By Mark Mattison-Shupnick, ABOM
After about age 10, the crystalline lens gradually yellows as you age, a successful result of absorbing UV to protect the retina from UV radiation’s accumulated effects. This increasing yellowness reduces illumination. This effect is also combined with a reduced sensitivity of the photoreceptors in the older adult’s eye. As a result, your eye’s ability to perceive color can also change dramatically.
At age 60, the amount of light reaching the photoreceptor cells of the retina is only one-third of the amount seen at age 20. This can affect a person’s ability to do everyday tasks. It might become more difficult to see the difference between blue, green and red clearly.
The brain tries to adjust to the diminished sensitivity to light. But it also means that we require more light to see well. We also become more sensitive to glare because for many, light entering the eye is more scattered rather than being focused precisely on the retina. In the aged eye, opacities in the lens, a pre-cataractous lens and cloudy media can further scatter light rather than allowing the production of a sharp image.
Combining these factors, some individuals have a harder time seeing clearly in every light condition and/or distinguishing between certain color shades. Then, in presbyopia, the lens becomes less flexible, may have some opacities and the pupil constricts to increase the depth of focus of the eye by blocking the light scattered by the periphery of the cornea. What in the past may have been just the right amount of light is no longer enough. All of the previous results in less illumination for the photoreceptor cells. You might ask, “Do patients notice the dimming of their world?”
The brain and the way that it creates “vision” are quite amazing. In dim light and/or as the lens yellows, the brain will correct for the reduced illumination by rebalancing color. But without all the light it needs, some of the objects in the field will be too dark to distinguish details clearly. The brain corrects for dim light but the definition of the leaves in the background is lost.
The Purkinje effect reduces the transmission of red in the human eye. The yellowing of the lens can dull the vibrancy of color and make distinguishing the differences of the shades of blues, greens and reds more difficult. Aging reduces the eye’s effectiveness, and lenses can further complicate the effects.