Accommodation and Presbyopia
Presbyopia is the gradual loss of our eyes’ ability to focus on nearby objects.
Accommodation, the mechanism by which the eye changes focus from distant to near images, occurs when the action of the ciliary muscle on the zonular fibres changes the lens shape. The lens substance is most malleable during childhood and the young-adult years, progressively losing its ability to change shape with aging.
In adolescents, the accommodative power is generally almost 12.00–16.00 diopters(D). By the age of 40s, the power decreased to 4.00–8.00 D. After the age of 50s, the average accommodative power decreased to less than 2.00 D.
Presbyopia is the result of a gradual loss of accommodative response. After 40 years of age or older, this decreased accommodation becomes clinically significant and requires glasses or lenses for near targets like reading.
Inside our eyes, we have a natural lens. The lens bends light rays that come into the eye to help us see. The lens should be clear.
If we have cataract, our lens has become cloudy. It is like looking through a foggy or dusty car windshield. Things look blurry, hazy or less colorful with a cataract.
Aging is the most common cause. This is due to normal eye changes that begin to happen after age 40. That is when normal proteins in the lens start to break down. This is what causes the lens to get cloudy. In people over age 60 usually start to have some clouding of their lenses. However, vision problems may not happen until years later.
Age-related macular degeneration (AMD) is a progressive, degenerating disease of the neural layer of the retina which affects central vision after a certain age. Fine details of central vision in both near and far start to vanish, but peripheral (side) vision can still be normal. For instance, imagine looking at a clock with hands. With AMD, the clock’s numbers are clear, but not the hands.
It happens when the central portion of our retina, called the macula, wears down. The retina is the light-sensing nerve tissue at the back of the eye. It can cause severe visual loss and even blindness if left untreated.
AMD is one of the leading causes of vision loss in the aging population, and still without a cure in modern medicine.