Refractive procedures continue to be refined by trends

December 1, 2008
Lynda Charters

Collagen cross-linking, the newest advancement in the refractive arena, possibly will stabilize keratoconic and ectatic corneas. LASIK, an area that always is improving, has seen changes in flap sizes and lasers. Knowledge of corneal biomechanics also is progressing to provide more information than ever before with new instrumentation. The phakic IOL market has expanded considerably, catering to those with high myopia. IOL options for pseudophakia also are expanding, and refractive lens exchange remains popular for hyperopia. In addition, questions of patient satisfaction postLASIK are being answered by an FDA task force.

Key Points

The refractive arena includes several notable established and up-and-coming technologies that have captured the attention of ophthalmologists during 2008.

"The spectrum of refractive surgery is now widely considered to encompass both corneal as well as lenticular surgery, including cataract surgery," said Uday Devgan, MD, in private practice at the Maloney Vision Institute, chief of ophthalmology at Olive View University of California Los Angeles (UCLA) Medical Center, and associate clinical professor at UCLA School of Medicine, Los Angeles. "By offering a full spectrum of procedures, refractive surgeons can treat a wider range of refractive errors among a broader age range of patients."

"[Collagen cross-linking] is a new and exciting technology that will possibly stabilize keratoconic and ectatic corneas," said Peter Hersh, MD. This technology, which emerged from the work of Theo Seiler, MD, and Michael Mrochen, PhD, uses ultraviolet (UV) light and riboflavin, the combination of which causes the collagen of the cornea to form covalent bonds with the goal of stiffening the cornea to treat keratoconus and corneal ectasia. "The primary goal is to make the weak ectatic corneas stronger in order to prevent progression of the keratoconus and the ectasia," he said.

In Europe, Dr. Hersh said, the studies are suggesting that the process is succeeding in enhancing corneal stability. In addition, investigators have seen slight flattening of the cornea as the cross-linking process works over time.

In the United States, a multicenter FDA study of collagen cross-linking, led by medical monitor Doyle Stulting, MD, of Emory University, began in January 2008. Two groups of patients are being treated, those with progressive keratoconus and those with progressive corneal ectasia following LASIK. The study calls for the recruitment of 160 patients for the treatment group and for a control group that receives only riboflavin drops every 2 minutes for two sessions of 30 minutes each. The treatment group undergoes the conventional epithelial debridement, application of riboflavin drops for 30 minutes, and treatment with UV light for 30 minutes, after which a contact lens is placed.

This technology is causing a great deal of excitement as evidenced by the fourth International Congress of Corneal Crosslinking taking place this month in Dresden, Germany.

Dr. Hersh personally has treated about 60 patients with corneal collagen cross-linking, and he and his colleagues are beginning to gather 3- and 6-month follow-up data.

"This is a promising technology," Dr. Hersh said. "We hope to help stabilize keratoconic and ectatic corneas. If the procedure is found to be safe and effective, collagen cross-linking may be of great help in these challenging cases."

LASIK flaps/SBK/PRK

Corneal refractive surgeons have been seeing a shift toward the creation of thinner LASIK flaps, often made with femtosecond lasers. As the corneal flaps become thinner and closer to Bowman's membrane, surgeons are referring to the new procedure as SBK, Dr. Devgan said.

"The rationale is that thinner LASIK flaps created with femtosecond lasers, often with smaller diameters, can provide the comfort and fast recovery associated with LASIK while offering a lower risk of future ectasia that PRK is purported to carry," he said. "An increasingly larger percentage of LASIK cases are being performed with femtosecond lasers, and the consumer awareness of this technology is increasing."

Miguel Maldonado, MD, also pointed to the increasing interest in SBK as well as pharmacologically modulated PRK.

"For those who have a femtosecond laser available to them, SBK will be the procedure of choice and pharmacologically modulated PRK for surgeons who do not. For those candidates who participate in contact sports and those who are at risk of ocular trauma because of their careers-such as police officers, military personnel, and firemen-advanced surface ablations will always be slightly superior," said Dr. Maldonado, chief of the Refractive Surgery Unit, University Clinic of Navarra, Pamplona, Spain, and associate professor at the University of Valladolid School of Medicine, Valladolid, Spain. "Based on our experience, with any trauma to the ocular surface after a surface procedure the eye responds as if it had not undergone a surgical procedure, whereas when there is a flap interface created by either a microkeratome or a femtosecond laser there is a tendency for flap dislocation, post-traumatic diffuse lamellar keratitis, or both."

In Spain, Dr. Maldonado reported, advanced surface procedures with modern excimer lasers create smooth ablation surfaces, as opposed to the systems used in the 1990s, and the use of chilled solutions with appropriate pharmacologic modulation does not induce visually relevant corneal haze beyond 6 months postoperatively.

"I have only seen anecdotal cases, that is, fewer than one in 500 patients, with significant corneal haze," he said. "This haze is related more to uneven eye drop administration, even in those corrections of myopia over 5 D."

He said he does not advise the prophylactic use of mitomycin C (MMC) currently because "no one really knows the long-term outcome of a drug that binds covalently to the therapeutic target. I simply believe that there is no role for MMC in primary procedures nowadays. It would have been a good adjunct in the 1990s, however."

Dr. Hersh also said more surgeons in the United States are shifting to surface refractive procedures with adjunctive MMC and the newer generations of lasers.

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