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P.N. Dimitrov, A.J. Vingrys, R.H. Guymer; Enhanced Diagnosis of AMD by Comparing Central and Peripheral Dark Adaptation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2112.
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Rods are affected in Age–related Macular Degeneration (AMD) especially in the paramacular region. In this work we contrast the dark adaptation of paramacular regions with peripheral retina in patients having different forms of AMD.
Dark adaptation recovery was compared at two retinal locations: 4° and 10° in 12 AMD patients. Group A comprised 7 people with high risk drusen in both eyes whereas Group B had drusen in the test eye and late stage AMD in their fellow eye (n=5). Adaptation was measured after ∼30% pigment bleach produced by a photographic flash. Stimulus (2°, 500 ms achromatic spot) was generated on a calibrated CRT monitor. Neutral density filters (2.6ND) were used to expose late cone and rod recovery phases in AMD patients. A running estimate of threshold was returned by a YES/NO paradigm using a modified tracking procedure. Data were modeled using two exponential decays to describe the cone and rod components.
We found significant abnormalities in the dark adaptation between groups at the 4° test location. Group A had significantly elevated cone absolute thresholds (Cab) when compared with Group B (–1.21 ± 0.17 vs –1.49 ± 0.07, p=0.042). Group A also had a significantly delayed rod–cone break (RCB; 26.5 ± 1.98 vs 12.1 ± 1.63, p=0.005). There was no significant difference between these groups at the peripheral location (Cab, –1.53 ± 0.19 vs –1.57 ± 0.17, p=0.63; RCB, 9.02 ± 1.45 vs –13.6 ± 2.77, p=0.59). Comparing central to peripheral performance, Group A showed a significantly greater delay in RCB at central locations only (p=0.003).
These findings extend past observations for selective rod vulnerability by showing both rod and cone losses in central locations. We find that people with high risk drusen have marked central dark adaptation abnormalities not evident in people who have late stage AMD.
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