July 2013

 

COVER FEATURE

 

Cataract challenges

Cataract surgery in post-refractive surgery patients


by Michelle Dalton EyeWorld Contributing Writer

   
Eye after previous surgery

An eye after previous RK and LASIK surgery Source: Uday Devgan, MD

Performing complicated surgery doesn't have to be excruciatingif you are meticulous in preoperative stages

With the popularity of laser vision correction, it is extremely unlikely cataract urgeons will never encounter a patient who has undergone refractive surgery. But because the corneas of these patients have changed, planning for cataract surgery is a bit more complicated. "Most of our machines measure just outside this central area and then extrapolate values for the central cornea. This works well for virgin corneas, but not so well in eyes with prior LASIK, PRK, or RK," said Uday Devgan, MD, in private practice, Los Angeles, and chief of ophthalmology, Olive View UCLA Medical Center. (See "Calculating IOL power in post-RK eyes" for more on that topic.) Plus, surgeons need to consider both the anterior and posterior corneal curvaturesthe relationship between each changes depending on what type of refractive surgery the patient had, said Samuel Masket, MD, in private practice, Advanced Vision Care, Los Angeles. In myopic photoablative procedures, the anterior cornea is flattened but the posterior cornea remains unchanged (except in cases of ectasia), causing the preop near-parallel curves to take on a higher value than the assumed 6 D in an unoperated eye, he said. "When we read with a standard keratometer, we overestimate the corneal power in an eye that has undergone myopic photoablation," he said. Conversely, those same machines will underestimate the central corneal value in eyes that underwent hyperopic photoablation, Dr. Devgan said, and those values may be off by as much as 2 D.

"While manual and automated keratometry can provide reasonable starting values, we still need to use calculations to adjust for the prior keratorefractive surgery. Some machines like dual Scheimpflug imaging can give a more accurate central corneal power value, but even still the surgeon needs to factor in the prior keratorefractive surgery," he said.

Barry Schechter, MD, in practice, Florida Eye Microsurgical Institute, Boynton Beach, Fla., uses the Pentacam (Oculus, Wetzlar, Germany) to generate K readings on both the anterior and posterior cornea.

"I also use the Holladay formula, and it's been accurate about 85-90% of the time," Dr. Schechter said.

For Barbara Bowers, MD, in private practice, Innovative Ophthalmology, Paducah, Ky., "I'm a little obsessed with preop testing. I take readings from the Lenstar [Haag-Streit, Koniz, Switzerland], the Pentacam and AR Ks on all my cases, including the post-refractive patients," she said. "I've found the Lenstar to be the most accurate of any measurement. It's nice when they all line up and agree, but when they don't, I use the Lenstar." There's been "some dispute in the literature" about the reliability of "true" corneal power measurements obtainable with the Orbscan (Bausch + Lomb, Rochester, N.Y.) and the Pentacam in post-refractive eyes, Dr. Masket said.

Choosing an IOL formula

Once the preoperative readings are complete, there's still the issue of choosing a lens, and various formulas have various advantages. "The third generation IOL calculation formulae are remarkably similar other than the way they calculate effective lens position," Dr. Devgan said. "Use of the Aramberri Double-K method with a formula like the Holladay can increase our accuracy. It does this by using the measured K value for the IOL power calculation but then using a fixed, average value of about 43.5 for the determination of effective lens position. The third generation formulae (Hoffer Q, Holladay 1, SRK/T) all use the input K value to help determine lens position with a flatter K value indicating a likely shallower anterior chamber. This may hold true in virgin eyes, but in eyes where the central cornea has been flattened with LASIK, there is no change in the anterior chamber depth."

Dr. Bowers runs "multiple formulas on all cases (SRK-T, Holladay, Holladay 2, Hoffer Q), and with post-refractive patients I will use Aramberri Double-K modification to add or subtract power from the suggested power by these formulas." She also recommends running the same formulas using Holladay 2 with pre-refractive surgery data plugged in. In post-hyperopic refractive patients, she'll use the current refraction because of the regression issue. Lastly, she'll run the Hill/ ASCRS program.

