Often a dreaded reality of life for many an adult patient is the inevitable onset of the condition known as presbyopia. For most adults this is their first look down the barrel of mortality. Presbyopia aka "middle age vision" infers the unpleasant thought of a necessary and subsequent move away from their single vision eyeglass or contact lens correction, which the patient has known for years, into a bifocal. Yes, gone is the carefree innocence of young adulthood, from that day forward vision correction becomes more of a challenge. To begin to understand this change called presbyopia one must first discuss two things, the crystalline lens and accommodation.  

The crystalline lens [the lens] is a transparent biconvex structure that can change its shape. Imagine a large aspirin enclosed in a terribly thin elastic capsule, this is your lens. The lens is suspended in a clear fluid called aqueous humor by many fine fibers called zonules. The zonules run 360 degrees around its circumference, attaching at its edge or equator. The other end of the zonules insert into a radial muscle located just behind the iris, called the ciliary body. The crystalline lens lies directly behind the iris [the colored part of your eye] and is centered perfectly within the pupil. The lens has no blood supply nor innervation meaning there are no blood vessels or nerve fibers within it. It is a living avascular structure and receives the nourishment it needs to stay transparent from the fluid that surrounds it. If the crystalline lens is injured by chemical, mechanical, radiation, or by electrical means a cataract may result.  

Accommodation [the process of actively focusing] is usually an effortless process that results in the crystalline lens changing its shape and the eye changing its focus from far to near. When the patient views a near object the radial muscle called the ciliary body located just behind the iris contracts. This allows the zonules to relax and the elastic lens capsule to become rounder or bulge in the center. This small subtle movement allows the power of the young eye to increase dramatically. One might imagine a puppet on a string. As the puppeteer pulls on the strings the puppet moves. Similarly, as the ciliary body muscle contracts and relaxes, the zonular fibers move the elastic capsule surrounding the lens thereby affecting its movement and thus its power. There are two parts to accommodation. One is physical and the other is physiologic.  

Presbyopia results in the hardening of the lens which in turn reduces the elasticity of the lens capsule. This physical change in the lens due to ageing is what reduces accommodation. The physiologic part of accommodation is the strength, or lack thereof, of the ciliary body muscles ability to contract. Presbyopia is the natural loss of the ability to focus for near objects over many years. Most believe it is the physical hardening of the lens which contributes the most to presbyopia.  

The young child has a tremendous ability to accommodate. By the time you reach seventy five years old you will have zero accommodation. For many patients presbyopia will begin at or around forty five years of age. With this in mind consider Jacobs Optometry the next time you need to evaluate your presbyopia. Our multi-focal contact lenses for the correction of presbyopia may be just what the doctor ordered? So folks, if you need stronger bifocals or perhaps after receiving your very first bifocal, think of your crystalline lens. For if your lens was a clock surely it would be ticking. Can you here it ticking...