Wavefront analysis: applications for refractive surgery, contacts, keratoconus

The past year has been a momentous one in the area of wavefront analysis, most notably marked by a significant step toward approval by the Food and Drug Administration. In August, the FDA’s ophthalmic devices panel unanimously recommended conditional approval of Alcon Surgical’s CustomCornea system for the correction of myopia up to 7 D and 0.5 D of astigmatism.

According to practitioners, this groundbreaking development is the next step in ushering wavefront technology into mainstream use.

“This is a landmark moment in the history of refractive surgery,” said Marguerite B. McDonald, MD, president of the American Society of Cataract and Refractive Surgery, clinical professor of ophthalmology at Tulane University in New Orleans and medical monitor for Alcon’s excimer laser trials. “We’ve had excellent results to date for the custom myopic eyes, and apparently the FDA ophthalmic advisory panel felt the same way.”

Scott MacRae, MD, professor of ophthalmology, of the Strong Vision Center in Rochester, N.Y., said scientists are learning more about wavefront analysis every year.

“We have learned that wavefront analysis is a much more powerful technology than we had anticipated even 2 years ago,” he said. “It has implications not only for laser refractive surgery, but for contact lenses, intraocular lenses and customized treatment for any kind of refractive error.”

Clinical findings

George Pettit MD, PhD, a chief scientist at Alcon, explained the workings of wavefront technology and Alcon’s CustomCornea to the FDA panel. He said the LADARVision system’s method of registration compensates for cyclotorsion and ensures an accurate match of the wavefront map and the ablation profile.

Dr. McDonald cited statistics from the presentation made to the FDA. She said that preoperatively there were two groups – the initial treatment group of 426 eyes that had 6 months of follow-up and a refined treatment group of 141 eyes that had a 1-month follow-up.

“The mean for the initial treatment group was –3.10 D, but with a range of up to –7 D. And the mean cylinder was –0.77 D with a range of up to –4 D,” she said. The refined treatment group had a mean of –2.65 D with a range of up to –5.50 D. The preoperative cylinder for the refined treatment group was –0.77 D, ranging up to –2.50 D.

“So you can see the initial treatment group was slightly more myopic than the second group,” she said. “But, in the initial group, 48% at 6 months were 20/16 or better uncorrected, 73% were 20/20 and 88% were 20/25.”

In the second group, where a refined algorithm was used, 63% were 20/16 at 1 month, 88% were 20/20 or better at 1 month and 98% were 20/25 or better.

With the initial group, 69% were ±0.5 D of intended correction within 6 months, and 94% were ±1 D. In the refined group, 90% were ±0.5 D at 1 month, and 99% were ±1 D.

According to Alcon, these results are expected to improve with adjustments to the nomogram.

Regarding the change in higher-order aberrations, Dr. McDonald said 38% of the patients showed a reduction in all higher-order aberrations, 44% had a reduction in coma and 46% showed a reduction in spherical aberrations.

In summary, Dr. McDonald said the study results demonstrated excellent visual acuity and more gain as well as less loss of mesopic contrast sensitivity.

“So, we are pleased,” she said. “We hope to go on to the non-virgin eyes, that is, the highly aberrated eyes that have had previous surgery, trauma or infection, and hyperopic eyes.”

Prominent aberrations

Although the significance of higher-order aberrations is becoming increasingly acknowledged, clinicians believe the correction of lower-order aberrations remains the top priority.

“Of course, lower-order aberrations are the biggest part of the visual problem in normal subjects — higher-order aberrations represent only about 17% of all visual problems,” Dr. McDonald said. “So if you correct the higher-order aberrations but are way off on lower-order aberrations such as sphere and cylinder, you haven’t accomplished much. The patient won’t notice that you’ve corrected the higher-order aberrations.”

Dr. MacRae said it has been determined over the past 2 years that patients with “virgin eyes” tend to have higher levels of coma and trefoil.

“And if they have refractive surgery, the more dominant higher-order aberration afterward is spherical aberration,” he said. “This tends to increase with the amount of myopia or hyperopia treated.”

Dr. MacRae cited David Williams’, PhD, recent studies at the University of Rochester in which it was found that some higher-order aberrations are more disabling than others.

The studies showed that higher-order aberrations that are in the center of the Zernicke pyramid — such as coma, secondary coma or secondary astigmatism — are more disabling than those higher-order aberrations that are in the periphery of the pyramid, such as pentafoil or quatrefoil.

“By better understanding wavefront, we are able to better diagnose and treat patients and understand their problems,” Dr. MacRae said. “We have also learned that patients have an increase in spherical aberration with conventional LASIK treatment, and that by using customized ablation and larger optical zones, we can further minimize or eliminate spherical aberration increases.”

Applications of wavefront

With the possibilities of wavefront technology expanding at an astounding rate, practitioners are now assessing which uses of wavefront will prove to be most beneficial.

“Every doctor wants to address unhappy patients first,” Dr. McDonald said. “The true goal for the doctors is to take care of the patients who are unhappy from suboptimal surgery in the past.”

Among these surgeries are early PRK, early LASIK, decentered ablations, bad flaps, corneal scars from trauma and infection, corneal transplant patients who are unable to wear contact lenses, former RK patients and former AK patients. Also included in this category would be previous hexagonal keratotomy patients or those who have had cataract surgery and are left with irregular astigmatism.

