Structural changes associated with delayed dark adaptation in age-related macular degeneration

Abstract

Purpose : Visual acuity is a limited functional endpoint for age-related macular degeneration (AMD), as it remains largely unchanged until late stage AMD. Impairment in night vision is a common symptom of AMD patients, and a consistent prolonged time of rod-mediated dark adaptation (DA) has been described even in the early stages of the disease. This study aimed to identify the most relevant structural parameters associated with time to dark-adapt in AMD.

Methods : Cross-sectional, prospective study, including patients with AMD. All participants underwent ophthalmologic exam; color fundus photographs (CFP); spectral-domain OCT with enhanced-depth imaging protocol; and AdaptDx® DA testing - extended protocol (20 minutes) – in both eyes. Tests with ≥30% fixation error were excluded. AMD staging was based on CFP AREDS system. A software program was developed to map the DA 2^o testing spot (at 5^o on the superior retina) on the OCT b-scans and to obtain the mean retinal and choroidal thickness in the same area. Two independent graders evaluated the b-scans’ regions included in this spot and recorded the presence of several AMD-associated abnormalities. Univariate and multivariate multilevel mixed effect linear models (accounting for correlated outcomes between 2 eyes) were used for analyses.

Results : We included 54 eyes (n=30 patients, mean age 70.2 ± 6.5 years) with a median rod intercept time (RIT) of 19.41 minutes, ranging from 4.13 to ≥20 minutes (n=26, 48.2%). Most eyes presented intermediate (n=35, 64.8%) or late AMD (n=14, 25.9%) and the disease stage was an independent predictor of RIT in the univariate and multivariate analyses (p≤ 0.038). Similarly, the presence of any structural abnormalities in the mapped OCT areas correspondent to the DA testing spot was significantly associated with a prolonged RIT in the univariate and multivariate assessments (p<0.001 for both). The best multivariate model revealed that, controlling for age, a reduced retinal thickness (β=-0.07, p=0.022) and the presence of classic drusen (β=3.77, p=0.007) in the mapped regions were significantly associated with a prolonged RIT.

Conclusions : Our work demonstrates a structural functional correlation in AMD. We found that reduced retinal thickness and classic drusen seen on OCT are associated with an increased time to dark-adapt.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.