Eyes
As people age, the following occurs:
Loss of near vision: During their 40s, most people notice that seeing objects closer than 60-100 cm becomes difficult. This change in vision, called presbyopia, 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 becomes less transparent. There are two types of photoreceptors in the human retina, rods, and cones. Rods are responsible for vision at low light levels (scotopic vision). They do not mediate color vision and have a low spatial acuity. Cones are active at higher light levels (photopic vision), are capable of color vision and are responsible for high spatial acuity. The central fovea is populated exclusively by cones. There are 3 types of cones which we refer to as the short-wavelength sensitive cones, the middle-wavelength-sensitive cones, and the long-wavelength sensitive cones or S-cone, M-cones, and L-cones for short. The light levels where both are operational are called mesopic. 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. 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 look less bright and contrasts between different colors may be more difficult to see. Blue looks grayer, and blueprint or background look washed out. However, older people 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 become more sensitive to glare. However, increased sensitivity to glare is often due to darkened areas in the lens or to cataracts.
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.
Older people see more tiny black specks moving across their field of vision. These specks, called floaters, are bits of normal fluid in the eye that have solidified. Floaters do not significantly interfere with vision. Unless they suddenly increase in number, they are not a cause for concern.
The eyes tend to become dry. This change occurs because of the number of cells that produce fluids to lubricate the eyes decreases. Tear production may decrease.
The appearance of the eyes changes in several ways: