The perfectly focusing eye is an emmetropic eye. Light enters the eye and is sharply focused on the retina. Nerves send the retinal images to the brain and this perfect eye system sees 20/20.
You may be familiar with the term myopia, also known as near-sightedness. Myopia is the result of an eyeball which is too long, or a cornea which is too curved. In both cases, light rays entering your eye fall short of the retina, and objects in the distance appear blurred. If you have this condition, you are not alone; more than 70 million people in North America have myopia.
Hyperopia, also known as farsightedness , is a defect of vision caused by an imperfection in the eye (often when the eyeball is too short), causing inability to focus on near objects. As an object moves towards the eye, the eye must increase its power to keep the image on the retina. If the power of the cornea and lens is insufficient, as in hyperopia, the image will appear blurred.
Astigmatism occurs when your cornea is shaped like a football with two different curvatures. Images appear blurred or ghost-like because light rays are refracted unequally. In extreme cases, images both near and far, appear blurred. Many people who have myopia also have astigmatism.
Presbyopia affects everybody around age 40 and thereafter. Current refractive surgery, including PRK and LASIK, do not cure it. Presbyopia refers to the eyes’ diminishing ability to focus up close with age. For patients in the 20’s and 30’s, presbyopia is often difficult to understand. If this applies to you, one of the best ways to understand presbyopia is when your eyes are dilated at your eye care providers office. The dilating drops simulate presbyopia by relaxing your eyes’ ability to focus (besides making your pupils large). If you wear glasses to see clearly far away, put them on when your eyes are dilated. Then try reading. It’ll be hard to focus, and this is what presbyopia is like!
Another way to understand presbyopia is as follows. Young emmetropes can usually clearly focus on objects right up to their nose. Yet with time, this point of near focus moves progressively further back. Usually in the early 40’s, this point of near focus is at arm length, and it becomes difficult to keep things clear. This is when most people get reading glasses. Every few years, the reading prescription will change because the focusing ability continues to decline until around age 60 when there is almost no more to lose.
Emmetropes usually notice presbyopia around age 40. However, patients with hyperopia tend to notice presbyopia earlier than emmetropes. This is because hyperopes expend part of the focusing ability just to see clearly far away. On the other hand, patients with a small amount of myopia tend to notice presbyopia later than age 40 because their eyes have a “built-in” reading prescription which allows them to read more comfortably without their glasses or contacts.
TREATMENT OF PRESBYOPIA
Presently, there are several investigational treatments emerging for presbyopia. Although there is still debate over what causes presbyopia, studies clearly indicate that with age, the crystalline in the eye hardens and loses elasticity. This process is responsible for at least some, if not all, of presbyopia. Ronald Schachar, M.D., Ph.D., has proposed an alternate hypothesis stating that presbyopia is mostly due to a slackening of fibers that transmit force to change the crystalline lens shape. This hypothesis is controversial, yet may have some merit. Ultimately, successful presbyopia-reversing surgery will require a technique that addresses the actual cause. The market potential for such a treatment is enormous because with enough age, everybody becomes presbyopic.
The most publicized technique is the Surgical Reversal of Presbyopia (SRP) under development by PresbyCorp. This technique assumes that presbyopia is due to slackening of fibers attached to the lens. By using four “scleral expansion bands”, this procedure supposedly makes these fibers taut again, restoring the ability to change focus. To-date, over 500 SRP procedures have been performed worldwide with mixed results. Clinical trials are just beginning in the United States at six centers. The trials will provide information to evaluate the safety and efficacy of SRP. There are some concerns about the procedure’s safety, including the risk of perforating the globe, erosion of the expansion bands, infection, and decreasing blood circulation in the eye. This procedure is performed in Mexico and other countries outside the U.S. despite a poor characterization of this procedure’s safety and efficacy.
Another procedure, called Anterior Ciliary Sclerotomy or ACS, also supposedly makes the fibers attaching to the lens taut. ACS involves placing several partial thickness incisions on the sclera or white part of the eye in a radial pattern, somewhat reminiscent of radial keratotomy. Circumstantial reports suggest this procedure can restore the ability to change focus for several weeks before completely regressing to the preoperative state. Some surgeons are experimenting by placing silicone implants inside the radial incisions, trying to prevent the regression.
An important note from Dr. Thompson:
See: Risks of Refractive Surgery. Remember surgery is surgery and all surgery has risks. This is not meant to discourage you but these are facts you should know if you plan to have surgery preformed. This office is extensively involved in refractive surgery and would be happy to meet with you and discuss your case. I have personally had refractive surgery. But, just because these risks were acceptable to me does not mean they will be acceptable to you. I strongly recommend you educate yourself prior to surgery and then consult a knowledgeable eye care provider to further guide you through the procedure and follow-up. Pre and post operative care is critical in maximizing your chance of a good outcome.
Our office policy is to educate our refractive surgery patients well enough that they have realistic expectations and know the risks before they commit to the surgery, we believe in informed consent. Once the decision is made, it is our goal to get that person to the best surgeon for the amount of money they want to spend.