Presbyopia, sometimes called age-related farsightedness, is a visual condition causing a gradual loss of the eyes dynamic ability to focus at near range known as accommodation. It is the one ocular condition that is certain to affect all those who approach the age of fifty. Billions of people worldwide currently struggle with this inevitable condition, yet the exact process by which accommodation is lost is still not fully understood. The ability to shift focus from distant objects to near is called accommodation which is achieved by changing the shape of the internal crystalline lens of the eye. This lens is attached to an encircling muscle called the ciliary body via specialized tendon-like fibers known as zonules.
During accommodation the ciliary body contracts causing the crystalline lens to widen from lack of zonular tension. This widening effect or elongation of axial length causes an increase in lenticular power and a shift of focus from distant objects to near. Conversely, when accommodation is released, the ciliary body relaxes introducing zonular radial tension to the crystalline lens. This tension pulls the lens taught making the lens thinner and less powerful which returns the visual focus to the distance.
An analogy to visualize how the accommodative process works may be helpful in understanding the mechanism. A round trampoline works in a similar fashion to the accommodative function of the eye where the trampoline mat is the crystalline lens, the springs are the zonules and the aluminum frame is the ciliary body. If the aluminum frame were able to contract and constrict, as does the ciliary body, it would reduce in circumference thus causing the springs to lose tension and cause the trampoline mat to sag towards the ground. This movement or elongation of the mat is similar to the widening of the crystalline lens during accommodation. Now, if the frame were able to relax and stop contracting this would increase the circumference back to its normal size. That increase in circumference would cause the springs to once again tighten radially eliminating the sag in the mat as it once again becomes taut. During accommodation, this relaxation of the ciliary body and tightening of the lens will return focus back to the distance. Although the process of accommodation is well understood, the physiology of losing accommodation with age is more vague. Presbyopia usually begins in the fourth decade of life manifesting as a gradual loss of near focus. The most commonly accepted theory for presbyopia is that the crystalline lens loses flexibility and becomes more rigid with age. This inflexibility inhibits the lens from widening to increase power resulting in limited near vision.
Research has also suggested that aging causes the ciliary body to fatigue and the zonular fibers become more rigid. These factors may also contribute to the loss of accommodation as presbyopia progresses. Someday presbyopia may be fully understood and a cure discovered, but until then many treatment options are currently available to achieve better near vision for those over forty. The most simple and effective treatment utilizes reading glasses to see clearly at near range. Reading glasses, sometimes called readers, cheaters, or magnifiers, is an inexpensive treatment options that are readily available from gas stations to optometry offices. Reading glasses simply increase the power of the crystalline lens after it becomes inflexible and unable to elongate on its own. Bifocal glasses or multifocal contact lenses can also be used to successfully mitigate the effects of presbyopia.
In recent years, surgical treatment of presbyopia has increased in popularity for those seeking a more convenient and lasting solution. These procedures include monovision with LASIK/PRK, corneal inlays, and refractive lens exchange (RLE) procedures. Each procedure differs in risk, effectiveness, and cost. However, all have been proven to be efficacious and convenient alternatives to reading glasses. Due to its all encompassing nature, presbyopia is something that everyone should understand. A knowledge of what is occurring as presbyopia begins can alleviate much worry and apprehension felt by many as near vision starts to decline.
