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Early results suggest combined cross-linking and PRK can improve vision quality in early keratoconus
By Linda Roach, Contributing Writer
Simultaneously treating certain cases of early keratoconus with corneal cross-linking and custom photorefractive keratectomy (PRK) ablation of less than 50 microns is a safe and effective way to improve visual quality in young adults while halting progression, a Saudi Arabian study has concluded.
Even though keratoconus patients still have good BSCVA, their visual quality improves because the combined treatment reduces visual distortions caused by their misshapen corneas, said the study's author, Waleed Al-Tuwairqi, MD, of the Elite Surgery Center in Riyadh, Saudi Arabia.
Dr. Al-Tuwairqi reported one-year follow-up data from 15 patients (22 eyes) at the American Academy of Ophthalmology's Annual Meeting in Chicago in October 2010.
He said the study's results are important for corneal surgeons in countries in and around the Middle East, because their patient population is getting younger.
Strict criteria recommended
Dr. Al-Tuwairqi emphasized that his study showed that the combined procedure should be done only in a subset of patients with early keratoconus. He recommended that candidates meet strict inclusion criteria:
- central corneal thickness no less than 450um,
- ablation depth no greater than 50um,
- K reading of no greater than 50.0 (in diopters),
- spherical equivalent correctable by 50 ?m of ablation,
- topographic picture of early keratoconus or keratoconus suspect and BCVA of at least 20/25.
In an interview, Dr. Al-Tuwairqi said he undertook the study because young adults with early keratoconus often complain about their continuing poor visual quality after cross-linking with UV-A and riboflavin. Such patients have been considered inappropriate candidates for PRK, because they still can achieve good BSCVA.
Visual function is the goal
"When I first began using cross-linking, I noticed that it might stop the progression of the disease but it does not do anything with visual function," Dr. Al-Tuwairqi said. "If the management plan does not address both issues, it is incomplete."
The 15 patients in Dr. Al-Tuwairqi's initial study were between 19 and 40 years of age, with a mean age of 25. (He has since performed more combined procedures, bringing the total number of patients to approximately 100.)
The eyes in the study were required to have early keratoconus with evidence of progression, a transparent cornea without scarring and good visual acuity with spectacles. Topographically, eight of the 22 eyes had inferior steepening. The remaining eyes fell into the following four categories: asymmetric bowtie, pellucid marginal degeneration, symmetric bowtie and asymmetric bowtie with skew deviation.
Identifying risk factors
After analyzing at least one year of follow-up data for each eye, Dr. Al-Tuwairqi concluded that the eyes that did worse after surgery had thinner corneas (either before or after surgery), preoperative BCVA worse than 20/25, K readings closer to 50 (in diopters) and larger refractive errors.
Dr. Al-Tuwairqi used custom PRK profiles from two models of excimer laser: Visx and Schwind. The refractive target was emmetropia.
In 21 of 22 study eyes, post-op UCVA results were excellent, at 20/22.5 or better. Topography, K-readings and astigmatism also improved. Among the 21 eyes, UCVA was the same as the pre-op BSCVA in 45 percent, and one or more lines better in 50 percent, he said. With refractive correction, post-op acuity ranged from 20/28.5 to 20/16 for all 22 eyes.
Deeper ablations appear problematic
Although the study was not large enough to reach statistical significance, the results in the eye with the worst BCVA after surgery (20/28.5), eye 22, suggest that deeper PRK ablations should be avoided, Dr. Al-Tuwairqi said. That eye had a larger refractive correction than the other eyes and subsequently developed vision-impairing haze, ultimately losing two lines of UCVA compared to pre-op.
A new patient population
When the only surgical solution for keratoconus was corneal transplant, patients delayed surgery until very late.
Today, patients are likely to be in their 20s and 30s, with early-stage keratoconus. They want to preserve as much of their vision as possible, and they are disappointed about their vision results after cross-linking, Dr. Al-Tuwairqi said.
For certain patients, combined corneal cross-linking and PRK might be the answer, even though its direct effect on the eye's refractive power is minimal.
"If the disease is early, in most of the cases there is not much change in refraction from the PRK," he said. "Early cross-linking also does not alter the refraction much."
Reduced aberration is key
The combined procedure reshapes the cornea, reducing higher-order aberrations, Dr. Al-Tuwairqi said. Indeed, satisfaction is high among the approximately 100 patients he has treated in this manner.
After surgery, 91 percent (20) of the patients could read signs, drive at night and read the news bar at the bottom of the TV screen. The other 9 percent (2) could function that well most of the time, but some tasks requiring very sharp vision were difficult.
Dr. Al-Tuwairqi has begun teaching his combined corneal cross-linking and PRK technique to other surgeons in the region, and some have begun offering it to young adults who meet his recommended inclusion criteria.
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Dr. Kanellopoulos is a consultant for Alcon, Inc., maker of the Wavelight excimer laser that he uses for topography-guided photorefractive keratectomy.