September 2011

 

REFRACTIVE SURGERY

 

Age, degree of correction determine surgery choice for myopes


by Jena Passut EyeWorld Staff Writer

   

Experts agree those are top considerations before LASIK, PRK, or RLE, but other factors come into play, too

The age of the patient and degree of myopic correction are two factors that sway a surgeon's decision when choosing between PRK or LASIK and refractive lens exchange, according to practitioners who recently spoke to EyeWorld on the subject.

The first factor a surgeon should evaluate in the myopic patient is the degree of correction, said Y. Ralph Chu, M.D., Bloomington, Minn.

"That puts patients down a certain path as to whether they're good candidates for laser vision correction of the cornea or if they need an alternative procedure like a refractive lens exchange or a phakic IOL," Dr. Chu said.

Even more important to Dr. Chu, however, is the patient's age when determining whether to perform RLE.

"I think it's important, as a surgeon, to talk to people who are older," he said. "Even if they have healthy eyes, LASIK may work and help distance vision, but it won't help near vision. There are other technologies such as lens implants that we put in through refractive lens exchange that could help on the distance, near, and intermediate vision."

Other factors also come into play, including Snellen acuity, quality of vision, contrast sensitivity, and new lens technologies.

"New presbyopia-correcting lens implants give a larger range of focus for some patients in the older range group," Dr. Chu said. "I still try to base (my decision) on what is going to give the patient the best possible visual outcome."

In higher degrees of correction, which Dr. Chu defines as more than 6 of myopia or 3 D or 4 D of hyperopia, surgeons should consider thickness of the cornea, ocular surface health, and aging of the lens. "With higher degrees of correction, the issue becomes quality of vision and loss of contrast," Dr. Chu said. Neel R. Desai, M.D., Largo, Fla., said both age and degree of correction are main factors when deciding on which procedure to use. However, if a patient is already presbyopic or pre-presbyopic, he tends to steer him or her toward RLE for several reasons.

"One (reason) is that they are already experiencing what that loss of near vision is like," he said. "They are familiar with that, and it makes my targeting after a refractive lens exchange that much easier, in case they end up not at J1 at near, but at J3 or J5, which is achievable with any number of the presbyopic correcting lenses. (RLE) also saves them (cataract) surgery later on down the road. When all their friends are 60, 65, or 70 and having cataract surgery, they've already had their procedure done and have a longer time to enjoy their good vision."

A younger patient ends up in a gray zone, and then the cornea and degree of correction helps Dr. Desai decide on a course of action. "If he or she is a very high myope with perhaps a borderline cornea, which I will kind of grossly define as a predicted stromal bed of less than 300 microns, where there are unusual topographies, certainly I am going to steer that patient toward advanced surface ablation or PRK," he said. "If the patient is a little bit older than that and he has a suspicious looking cornea, I'm going to leave the cornea alone and not risk ectasia or an unpredictable outcome. I would go ahead and do a refractive lens exchange, get him to a good distance target and then, if needed, I can do a small laser vision correction enhancement after the RLE."

For those patients above 40, Dr. Desai said he does contact lens trials, often with cycloplegia, to simulate the refractive outcomes and targeting options after LASIK, PRK, or RLE in this pre-presbyopic group.

Louis E. Probst, M.D., national medical director, TLC Laser Eye Centers, prefers PRK or LASIK for treating myopia. "I personally only use PRK up to 6 of correction, simply because I've found the accuracy and healing is more variable in higher levels of correction with PRK, or approximately 100 microns of depth," Dr. Probst said. "I use LASIK up to the maximum custom ablation, which is usually somewhere around 11 or 12. That's assuming the eyes are healthy and there's no contraindicating factors or risk factors for ectasia."

Other factors he considers include the amount of posterior stromal tissue, the size or depth of ablation, and possibly the age of the patient, he said. "For the vast majority of patients, LASIK can be performed for high myopia," he said. "LASIK is much more convenient since it can be done bilaterally in a laser center setting and much safer in general compared to phakic IOLs, which are intraocular surgery and involve intraocular complications. Because it's not a laser procedure, it's a lens procedure, it does not have the higher accuracy we are able to achieve now, particularly with custom ablations."

The decision on whether to perform RLE is complicated by reports that retinal detachment rates could be as high as 8-10% in high myopes, Dr. Probst said. "That has been challenged in literature," he said.

In fact, in a 2004 study co-authored by Dr. Probst, researchers found an annual retinal detachment rate of 0.52% in 972 post-op cataract patient eyes. The 10-year retrospective study from 1993 to 2003 of moderately to highly myopic eyes with axial lengths greater than 25 mm found an overall detachment incidence of 1.3% over an average follow-up of 31 months.

Another study co-authored by Dr. Probst and Paul Ernest, M.D., Michigan, found a 0.32% annual risk of retinal detachment following lens replacement surgery. The 20 year retrospective patient review of 576 cataract cases with axial lengths of at least 25 mm found a 3.22% overall patient risk for developing retinal tears and detachments, compared with a 3.1% incidence before surgery.

"The rate of retinal detachment did not change," Dr. Probst said. "The surgery itself was not something that was causing retinal detachment. Similarly, Thomas Neuhann published a paper with the very same conclusion that the rate of retinal detachment in high myopes is higher than the general population, but doing cataract surgery with modern techniques does not change that rate."

Despite the research reports, Dr. Probst said surgeons should be aware that detachment rates are higher in high myopes. "When surgeons are considering a refractive lensectomy, they have to be concerned about this potential risk of retinal detachment, even though they may not be changing the actual rate of it," he said. Dr. Probst advised that patients should have a retinal examination prior to a procedure to document any possible predisposing factors for retinal detachment.

"If they see any tears or holes, those can be prophylactically treated with a retinal laser to weld the retina down to prevent that from happening," he said. A young patient with a healthy cornea is a top candidate for LASIK, Dr. Probst said. "There's no procedure that could possibly match the safety profile and the accuracy," he said. "We're always going to do LASIK if we can because of the advantages of it. The others only become considerations when you can't."

There is one factor when deciding on surgery that is far more important than age or degree of correction, Dr. Desai said.

The most important factor for any procedure, be it laser vision correction, refractive lens exchange, or refractive cataract surgery, is the patient, he said. "We have to be intimately familiar with the patient's visual needs and lifestyle and make decisions based on that. It's never going to be just based on the cornea or age or degree of correction. It's all of these factors combined with a good assessment of the visual needs and lifestyle."

Editors' note: Dr. Chu has financial interests with Bausch & Lomb (Rochester, N.Y.) and Abbott Medical Optics (Santa Ana, Calif.). Dr. Desai has financial interests with Alcon (Fort Worth, Texas), Allergan (Irvine, Calif.), Bausch & Lomb, Bio-Tissue (Miami, Fla.), Inspire Pharmaceuticals (Raleigh, N.C.), WaveTec Vision Systems Inc. (Aliso Viejo, Calif.), and TruVision (Santa Barbara, Calif.). Dr. Probst has no financial interests related to his comments.

Contact information

Chu: 952-835-0965, yrchu@chuvision.com
Desai: 727-518-2020, desaivision@hotmail.com
Probst: 708-562-2020, leprobst@gmail.com