Is poor dark adaptation a risk factor for age-related macular degeneration?
This week we reviewed the ALSTAR study (the Alabama Study on Early Age-Related Macular Degeneration). This collaborative effort sought to examine whether slowed rod-mediated dark adaptation in adults with normal macular health is associated with the incidence of age-related macular degeneration. The group concluded that adults greater than the age of 60 with normal macular health and abnormal rod-mediated dark adaptation were two times more likely to develop age-related macular degeneration three years later. Additionally, slowed dark adaptation is a functional marker for increased age-related macular degeneration risk.
Why did they study dark adaptation? Patients with early macular degeneration often notice problems with vision with decreased light, poor weather conditions, and nighttime. These symptoms occur despite having great visual acuity. These changes in vision are thought to be affected by the deposition of lipids in the macula. These depositions create a barrier that impedes the transfer of necessary nutrients such as vitamin A for rapid uptake and light adaptation. These changes affect the photoreceptors responsible for dark adaptation and motion detection as our the photoreceptors responsible for central vision have alternate sources for nutrients.
How did they study this? Participants were recruited from two primary eye care practices at the Callahan Eye Hospital at University of Alabama in Birmingham. They must be at least 60 years of age, have normal macular health in both eyes, and have no prior ocular disease, diabetes, Alzheimer's disease, Parkinson's disease, brain injury, or other neurological or psychiatric conditions. A total of 325 participants met the requirements and were able to follow-up three years afterward to complete the study. Each participant had an eye exam, fundus photos taken, and dark adaptation assessed psychophysically using the AdaptDx by MacuLogix (a sponsor of this study). The same procedures were completed after three years to determine the incidence of early age-related macular degeneration.
The average age of the participants was 67.8 years. More than 96% of the participants were white of non-Hispanic origin. Those with abnormal dark adaptation were average four years older and slightly more likely to be women. Dark adaptation increased by 1 minute on average at the three-year follow-up for those with normal dark adaptation at baseline and by 0.84 minutes on average in those with abnormal dark adaptation at baseline. 10% or 26/263 in the normal dark adaptation group, were found to have early macular degeneration at 3 years versus 20% or 13/62 in the abnormal dark adaptation group.
Why do we care about earlier detection? Earlier detection translates to earlier supplementation to help the macula. Diet and lifestyle changes lower the risk of worsening macular degeneration. Dark leafy vegetables, rich antioxidant diets, and avoiding tobacco smoke are recommended for all individuals with early macular degeneration. Earlier detection may lead to enrollment in clinical trials targeting prevention as well.