in AMD. In addition to rod-driven changes, the present data point to a loss of cone sensitivity, which precedes the occurrence of any central vision distortion or acuity loss (earliest AMD stage). As such, these simples ERG tests might allow detection of AMD before any standard clinical manifestations (such as vision losses or ophthalmoscopically evident drusens) and therefore allow optimal precocious preventative intervention.
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