Accommodation enables our eye to focus on objects close to us. Presbyopia represents the deterioration of this ability, which may ultimately lead to the need for reading glasses.
Accommodation
Like the lens of a camera, our eye has a built-in ability to focus, on one hand, on objects that are far from us, and on the other hand, also to adjust the focus so that we can see objects that are close to us. What allows us to do this is the ability of accommodation. The ability to perform accommodation depends on the eye's ability to increase the dioptric power of the eye's lens.
How is accommodation performed?
The ciliary muscle is attached to the zonules that are attached to the lens, and when it contracts (counterintuitively) it releases the tension of the zonules and the lens takes on a more spherical shape. A more spherical lens has a higher ability to concentrate light rays (a greater diopter).
The nerve responsible for the ability to perform accommodation is the oculomotor nerve, that is, parasympathetic fibers. Medications that relax the ciliary muscle are called cycloplegics.
When we are young, the ability of our eye to perform accommodation is very impressive (between 12-20 diopters), but as we age this ability deteriorates, and around age 40 significant difficulty in performing accommodation begins to appear, which manifests in the form of presbyopia.
Presbyopia
As explained earlier, when we are young our lens is very flexible and succeeds in changing shape in order to perform accommodation with a dioptric power of up to 20. Presbyopia is the impairment or loss of the ability to perform accommodation. By the fourth or fifth decade of life, the nucleus of the eye's lens is already hard and sclerotic and is not flexible enough to perform the curvature required for accommodation (the dioptric power drops to 2). Several studies indicate that the stiffness of the lens increases by 5-10 times over the course of life. Additional factors may also bring about these changes, such as a change in the point of attachment of the zonules on the lens over the years, changes in the size of the lens itself and more. If you feel a deterioration in the ability to read books, newspapers or anything else up close, it is advisable to visit your ophthalmologist at least once to see whether this is indeed the process described above and to determine the extent of the need for reading glasses.
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