Cataract Surgery Report

The emerging challenge: post-refractive cataract patients

Accurate IOL calculation is the primary issue.

By Jerry Helzner, Senior Editor

Increasing numbers of people who were part of the first wave of LASIK and PRK patients in the mid-to-late 1990s are now well into middle age and beginning to appear in ophthalmologists’ offices as candidates for cataract surgery. They represent the vanguard of what one cataract surgeon has described as “a multi-million patient issue.”

These patients present a problem to surgeons because achieving accurate IOL calculations in post-refractive eyes is difficult despite efforts to upgrade calculation formulas and introduce new technologies.

As Lawrence Brierley, MD, of Victoria, B. C., stated in his new study of post-refractive patients undergoing cataract surgery, “laser-based ophthalmic procedures change the natural spatial relationship between the anterior and posterior corneal surfaces, negating much of the value of the keratometric index of refraction.”¹

Still investigational in the United States, the Calhoun LAL is seen as a potential solution for post-refractive cataract surgery patients.

What’s more, the overall profile of this patient cohort, the early adopters of laser refractive surgery, is a group of individuals who have already demonstrated they place a priority on achieving excellent vision and are willing to pay for it. They will expect the same kind of outcome from their cataract surgery.

This article will discuss the challenges that post-refractive patients present to the cataract surgeon while offering several current — and potential — methods to minimize the problems of achieving accurate IOL calculations.

The future is now

It doesn’t seem long ago that millions of (mostly) myopes followed the lead of such celebrities as golfer Tiger Woods and model Cindy Crawford and rushed to have that “amazing” LASIK vision procedure everyone was talking about. LASIK advertising in the late 1990s almost universally promoted the “Wow” factor of patients walking out of surgery with perfect vision. What the advertising did not discuss much at the time was that laser refractive surgery was not going to prevent these patients from developing presbyopia and, then later, be vulnerable to cataracts when they reached their 50s and 60s.

Almost 20 years has gone by since that first group of early adopters rushed to have LASIK, Now, some of them are showing up needing cataract surgery. What’s a surgeon to do?

IOL CALCULATION CHALLENGES

Results vary among formulas

An interesting study presented at the recent ARVO meeting and conducted by Li Wang, MD, PhD, and Douglas Koch, MD, both of the Cullen Eye Institute of the Baylor College of Medicine in Houston, evaluated several of the newer IOL calculation updates to assess their accuracy.² Their study found that an OCT-based IOL calculation formula produced the lowest refractive mean absolute error of 0.41 D, followed by the Haigis-L formula (0.44 D), Shammas (0.51 D), Wang-Koch-Maloney method (0.57 D) and Galilei (0.65 D).

Drs. Wang and Koch also evaluated the ORA (WaveTec, Aliso Viejo, Calif.), which is unique in that its calculations provide intraoperative refractive information. However, WaveTec disputed the initial study results that show an 0.69 D predictive error in 15 eyes that underwent cataract surgery at Baylor.

Fine tuning calculations with ORA

In discussing the study findings with WaveTec, Dr. Wang says, “In our earlier dataset, the performance of this device (ORA) was not better than other devices. One reason might be that we were then using tetracaine (anesthetic), which is toxic to the cornea and could alter corneal curvature and accuracy of measurements. Since we have stopped using tetracaine, our impression is that our ORA results are much better. Our study is ongoing to evaluate the accuracy of this device.”

Dr. Wang adds that “theoretically, intraoperative measurements using the ORA system may improve the accuracy of IOL power prediction; the ELP (effective lens position) still needs to be estimated using this device.”

WaveTec reports that its own data from both Baylor cases and overall consistency showed a predictive error in the 0.41-0.42 D range using the ORA, with the most 15 recent Baylor cases showing a mean absolute error of 0.41 D. A recent ORA upgrade is demonstrating even better results in the number of patients whose outcomes showed less than a 0.50 D predictive error. The WaveTec data would put the ORA among the methods showing the lowest mean refractive error.

