Associations between abnormal rod-mediated dark adaptation and health and functioning in older adults with normal macular health

Abstract

Purpose: Delayed rod-mediated dark adaptation (DA) is characteristic of early age-related macular degeneration (AMD) and also can be observed in some older adults in normal macular health. We examine cross-sectional associations between rod-mediated DA and risk factors for AMD in older adults in normal macular health.

Methods: The sample consisted of adults aged ≥60 years old in normal macular health per grading of fundus photos using an established disease classification system. Rod-mediated DA was measured psychophysically following a photobleach using a computer-automated dark adaptometer with targets centered at 5° on the inferior vertical meridian. The speed of DA was characterized by the rod-intercept value, with abnormal DA defined as rod-intercept ≥ 12.3 minutes. We assessed several health and functional characteristics that the literature has suggested increase AMD risk (e.g., smoking, alcohol use, inflammatory markers, apolipoproteins, low luminance visual acuity, chronic medical conditions, body mass, family history).

Results: Among 381 participants (mean age, 68.5 years; SD, 5.5), 78% had normal and 22% had abnormal DA, with the prevalence of abnormal DA increasing with age. After age-adjustment, abnormal DA was associated with increased odds of elevated C-reactive protein (CRP), heavy use of or abstention from alcohol, high blood pressure, and drop in visual acuity under mesopic conditions.

Conclusions: Despite having normal macular health according to accepted definitions of AMD presence, approximately one-quarter of older adults recruited from primary eye care clinics had abnormal DA, which was associated with known risk factors for AMD, including elevated CRP.

Keywords: age-related macular degeneration; aging; dark adaptation; rod function.

Figure 1

Top: Color fundus photograph (right eye) of a 75-year-old participant in normal macular health who has normal rod-mediated DA as defined by the rod-intercept. Bottom: Color fundus photograph (left eye) of 72-year-old participant also in normal macular health yet who has abnormal rod-mediated DA.

Figure 2

The distribution of CRP values by quartiles for those with normal rod-mediated DA and those with abnormal DA. Higher quartiles correspond to higher CRP values. Quartile values are as follows: first quartile, ≤1.13 μg/mL; second quartile, 1.14–2.35 μg/mL; third quartile, 2.36–4.92 μg/mL; fourth quartile, >4.92 μg/mL. Those with abnormal DA were less likely to have CRP values in the lowest quartile (see also Table 3).

Figure 3

Adjusted ORs and 95% CIs describing the association between various levels of alcohol use and abnormal DA. The reference consists of those who reported that they drink but did not drink in the previous week. Abstainers and those who drink more than 14 drinks per week were more likely to display abnormal DA (see also Table 5).