Impaired Dark Adaptation: Earliest Sign of AMD
The earliest warning sign of age-related macular degeneration (AMD) is trouble seeing at night. Many people blame night vision problems on the normal aging process. But it could be something more.
If you begin having difficulty seeing at night, it’s time to talk with your eye doctor. You may have impaired dark adaptation.
What Is Dark Adaptation?
Dark adaptation is the ability of your eyes to adjust from seeing in the light to seeing in the dark. Think of going from bright sunlight into a darkened movie theater. How long does it take your eyes to adjust? That is dark adaptation.
How Does Dark Adaptation Work?
The human retina can perform light-detection functions in an incredible array of light intensities, from bright sunlight to dimly lit rooms. Two types of photoreceptors — light-sensitive cells — have evolved to help eyes adjust to seeing in the dark:
- Cones: These photoreceptors function best in relatively bright light and can respond to extremely high levels of illumination. Yet, they’re not as reliable in dimly lit situations.
- Rods: These cells act as light detectors, even in lower light. They can respond to just one light photon, thus operating at the physical limit of light detection.
While both cones and rods are involved in dark adaptation, cones adapt faster. So, the first few minutes of dark adaptation reflect cone-mediated vision — during which you can hardly see your surroundings. Rods work slower, but once they take over, your eyes adapt to darkness.
The Relationship between Dark Adaptation and Age-Related Macular Degeneration
Research shows that dark adaptation weakens at the earliest stages of age-related macular degeneration. At the onset of AMD, the accumulation of drusen (yellow deposits under the retina made up of lipids and protein) deprives the rods and cones of nutrients, causing oxidative damage and inflammation. This eventually leads to degeneration of photoreceptor cells. Because the rods die sooner than cones, it becomes more difficult for your eyes to adjust to darkness. This is why you might experience trouble seeing at night, reading in dim light, or adjusting to seeing in the dark.
As the disease progresses, night vision difficulties increase. This diminished light adaptation could be a warning sign to visit your eye doctor and investigate dark adaptation testing. Measuring dark adaptation speed can be useful in the detection of AMD.
Breakthrough in Dark Adaptation Testing
Testing dark adaptation speed with a new tool, called AdaptDx Pro™, can help identify AMD with 90% sensitivity.
The first AMD symptom I noticed was problems reading in a dim room. When the light was bright, I had no issues. But when the light was dimmed, I just could not make out that small print.