Surgeons: Previous refractive surgery presents challenges in cataract

Three experts discuss how new methods and technologies help to eliminate refractive surprises and result in good outcomes.

Accurate IOL calculations are essential to optimizing the refractive outcomes of lens implantation after cataract surgery, according to three surgeons.

Challenges are arising as more patients who previously underwent refractive surgery are now undergoing cataract surgery. However, emerging technologies and methods may enable surgeons to make intraoperative IOL calculations that eliminate refractive surprises, the experts said.

In telephone interviews with Ocular Surgery News, OSN Optics Section Editor Jack T. Holladay, MD, MSEE, FACS, and cataract surgeons Sherman W. Reeves, MD, MPH, and Karl G. Stonecipher, MD, discussed the complex, painstaking process of making IOL power calculations that yield the best possible refractive outcomes. They noted key factors and common pitfalls that affect outcomes, especially in eyes that have had refractive surgery.

Key measurement parameters include keratometry, axial length, lens constants and, in cases involving previous refractive surgery, refractive history.

Jack T. Holladay

“IOL power calculations today have moved to a new level of standard of care, which includes three things: an axiometer with the IOLMaster (Carl Zeiss Meditec), back-calculating your personalized lens constant and good K readings,” Dr. Holladay said.

Premium IOLs require extensive preoperative calculation, Dr. Stonecipher said.

“Basically, the patient comes in, and we determine whether or not they want a premium lens,” he said. “If they want a premium lens, then we do a lot more workup than we do on the average patient.”

Tempering patients’ expectations is critical, Dr. Reeves said, citing the complexity and unpredictability of calculating IOL powers for patients who previously had refractive surgery.

“The most important thing, clearly, is to warn the patient that this is a far less accurate process than is standard for regular cataract surgery on a virgin eye,” Dr. Reeves said.

RK spurs hyperopic drift

An increasing number of patients who have undergone refractive surgery, particularly radial keratometry, are having cataract surgery, Dr. Holladay said.

“Unlike LASIK and PRK, RK in many patients has a long-term hyperopic drift that never stops, and in some patients you see a fluctuation from morning to afternoon in their refraction,” he said. “So all of these factors influence the outcome.”

The historical method of using RK patients’ refractive history does not account for changes in the crystalline lens, resulting in refractive surprises, he said.

“If the cornea gets a hyperopic drift and the lens is changing in a myopic direction, you may think there’s no change because they cancel each other out, and you come up with this big refractive surprise because there was a lenticular change,” Dr. Holladay said.

A modified historical method is slightly more accurate but has some limitations, he said.

IOL calculations after LASIK or PRK

Dr. Reeves was more optimistic about using the historical method as a reliable tool for making calculations in eyes that have undergone previous myopic LASIK or PRK.

“On average, when used with the Holladay 2 formula, we’ve found it returns results pretty close to plano and has a fairly small – within 0.75 D to 1 D – standard deviation, so that’s one we always try to calculate if we have previous refractive data from before the refractive surgery,” he said.

Dr. Reeves also pointed out that refractive errors after cataract surgery in these patients have generally been moderate among the surgeons in his practice, usually within about 1 D of plano.

“Though sometimes you can get a very high refractive error, 3 D or 4 D of error; that’s by far the exception,” Dr. Reeves said.

He said he uses several methods of calculating IOL power after refractive surgery.

“By taking a lot of different methods of calculating the post-refractive surgery IOL power and throwing out the far outliers, we usually end up fairly close to where we want to be,” Dr. Reeves said.

Emerging technologies

A new device from Wavetec, an intraoperative aberrometer after lensectomy, may help eliminate refractive surprises and reduce the need for additional office visits to exchange IOLs, Dr. Holladay said.

“There’s no question that intraoperative measurement of the refraction before and after the IOL is implanted will start to happen,” he said. “It will eliminate refractive surprises, particularly in those patients that we have so much trouble with that have had refractive surgery.

“Certainly that’s the next step,” he said. “After you’ve put an implant in the eye, on the table during surgery you can measure their refraction. So you’re not going to have any big surprises anymore because that will eliminate that. It’s a great idea.

“The goal is to see if we can do it with the aphakic refraction, measure the patient before we put the lens in,” he said. “Our hope is that the aphakic refraction is better so that it reduces the chance of having to exchange the lens. That’s the hope, but we haven’t proven that yet.”

Dr. Reeves cited encouraging results of studies on intraoperative refraction, retinoscopy and autorefraction, and pointed to the potential benefits of intraoperative measurement.

“It would certainly be helpful to have an instrument or device that could intraoperatively measure what power lens should go into the eye right in the operating room,” he said.

Light-adjustable IOLs also offer promising results, even after cataract surgery, Dr. Reeves said.

“That is also going to be very helpful because if there is some refractive error that you end up with, postoperatively being able to tune that intraocular lens after you’re out of the operating room could also help solve any problems that you end up with,” Dr. Reeves said.

Dr. Stonecipher noted the utility of various online resources designed to facilitate IOL calculation, such as the Holladay IOL Consultant, which he uses in conjunction with the Pentacam (Oculus), the ASCRS Web site for intraocular power calculations after previous refractive surgery and DataLink, a tool sponsored by eyeonics.

