ACCOMMODATION is the process in which the eye changes its focus from a far target to a
near one. There are three structures inside the eye that allow it to focus over varying
distances. They are the crystalline lens, ciliary
body, and the zonule.
The lens of the eye is a soft structure that gets progressively harder as we age. When
the lens is still soft, it can be made to change its shape. When it changes shape, it also
changes the distance at which the eye is focused. By age 40-45, the lens is starting to
become so rigid that it cannot change shape. The eye becomes fixed with one focusing
distance. Many adults need to start wearing glasses at is age to help them see clearly.
The ciliary body has several jobs. In this setting, the muscles inside the ciliary
body tighten and relax to cause the lens to change shape.
The zonule consists of small filaments that attach the ciliary body to the lens.
To focus from far to near, the ciliary body muscles tighten. This relaxes the tension
on the zonule. The lens gets thicker and focuses on objects closer to the eye. When the
ciliary body muscle relaxes, the zonule tightens, pulling on the side of the lens and
making it thinner. This allows the eye to focus on something further away.
Just as aging decreases our ability to accommodate, other factors can influence this
function. Various medicines can decrease the ability to focus. Ophthalmologists take
advantage of this when we give eye drops during an eye examination that relax these
muscles. This allows us to see what the eye's natural focusing ability is. Some illnesses,
such as diabetes, can also decrease our ability to focus.