Ageing and Vision

Age-Related Effects

As people age, their vision is affected by changes both to their eyes and their brains. The average pupil size decreases with age, so that less light enters the eye, and this reduction in light is compounded by changes in the structure of the lens.

Through the normal ageing process, even in the absence of cataracts (clouding of the lens), the lens becomes less transparent, blocking additional light from entering the eye, and changing the color of the light that does get through. Changes to the lens and intraocular media also increase light scatter, reducing the contrast of the retinal image. These structural changes to the lens also make it more difficult to focus on close objects as we age; this change in accommodative ability—the ability to change the optical power of the eye to focus on objects at different distances—is known as presbyopia, and is a normal part of the ageing process. The inability to focus on close objects without wearing glasses typically occurs between about 40 and 50 years of age, and the “near point” (the closest point on which one can focus) continues to move further away throughout our lifetimes. As young adults, people typically can focus clearly on objects about 10 centimeters away; by the time they reach 60 years of age, the near point has moved away to about 1 meter. Fortunately, by wearing appropriate optical corrections (glasses), seniors can overcome many of the difficulties associated with presbyopia.

These optical changes adversely affect vision, but research has shown that the most profound age-related effects on vision stem from changes in neural, rather than optical, processing. Blurring of the optics would lead to an inability to see fine details, resulting in a decrease in visual acuity. But ageing also decreases our contrast sensitivity—defined as the inverse of the lowest contrast needed to see different sized targets—even for mid-sized objects, although the most pronounced effects are seen for objects with more fine details. For example, the general shape and features of a face would remain visible throughout our lives, but it becomes more difficult to discriminate individual eyelashes around the eye, or fine wrinkles on a face. Based on behavioral techniques that can tease optical and neural factors apart, and based on studies in which stimuli are projected directly onto the retina, bypassing the optics, the age-related reduction in contrast sensitivity is largely the result of changes in neural processing, rather than of changes in the optics of the eye. Regardless of what causes a change in our acuity and contrast sensitivity, the net result is that the world appears a bit more blurry and washed out in the elderly.

...