WaveTec believes post-refractive patients represent “a gateway application” for the ORA.

“We believe use of the ORA with these post-refractive patients is a gateway application for our technology,” WaveTec president and CEO Tom Frinzi says. “It is an application we have always had in mind.”

ONE SURGEON’S APPROACH

Problems with biometry

Cataract surgeons are now grappling with the issues presented by post-refractive cataract surgery

“It remains frustratingly difficult to obtain accurate keratometric biometry after a patient has had keratorefractive surgery of any kind,” says Michael Korenfeld, MD, ACOS, of Comprehensive Eye Care Ltd. in Washington, Mo. “Apparently, because of the differences in the corneal power induced by keratorefractive surgery, none of the existing corneal power measuring devices are sufficiently reliable to generate the same kind of reliability that they produce when thy are turned on a virgin cornea.”

Dr. Korenfeld approaches these patients by first obtaining corneal measurements from manual keratometry, computer-based Placido ring topography and an auto-keratometer.

“Then, I consult the records that describe the corneal power before the keratorefractive surgery,” he says. “Tell any of your patients who have had their keratorefractive surgery done elsewhere that they should obtain all of their records if possible, so the preoperative corneal measurements are not lost and the actual amount of treatment is known.”

Framing patient expectations

Dr. Korenfeld echoes the concern that patients who were willing to pay for keratorefractive surgery are also usually interested in a presbyopia-addressing implant and have higher expectations.

“It is very important to tell the patient that the accuracy of selecting an implant power that will produce a specific refractive outcome is less, as a result of having had the keratorefractive surgery,” he says. “I also tell them that the outcome of the first eye will help me to better select the implant for the second eye. It is always better to err slightly on the myopic side, if you have to be off target at all. If I use a Crystalens, I will send all of these data to the company consultant, and ask what they recommend.”

A POTENTIAL SOLUTION

Besides the ORA, one intriguing potential solution to this issue is a lens that can be adjusted once it’s been placed in the eye.

A lens that possesses this capability is the Calhoun Light-Adjustable Lens (Calhoun Vision, Pasadena, Calif.). Though still investigational in the United States, where it is about to enter a pivotal phase 3 trial, the Calhoun LAL is approved in Europe and Mexico and has had an extensive and positive trial in Canada.

In terms of effectiveness in post-refractive cataract surgery, Dr. Brierley in Victoria, B.C., was able to separate out 34 post-refractive eyes in 21 patients out of a 437-eye retrospective study of the Calhoun lens.¹ In the post-refractive eyes, adjustment began two weeks after the initial lens implantation, with patients receiving one, two or three adjustments to achieve target final manifest refraction spherical equivalent (MRSE).

In the final measurement, 74% of the eyes were within 0.25 D of target refraction and 97% of eyes were within 0.5 D. Mean absolute error at final measurement was 0.19 D, with 65% of the eyes achieving 20/20 vision.

Dr. Brierley noted in his study that the adjustability of the Calhoun lens provided him with the opportunity to correct for residual spherical and cylindrical error after stabilization of the postoperative refraction. He also found he could minimize or eliminate error caused by capsular bag contraction, surgical wound healing and pre-existing astigmatism. He concluded that “in patients with a history of laser refractive surgery, light-adjustable lens implantation and post-implantation adjustment provide a precise refractive outcome.” OM

“Cataract surgeons are now just beginning to grapple with the issues of post-LASIK and post-PRK surgery patients.”

REFERENCES

1. Brierley L. Refractive results after implantation of a light-adjustableintraocular lens in post-refractive-surgery cataract patients. Ophthalmology. 2013 May 21 (Epub before print).

2. Wang L, Douglas DD. Evaluation of new updates in IOL power calculations after LASIK/PRK. Invest Ophthalmol Vis Sci. 2013;54:ARVO E-Abstract 804.