Presbyopia

By Judith Lee and Gretchyn Bailey; reviewed by Dr. Vance Thompson

The eye's lens hardens with age, resulting in blurred near vision. (Illustration: Varilux)

During middle age, usually beginning in the 40s, people experience blurred vision at near points, such as when reading, sewing, or working at the computer. There's no getting around it - this happens to everyone at some point in their life, even if they never had a vision problem before.

Signs of Presbyopia When people develop presbyopia, they find they need to hold books, magazines, newspapers, menus and other reading materials at arm's length in order to focus properly. When they perform near work, they may have headaches or eyestrain, or feel fatigued.

What Causes Presbyopia Presbyopia is caused by an age-related process, rather than the way light is refracted, or bent, by the eye (which causes astigmatism, nearsightedness and farsightedness). Presbyopia is caused by a slow loss of flexibility within the lens inside your eye.

These age-related changes occur within the proteins in the lens, making the lens harder and less elastic with the years. Age-related changes also take place in the muscle fibers surrounding the lens.

Presbyopia Treatment Glasses with bifocal or progressive addition lenses (PALs) are the most common correction for presbyopia. Bifocal means two points of focus: the main part of the spectacle lens contains a prescription for nearsightedness or farsightedness, while the lower portion of the lens holds the stronger near prescription for close work.

Progressive addition lenses are similar to bifocal lenses, but they offer a more gradual visual transition between the two prescriptions.

Reading glasses are another choice. They may be worn just while doing close work, and may even be prescribed to wear over top of contact lenses (usually worn for distance correction). These glasses may be purchased over-the-counter at a retail store, or higher-quality versions may be prescribed by your eyecare practitioner.

There are contact lenses for presbyopes, called multifocal lenses. You can obtain multifocal contact lenses in gas permeable or soft lens materials. Another type of contact lens correction for presbyopia is monovision, in which one eye wears a distance prescription, and the other wears a prescription for near vision. The brain learns to favor one eye or the other for different tasks. But while some people are delighted with this solution, others complain of dizziness or nausea, or miss the depth perception they once had.

Because the human lens continues to change as you grow older, your presbyopic prescription will increase over time as well. You can expect your eyecare practitioner to prescribe a stronger correction for near work as you need it.

Surgery for Presbyopia By Frank Celia; reviewed by Dr. Charles Slonim

Even if you undergo LASIK or PRK as a young person and achieve perfect vision, you still will develop a condition called presbyopia as you grow older (typically beginning between the ages of 38 and 42). Presbyopia is the inability to focus on near objects that requires you to wear reading glasses or bifocals. Eye doctors disagree about what causes it; most believe it's caused either by stiffening of the eye's lens, continued growth of the lens or atrophy of the muscles controlling the lens, but other theories exist as well.

Although some surgeons will produce what is known as "monovision" during LASIK to enhance near vision, currently there is no device approved by the FDA specifically to treat presbyopia. However, there are several experimental devices and procedures that are under investigation. Here is a rundown of what the future could hold.

Monovision and LASIK One way eyecare professionals deal with presbyopia is by producing monovision. Normally, both your eyes work together equally when you look at an object, what's called binocular vision. However, you probably have a dominant eye that your brain tends to favor for "sighting" (most right-handed people are right-eye dominant, for example). Contact lens fitters often take advantage of this "one-eye dominance" to produce monovision (think of it as the opposite of binocular vision) with the contacts: they fit one eye for distance vision (typically the dominant eye) and one for near vision.

Therefore, in monovision, one eye does more work (sighting) than the other. If one of your eyes is farsighted and the other is nearsighted, the farsighted eye will do most of the work when looking at objects in the distance, and the nearsighted eye will do most of the work when looking at objects close by.

Some LASIK surgeons will produce monovision in their presbyopic patients by purposely leaving the non-dominant eye slightly nearsighted so that these patients can see up close without glasses (out of one eye). Many are wary of the technique because not everyone can become accustomed to the absence of binocular vision. It's better to try monovision with contact lenses first to be sure you can adapt.

