What is a category of by-product that is produced in the body and has been related to aging?

As people age, the following occur:

• The lens stiffens, making focusing on close objects harder.

• The lens becomes denser, making seeing in dim light harder.

• The pupil reacts more slowly to changes in light.

• The lens yellows, changing the way colors are perceived.

• The number of nerve cells decrease, impairing depth perception.

• The eyes produce less fluid, making them feel dry.

A change in vision is often the first undeniable sign of aging.

Changes in the lenses of the eye can cause or contribute to the following:

• Loss of near vision: During their 40s, most people notice that seeing objects closer than 2 feet becomes difficult. This change in vision, called presbyopia Causes

  
  , occurs because the lens in the eye stiffens. Normally, the lens changes its shape to help the eye focus. A stiffer lens makes focusing on close objects harder. Ultimately, almost everyone gets presbyopia and needs magnifying reading glasses. People who need glasses to see distant objects may need to wear bifocals or glasses with variable-focus lenses.

• Need for brighter light: As people continue to age, seeing in dim light becomes more difficult because the lens tends to become less transparent. A denser lens means that less light passes through to the retina at the back of the eye. Also, the retina, which contains the cells that sense light, becomes less sensitive. So for reading, brighter light is needed. On average, 60-year-olds need 3 times more light to read than 20-year-olds.

• Changes in color perception: Colors are perceived differently, partly because the lens tends to yellow with aging. Colors may look less bright and contrasts between different colors may be more difficult to see. Blues may look more gray, and blue print or background may look washed out. These changes are insignificant for most people. However, older people may have trouble reading black letters printed on a blue background or reading blue letters.

The pupil of the eye reacts more slowly to changes in light. The pupil widens and narrows to let more or less light in, depending on the brightness of the surroundings. A slow-reacting pupil means that older people may be unable to see when they first enter a dark room. Or they may be temporarily blinded when they enter a brightly lit area. Older people may also become more sensitive to glare Glare and Halos A number of other symptoms and problems can affect the eyes, including changes in the appearance of the eyes, color blindness, dry eyes, glare and halos, impaired depth perception, itchy eyes... read more . However, increased sensitivity to glare is often due to darkened areas in the lens or to cataracts Cataract A cataract is a clouding (opacity) of the lens of the eye that causes a progressive, painless loss of vision. Vision may be blurred, contrast may be lost, and halos may be visible around lights... read more

Fine details, including differences in shades and tones, become more difficult to discern. The reason is probably a decrease in the number of nerve cells that transmit visual signals from the eyes to the brain. This change affects the way depth is perceived, and judging distances becomes more difficult.

The appearance of the eyes changes in several ways: