Refractive outcomes of PRK for mild to moderate myopia remain stable up to 12 years after surgery, according to a long-term British study.
Madhavan S. Rajan, MRCOphth, FRCS, and colleagues at St. Thomas’ Hospital in London reported on 68 patients 12 years after they participated in the first U.K. excimer laser clinical trial for the treatment of myopia with PRK. According to the researchers, this is the first report on patients evaluated more than 10 years after the procedure.
The results are promising in that the eyes showed refractive stability and few complications, including regression, the researchers said. Some regression occurred in the first year after the procedure, but there was no significant change in the mean spherical equivalent refraction after 1, 6 and 12 years postoperatively, the authors said. Best corrected visual acuity and uncorrected visual acuity improved, while complications such as corneal haze resolved with time. Corneal haze symptoms resolved mostly within 1 year, they said.
Researchers found that 75% of patients who underwent 2-D corrections and 65% of those who underwent 3-D corrections were within 1 D of intended correction at 12 years. Four percent had residual corneal haze, and 12% had persistent nighttime halos at 12 years. Researchers attributed the halos to the small size of the ablation zone. Dry eye occurred in 3% of patients. No eyes developed corneal ectasia, they said.
“This study highlights the importance of ablation zone size in improving night vision problems and refractive predictability after PRK,” Dr. Rajan said in a press release from the American Academy of Ophthalmology. “Given that PRK has proven long-term stability, newer developments such as wavefront-guided customized ablations at the corneal surface are likely to yield better results than LASIK, while preserving the biomechanical integrity of the cornea.”
PRK concerns abated
Previous short-term studies of PRK yielded concerns about the long-term stability of the procedure, Dr. Rajan and colleagues said. Because regression, haze and hyperopic shift occurred in the short term after the procedure, many researchers were concerned the complications would worsen with time. This study showed that complications of PRK are more common in the short-term as opposed to the long-term, the researchers said.
“The present study has shown that the postoperative refraction continues to be stable for up to 12 years. More importantly, there was no significant evidence of late regression or progressive hyperopic shift,” the authors said. “These observations infer that chronic stromal remodeling and corneal ectasia are unlikely events in PRK.”
In many cases, findings observed at the 6-year evaluation remained unchanged at the 12-year mark. Overall, regression, corneal haze and aberrations were minimal, the researchers said.
Most patients underwent bilateral PRK. Fifty-one percent of these patients said they were satisfied with their results, 15% were dissatisfied, and 12% had night-vision problems, the researchers said.
Eighteen patients underwent unilateral PRK. Seven of these patients had monovision, wore no glasses and had VA of 20/32 or better in the operated eye. Patients with successful monovision had less than 2-D of anisometropia between the eyes, they said.
At 12 years, 64 eyes (94%) had BCVA improved from preoperative levels, the researchers said. Eight eyes (11%) gained one Snellen line and three (4%) gained two lines. One eye (1.4%) lost two lines, and three eyes (4%) lost one line, they said. Sixty-six percent of patients wore glasses even though full refractive correction was achieved. Patients that lost lines lost no more between the 6- and 12-year evaluations, the study found.
Researchers recommended informing patients of the possibility for myopic regression. Minor regression was noted in six patients who underwent unilateral PRK. Most of the regression, however, occurred soon after the procedure and stabilized with time, they found.
“The regression curve was biphasic, with a much steeper slope within the first postoperative year. It can be seen that the magnitude of regression was related to the height of the hyperopic shift, which in turn correlated with the value of attempted myopic correction,” the researchers said.
They also observed minimal refractive change, which could be attributed to aging, the researchers said.
“All patients showed a marked change in the dioptric value between the central 4-mm ablation zone and the peripheral unablated cornea,” they said.
Although the researchers saw no change in astigmatism, they noted some asymmetry in ablated zones.
Corneal haze resolved
As with regression, complications such as corneal haze and night vision halos, which were problematic in the early years, abated with time. Researchers noted that corneal haze peaked between 3 and 6 months and mainly resolved within the first year after the procedure.
At the 12-year follow-up, 64 eyes had clear corneas; none had worsening haze or late development of haze, the researchers said. They observed that patients with higher myopic correction had more problems with halos than patients with less than 4 D of correction.
Most patients were satisfied with their vision in general, the researchers said. Eight patients who reported halos at night at the 6-year follow-up said the symptoms had subsided by the 12-year evaluation, the researchers said. Mean scotopic pupil size was 6.6 ± 0.35 mm (range: 6 mm to 7 mm).
Although LASIK still dominates the market for refractive procedures, the 12-year data is reassuring for surgeons following patients who have had PRK, the researchers concluded. In addition, whereas some LASIK studies have shown that vision is compromised in the long term, this study did not reflect that finding for PRK, the authors said. Instead, BCVA improved with time. In a separate study, the authors said, they will disclose additional findings of the long-term follow-up of patients who underwent PRK with 5-mm and 6-mm ablation zones.
For Your Information:
- Madhavan S. Rajan, MRCOphth, FRCS, can be reached at Flat 2, 14 Park Hall Road, London SE21 8DW, United Kingdom; e-mail: email@example.com.
- Rajan MS, Jaycock P, et al. A long-term study of photorefractive keratectomy. Ophthalmology. 2004;111:1813-1824.
- Jeanne Michelle Gonzalez is an OSN Staff Writer who covers all aspects of ophthalmology, specializing in practice management, regulatory and legislative issues. She focuses geographically on Latin America.