Assessment of longitudinal changes in rod function in intermediate age-related macular degeneration using a dark- adapted chromatic perimeter

Dr Chinh Nguyen1, Dr Rogan Fraser2, Dr Rose Tan2, Ms Emily Caruso2, Prof Robyn Guymer2, A/Prof Chi Luu2

1Royal Hobart Hospital , Hobart, Australia, 2Centre for Eye Research Australia, Melbourne, Australia

Purpose: It is well recognised that rod-mediated dark adaptation is significantly impaired in the early stages of AMD. Consistent with the geographical changes in retinal morphology seen in AMD, our baseline study was the first to demonstrate retinotopic variations in dark adaptation recovery rate and sensitivity in intermediate AMD. Longitudinal changes in dark adaptation in early stages of AMD remained unexplored. Therefore, the purpose of this study is to assess the longitudinal changes in rod-mediated dark adaptation in intermediate AMD, at multiple retinal locations, using dark-adapted chromatic perimeter.

Participants: Twenty participants with intermediate AMD and six age-matched control subjects from our baseline study were recalled for the one-year follow up study.

Methods: participants underwent complete ophthalmoscopic examination, multimodal imaging, and dark adaptation. Eyes were graded for AMD features (drusen, pigmentary changes, late AMD), in reference to the Beckman’s classification (defined as drusen ≥ 125 μm with or without pigmentary changes). One eye was designated as the study eye for DA testing.

Main outcome measures: The primary outcomes of this study were retinal sensitivity at 20 minutes and rod criterion time (RCT), which is defined as the time required for sensitivity to recover to a threshold of – 3.0 log unit stimulus intensity. Seven retinal locations were assessed for each patient.

Results: a total of 20 study eyes from 20 participants with intermediate AMD (mean age 72.0 ± 7.0 years) and 6 age-matched control eyes were analysed. There was no significant difference in visual acuity and clinically evident retinal structural changes in our study subjects at baseline and follow-up, aside from one participant who progressed to late AMD. Compared to baseline, progression of DA impairment was not seen in the control group at the one-year follow up. In contrast, both retinal sensitivity at 20 minutes and RCT were further compromised in AMD subjects, particularly in eyes with RPD. Retinotopic variation was once again demonstrated, with the most DA impairment seen within 6 degree eccentricity.

Conclusion: it is feasible to use DAC perimeter to detect longitudinal changes in rod mediated DA in patients with intermediate AMD, at one year follow up and at multiple retinal locations. We demonstrated an overall progression of DA impairment in both static and dynamic rod function at one year follow up in patients with intermediate AMD and more so in eyes with RPD, particularly within the central 6 degree retina.

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