An Eye for An Eye, Health Matters, August 2011
Eyeglasses and contact lenses are a source of major inconvenience for millions of sight-challenged individuals. So when laser-assisted refractive surgery was introduced, many were ready to partake in the ophthalmologic version of "throwing away the crutches."
Near-sightedness (myopia), far-sightedness (hyperopia) and astigmatism are the three primary refractive errors that result from a distortion in the way light is bent as it passes into the eye. This distortion, usually caused by an imperfection in the shape of the cornea or the eye itself, leads to a blurry image at the back of the eye (retina).
Leland Rosenblum, MD, an ophthalmologist who practices at Monterey Bay Eye Center and serves on the Board of Directors of the California Academy of Ophthalmology, explains how light is bent at two distinct locations of the eye.
"The first is the cornea," Dr. Rosenblum says. "The second is the natural lens that sits behind the iris (the colored part of the eye). ... By reshaping the cornea, we can change how light is focused inside the eye and reduce dependence on glasses and/or contacts."
Photorefractive Keratectomy (PRK) and LASIK (Laser-Assisted In Situ Keratomileusis) correct refractive errors by reshaping the middle layer of the cornea (stroma). Though the end result is the same, they differ in the manner in which they expose the corneal stroma to the laser.
Philip Penrose, MD, who completed an ophthalmology residency at California Pacific Medical Center in San Francisco, performs LASIK and cataract surgery at Monterey Bay Eye Center.
"[With PRK], you rub off the superficial cells of the cornea, so you essentially have corneal abrasions," Dr. Penrose explains. The stromal layer is then vaporized with an excimer laser. With LASIK, the stroma is exposed by creating a flap in the outer corneal layer, usually utilizing a blade device (microkeratome) to make a precise incision. The flap is folded back, and the stroma is then vaporized with the same type of laser used in PRK.
In the case of PRK (performed when a higher degree of correction is needed or when a patient has thin corneas), the superficial layer grows back over a couple of days. With LASIK, once the flap is placed back into position, it adheres to the underlying tissue.
"With LASIK, I send people home to sleep for three hours," says Penrose, a member of the American Academy of Ophthalmology and American Society of Cataract and Refractive Surgeons. "When they wake up, the pain and irritation have passed. With PRK, it's a couple of days to get to that point, but you don't carry the risks of creating a flap."
Jon Page, MD practices at Vantage Eye Center, which has offices in Monterey and Salinas. A member of the American Academy of Ophthalmology and American Society of Cataract and Refractive Surgeons, Dr. Page, a cornea specialist, is familiar with the longer recovery time with PRK. He adds, however, that "four to six months later most studies show there's no difference in the final outcome between surface ablation [PRK] and LASIK."
To qualify as a candidate for laser refractive surgery, "The first thing you need is a healthy eye," Page says. "We also look at corneal thickness and shape and the patient's age. ... And you want to make sure their prescription has been stable."
As with any surgical procedure, risks must be carefully evaluated.
"During [LASIK]," Page says, "the complications we worry about are mostly those with the flap, which are quite rare, less than one percent. ... After the procedure, we worry about an infection within the flap (less than one percent), a malpositioned flap ... or inflammation underneath the flap. But with newer generation antibiotics and anti-inflammatory drops we rarely see these complications."
Some studies have shown that the risk of infection associated with contact lenses is higher than with LASIK, Page adds.
Other side effects that usually resolve over time include difficulty with night vision, dry eyes and light sensitivity. According to the American Academy of Ophthalmology, it may take three to six months for a person's vision to stabilize and the need for glasses or contact lenses may persist.
"LASIK corrects for distance, but ... patients have to understand they'll still need reading glasses," notes Penrose. "It's a great procedure for patients 21 to 50 ... if they have active lifestyles and don't need to do a lot of reading. But about two percent of patients need an enhancement at some point with LASIK or PRK."
Laser refractive surgery is not recommended for those with early cataracts, because the cataract may progress and interfere with vision. However excellent refractive results can be accomplished with cataract surgery in those whose cataracts are immature, says Rosenblum.
Cataract surgery has its attendant risks.
"In my hands, cataract surgery works abut 98 times out of 100," Rosenblum says. "But there's the rare possibility of infection inside the eye (less than one in a thousand), retinal detachment, unexpected bleeding, the need for additional surgery ... and loss of vision."
Specialty lenses that correct for distant and near vision, as well as presbyopia, are now available for implantation during cataract surgery. However, surgery for an immature cataract is usually not covered by insurance.
Wavefront-guided or Custom LASIK is an exciting development in laser refractive surgery that can provide slightly crisper vision and decreased incidence of glare and halos.
"We now use machines that measure not only near-sightedness and far-sightedness [lower-order aberrations], but also higher-order aberration," Page says. "It's like generating a fingerprint of your eye."
Whatever your refraction needs, your eye surgeon should have completed an ophthalmology residency and be certified by the American Board of Ophthalmology. When searching for a physician, inquire about the volume of surgery performed as well as complication rates. An additional year of training in a corneal fellowship (cornea specialist) is not a prerequisite for performing LASIK, but your surgeon should be certified in the use of the excimer laser and the microkeratome.