Surgical Reversal of Presbyopia (SRP) With Scleral Expansion Bands (SEBs) This is the surgical technique generating the most excitement in the eyecare community. The surgeon inserts four plastic segments made out of polymethyl methacrylate (PMMA) just below the surface of the sclera, which increases the distance between the muscles that focus the lens and the lens itself. Researchers think the extra distance augments the tension of the muscle, thus allowing it to do a better job of focusing the lens. Investigators are still conducting trials on these devices, so it remains to be seen how well they work.

In May 2001, surgeons presented results of some SRP studies. One group found that their three patients had an average increase of 1.5 diopters (D) of accommodative amplitude. Another group found that their 10 patients had an average increase of 1.6 diopters after two years.

Overall, some eyes that have received the implants show improvement, and some do not. Also, critics have raised safety concerns. The implants may erode or expand over time, and they carry the risk of infection and of decreasing the blood circulation in the eye.

Anterior Ciliary Sclerotomy (ACS) In this procedure, the surgeon makes about eight incisions in a radial pattern on the sclera. ACS is based on the theory that presbyopia is caused by the continual growth of the lens throughout a person's lifetime. Eventually, according to this theory, when we reach a certain age, the lens has grown so much that it does not have room to change its shape. This shape change is a necessary step in focusing on close objects.

The incisions in ACS create more room for the lens to change shape. The procedure is not specifically approved by the FDA, but because it does not involve using any unapproved devices or drugs, it can be performed in the U.S. as an "off-label" procedure.

There are very few published results on ACS. Early studies found an average increase of about one diopter, but a later study found no prescription change at patients' one- and six-month follow-up visits.

Laser Presbyopia Reversal (LAPR) Laser presbyopia reversal involves using infrared lasers for scleral ablation. Similar to ACS, surgeons use the lasers to make eight spoke-like excisions in the sclera to thin it and give the lens more room to operate.

The company pioneering this new technology, SurgiLight, Inc., studied 100 eyes of 55 patients who had the procedure. Preoperatively, they all had near prescriptions of +1.5 D to +2.5 D, with an average improvement of 1.9 diopters after surgery.

Another study found that most patients' accommodative range increased by 1.00 to 2.50 diopters within two weeks of surgery. There was minimal regression 18 months later.

The company is currently conducting clinical trials and hopes to obtain FDA approval within one to two years.

Changing the Eye's Lens With Lasers While some surgeons work with the sclera, others think the lens might be the key to presbyopia surgery. They've proposed two techniques, but have not yet begun experiments.

The first, called photophako reduction (PPR), is based on the theory that presbyopia is caused by lens growth. PPR would use a laser to create cavities in the lens, thereby reducing it.

The second, called photophako modulation (PPM), is based on the theory that the lens becomes harder as we age. PPM would use a laser to create minute perforations in the lens to soften it.

Artificial Lenses Some companies are experimenting with removing the lens entirely and inserting an artificial one. In these procedures, the artificial lens is connected to the same muscles that controlled the natural lens. A company called C&C Vision is in the process of conducting preliminary studies on such an artificial lens.

If you know someone who's had cataract surgery, you may be wondering how the intraocular lenses cataract patients wear may be different from artificial lenses for presbyopia. In general, a person who has cataract surgery with an intraocular lens is never going to accommodate (focus on a near object) again with that eye. Whereas, with an artificial lens to correct presbyopia, the surgeon is trying to mimic the natural eye's ability to accommodate, which is not an easy task, because it involves muscles and the lens changing shape or at least changing position in the eye.

Today's Options None of these procedures is available right now except monovision LASIK and ACS. Getting monovision LASIK done before your presbyopia reaches its peak is not a good idea; presbyopia gets worse as we get older, but levels out at about +2 or +2.5 diopters between the ages of 50 and 65. A changing prescription would not be a problem with ACS, where the surgeon leaves enough room for the lens to change shape as the presbyopia progresses.

Some of the procedures that are still in investigational stages also allow for presbyopia progression. For example, with the scleral expansion bands, patients are given much more accommodation than they need to correct for the +2.5 diopters. They could be left with +10 to +15 diopters of accommodation if the surgery is done well. So no matter how much worse the presbyopia becomes, they should always have some diopter power "in reserve."