Impaired Dark Adaptation: The Earliest Biomarker of AMD
Before drusen are visible, an invisible layer of cholesterol builds up between the pigmented layer of the retina (RPE) and the elastic layer of Bruch’s membrane. These cholesterol deposits—basal laminar (BLamD) and basal linear (BLinD)—cause oxidative stress and inflammation, hindering nutrient transportation to photoreceptor cells.
As photoreceptor cells die, it becomes harder for the eyes to adjust to darkness and night vision declines. This dark adaptation impairment is the first sign of age-related macular degeneration (AMD). The cholesterol deposits grow over time. Where they become sufficiently thickened, the lesion becomes clinically detectable as a druse. The first visible druse caused by AMD is just the tip of the iceberg of these lesions.
Research has shown that impaired dark adaptation function can be detected at least three years before drusen are clinically evident, allowing for earlier diagnosis, treatment and monitoring of AMD.