"If I had to pick just one formula, I'd probably use the Hill/ ASCRS site," she said.

Dr. Schechter uses "straight Ks from the Pentacam" in post-hyperopic LASIK patients, and advises surgeons to check against the original K readings whenever possible. "We use the Masket formula and sometimes the Feiz-Mannis method just to compare," he said.

Dr. Devgan said the newer generation formulaeHaigis-L and Holladay 2include data such as measured anterior chamber depth and white-to-white, among others, to increase accuracy of the predicted effective lens position after cataract surgery. (Haigis-L is not recommended for prior RK or for hyperopic treatments, however.) "I take a different approach to determine IOL power after myopic LVC," Dr. Masket said. " If he knows what LVC was performed, he uses his own formula (available on the Lenstar). (See sidebar for comparison on various methods.) If he doesn't know, "we rely heavily on the Haigis-L, True Corneal Power from Optovue [Fremont, Calif.], and intraoperative aberrometry ORA [WaveTec Vision, Aliso Viejo, Calif.]. Although we have not adapted the Shammas formula [Haag-Streit], we understand it is also reliable in this situation and we will be adding that to our regimen in the near term,"Dr. Masket said.

Premium lenses

Article summary

People who have already undergone refractive surgery have shown their motivation for spectacle-free living, and most are not deterred just because they have a cataractin fact, some clamor for multifocal IOLs. "Always look for higher order aberrations (HOAs) to see if there's a prolate cornea in these eyes," Dr. Schechter said. "Whenever you're doing multifocal (MF) lenses the expectations are higher, and in post-refractive cases you need to ensure patients understand it's not the same type of procedure as their refractive surgery was. They need to understand they may not be candidates for a multifocal lens. I always give them reduced expectations." Type A personalities are among those he tries to steer away from MF implantation.

Added Dr. Devgan: "If the patient has had a milder degree of prior refractive surgery and the cornea is regular and symmetric without excessive HOAs, then MF IOLs can work just fine." He cites decentered ablations and "a lot" of induced HOAs from a large degree of prior excimer treatment as exclusionary factors.

Dr. Bowers has no qualms about using MF lenses in post-refractive patients. "I've always had very good luck and these are some of my happiest patients," she said. "I aim for plano, but try to pick a lens power that will leave them slightly myopic instead of hyperopic. If there is a refractive surprise, laser enhancement is more predictable and stable with residual myopia than hyperopia. I spend a lot of time with preop patient education on the increased chance that they might need an additional procedure to 'tweak' or 'fine tune' their results because of the previous surgery," she said. Dr. Masket isn't as uniform in his decisions, weighing the time since laser vision correction equally with HOAs to make the determination. "If it's very old style laser surgery, which induced much positive spherical aberration, or if the patient has a high amount of HOAs, I avoid MF lenses," Dr. Masket said. "However, these are a very motivated group for spectacle independence, so I take that into account as well." He evaluates the optical zone size and pupil size, noting that MF lenses will only exacerbate existing night vision issues. "We don't want to introduce new sources of aberrations," he said.

Editors' note: Dr. Bowers has no financial interests related to this article. Dr. Devgan has financial interests with Aaren Scientific (Ontario, Calif.), Alcon (Fort Worth, Texas), Bausch + Lomb (Rochester, N.Y.), Gerson Lehrman Group (New York), Accutome (Malvern, Pa.), and LensGen (Irvine, Calif.). Dr. Masket has financial interests with Alcon, Bausch + Lomb (Rochester, N.Y.), Haag-Streit, Ocular Therapeutics (Bedford, Mass.), PowerVision (Belmont, Calif.), and Carl Zeiss Meditec (Jena, Germany). Dr. Schechter has financial interests with Bausch + Lomb and Omeros (Seattle).

Contact information

Bowers: barbbowersmd@comcast.net
Devgan: devgan@gmail.com
Masket: sammasket@aol.com
Schechter: bdsch77@aol.com

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