“In lieu of intraoperative measuring devices available in a surgical setting at present, I immediately refract difficult patients postoperatively to ensure my lens is within an acceptable standard,” Dr. Stonecipher said. “With modern surgical techniques, obtaining a reliable refraction is possible immediately after the patient has had surgery.”

Keratometry values critical

The keratometry reading is the most critical factor influencing the accuracy of refraction in patients who have undergone refractive surgery, Dr. Holladay said. In fact, faulty keratometry readings lead to refractive surprises and require IOL replacement or refractive enhancement later, he said.

Karl G. Stonecipher

“In patients that have had refractive surgery, the K reading is the variable that makes the biggest refractive surprise,” Dr. Holladay said.

Several instruments help surgeons deal with various hurdles. For example, the Pentacam allows direct measurement of the cornea and requires no historical data on refraction.

Keratometry readings taken with the Pentacam are used to make IOL calculations for patients who have undergone PK or LASIK, Dr. Holladay said.

“For accuracy in these post-refractive surgery patients, most critical is the K reading,” he said.

Dr. Holladay cited one study in which a comparison of historical keratometry values and actual values for LASIK patients showed a standard deviation of 0.54 D. Another study using the Holladay IOL Consultant to back-calculate keratometry readings showed a standard deviation of about 0.95 D, he said.

“Prior to that, the error was maybe up to 3 D,” Dr. Holladay said. “So it’s not as good as the 0.5 D that we got with the LASIK peer study with the cornea, but it is something that’s far better than what we’d been able to do in the past with historical methods that are all over the place, because you never know what’s going on with the lens inside the eye. Particularly with an RK person, it’s been many years.”

Dr. Stonecipher said he uses the Nidek OPD-Scan II, a wavefront aberrometer that uses skiascopy, and the Pentacam.

“The reason I’m using the Nidek OPD is because that allows me to see how much of the astigmatism is related to the cornea and how much of the astigmatism is related to the lens,” he said.

Axial lengths, lens constants

Drs. Holladay and Stonecipher also pointed to the IOLMaster, which uses laser interferometry instead of ultrasound to measure axial length. The device does not require a clinical corneal history.

“Length measurements are unquestionably best with the IOLMaster today, using light rather than ultrasound,” Dr. Holladay said. “They’re much more accurate so that’s become the standard of care for patients that you can measure. That’s critical.”

Dr. Stonecipher called the IOLMaster the “most accurate way” to measure axial lengths in post-refractive patients, although he uses immersion in some patients. In his office, outcomes comparing the two methods favor the IOLMaster for predictability, he said.

“In terms of results, basically what’s helping me most is being consistent with the K reading, which I’m getting mainly off my Pentacam, using the software provided by Dr. Holladay on the Pentacam plus the Holladay IOL Consultant and the IOLMaster combined,” Dr. Stonecipher said. “Usually, I’m looking at the Holladay analysis on the Pentacam and that helps me pick my K readings. I’m looking at the Pentacam K readings and using the IOLMaster as the actual axial length measurement.”

Dr. Reeves said he uses immersion ultrasound to measure axial length.

“For our standard cataract patient, we use immersion ultrasound, and I think that’s sort of the universal standard,” he said. “That and also the IOLMaster. Either one of those two should be used for optimal axial length measurements.”

Dr. Holladay advised surgeons to personalize lens constants.

“If you want good results, you need to do those two things,” he said. “I can’t stress enough how important it is for surgeons to personalize their lens constants. It’s so simple. You just put in the postoperative refraction when the patient is done, and the programs and the software out there will calculate for you. It eliminates the surprise that happens in unusual eyes because you’ve got your own constant.”

Dr. Stonecipher noted that he diligently monitors lens constants throughout his practice.

“The quality of the person doing the IOLMaster is important, too,” he said. “So I’ve got two technicians, and that’s all they do. I’m constantly looking over their shoulders. I’m constantly re-evaluating my surgeons’ constants and basically refining my outcomes as best I can.”

For more information:

• Jack T. Holladay, MD, MSEE, FACS, can be reached at Holladay LASIK Institute, Bellaire Triangle Building, 6802 Mapleridge, Suite 200, Bellaire, TX 77401; fax: 713-668-7336; e-mail: holladay@docholladay.com.
• Dr. Holladay is a consultant for Oculus, Nidek and Advanced Medical Optics. Sherman W. Reeves, MD, MPH, can be reached at Minnesota Eye Consultants, 710 E. 24th St., Suite 106, Minneapolis, MN 55404; 612-813-3687; fax: 612-813-3649; e-mail: swreeves@mneye.com.
• Dr. Reeves has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned. Karl G. Stonecipher, MD, can be reached at Southeastern Laser and Refractive Center, 3312 Battleground Ave., Greensboro, NC 27410; 336-282-5000; fax: 336-282-5022; e-mail: stonenc@aol.com.

• Matt Hasson is an OSN Staff Writer who covers all aspects of ophthalmology. He focuses on regulatory, legislative and practice management topics.