Investigation of the relationship between macular pigment levels and rod-mediated dark adaptation in intermediate AMD. Dark adaptation and macular pigment in AMD

Background: It has been shown that rod-mediated dark adaptation is significantly delayed in ageing, a change which is exacerbated in age-related macular degeneration. Levels of lutein and zeaxanthin, the two main constituents of macular pigment have been found in rod outer segments, indicating that the macular pigment may have an influence on rod-mediated dark adaptation. The aim of this study was to determine if rod-mediated dark adaptation is associated with central macular pigment levels in individuals with intermediate stage age-related macular degeneration.Methods: A cross sectional observational study included individuals with acuity better than 6/15 Snellen and intermediate stage age-related macular degeneration based on graded fundus photographs using an internationally accepted grading scale. Rod-mediated dark adaptation was assessed at five degrees eccentricity in the superior retina (inferior visual field) using the rod intercept time measure from the MacuLogix AdaptDx. Macular pigment optical density was measured at 0.5 degrees eccentricity using a heterochromatic flicker photometry-based method.Results: Twenty-seven individuals (mean age 76.7 years) with intermediate stage age-related macular degeneration and twenty-three age-matched normal controls (mean age 74.0 years) were recruited. Rod-mediated dark adaptation was significantly delayed in intermediate stage age-related macular degeneration compared with healthy controls (32.9 mins versus 10.7 mins, p<0.01). There was no statistically significant correlation between the rod intercept time and the level of macular pigment in those with intermediate age-related macular degeneration (r= -.04, p=0.85). Conclusion: The results did not support the hypothesis that higher macular pigment is associated with improved rod-mediated performance or that higher levels of macular pigment protect rod-mediated function in intermediate age-related macular degeneration.