According to Raymond Applegate, OD, PhD, director of the Visual Optics Institute at the University of Houston, measuring the eyes’ optical aberrations with wavefront is moving the refractive surgery industry toward better outcomes.

“We can now measure the aberrations that have been introduced by older types of refractive surgery and know that we weren’t doing a very good job,” he said.

Dr. Applegate further believes that wavefront measurement will be very useful in preventing the introduction of new aberrations. “Now that we know how to measure ocular aberrations, it gives us the necessary information to try to minimize them,” Dr. Applegate said.

Ian Cox, PhD, professor and research collaborator at the Center for Visual Sciences, University of Rochester, agreed that an increased understanding of higher-order aberrations will enable improved correction of them.

“With conventional refractive surgery, we do correct their defocus and astigmatism,” he said. “But during the past few years, it has become clear that the surgical procedure itself actually introduces higher-order aberrations such as spherical aberration and possibly coma. With wavefront, you can not only see them, but detect subtle changes and understand when they are actually affecting the patient’s vision.”

Wavefront and keratoconus

Another useful application of wavefront technology is in identifying and treating keratoconic patients, Dr. Cox said.

“Even though these patients may have been showing 20/20 Snellen acuity, they would still report to the practitioner that their vision was not that crisp,” he said. “And especially at night, their vision might not be as good.”

Wavefront sensors allow the practitioner to actually measure a keratoconic patient with vision correction in place, Dr. Cox said.

“It helps you understand the quality of the retinal image the patient is getting,” he said. “And that can actually help a practitioner adjust the fit on a keratoconic patient to improve the quality of vision. It can also be used to identify a keratoconic suspect.”

Dr. Cox said wavefront could mean a new development in the area of keratoconus detection. “Interestingly, for a number of years, we either thought of somebody as having keratoconus or not. Then, with the advent of corneal topography, we started recognizing the beginning of keratoconus by topography.”

The wavefront sensor now allows the practitioner to look at the retinal image quality, which can be very useful in combination with topography.

“One of the first signs of clinical keratoconus is an increase in the amount of coma above what we see in the normal population,” Dr. Cox said. “This is caused by the apex of the cornea moving away from the line of sight. Now, you can identify when patients are starting to experience visual disturbances based on the corneal changes. In combination with the topography, it helps detect these patients earlier and manage them better.”

Improved contact lenses

One of the most exciting new applications of wavefront technology is in the area of contact lenses, which are now being customized using wavefront analysis.

Polyvue Technologies recently began fitting some of the first soft lenses with a wavefront corrective pattern. Dr. McDonald worked with the company on these fittings, which were done in August.

Dr. McDonald said although the fittings were done in August, the patients were told the lenses would not be delivered until October. “Because this is the first batch, we want to take our time with it,” she said.

Dr. McDonald said she believes there will be three target markets for wavefront-guided contact lenses. “The first will be people with highly aberrated eyes who had bad RK or LASIK and never want surgery again, but who still can’t see very well,” she said. “These are soft lenses, so almost anybody will be able to wear them. So some patients who have had bad experiences with surgery will wear these lenses forever.”

A second group will want to “kick the tires” of wavefront to determine whether they might opt for wavefront-based refractive surgery in the future, Dr. McDonald said.

A third group would comprise individuals with no desire to try refractive surgery, Dr. McDonald said. “Some people would never consider refractive surgery, but would like to have one or two lines of improvement in their best-corrected vision or better night vision,” she said. “These are people who are very happy contact lens wearers, but may want to improve their golf score or feel safer driving at night.”

For Your Information:

• Marguerite B. McDonald, MD, is the director of the Southern Vision Institute in New Orleans and a clinical professor of ophthalmology at Tulane University. She can be reached at 2820 Napoleon Avenue, Suite 750, New Orleans, LA 70115; (504) 896-1250; fax: (504) 896-1251. Dr. McDonald has no direct financial interest in the products mentioned in this article. She is a paid consultant for Alcon and PolyVue.
• Scott MacRae, MD, is a professor of cornea and refractive surgery at Strong Vision Refractive Center at the University of Rochester. He can be reached at Strong Vision Refractive Center, 100 Meridian Centre, Rochester, NY 14618; (585) 273-2020; fax: (585) 756-1975. Dr. MacRae has no direct financial interest in any of the products mentioned in this article. He is a paid consultant for Bausch & Lomb.
• Raymond Applegate, OD, PhD, is director of the Visual Optics Institute at the University of Houston. He can be reached at 505 J.D. Armistead Building, Houston, TX 77204-2020; (713) 743-2020; fax: (713) 743-2053. Primary Care Optometry News could not determine if Dr. Applegate has any financial interest in any of the products mentioned in this article, or if he is a paid consultant for any of the companies mentioned.
• Ian Cox, PhD, is an adjunct professor and research collaborator at the Center for Visual Science, University of Rochester, Rochester, NY 14627-0270; (585) 275-2459; fax: (585) 338-0441. Dr. Cox has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any of the companies mentioned. He is a research fellow of Bausch & Lomb.