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Transepithelial customized PRK safe and effective for re-treatment cases, surgeon says
The technique is more accurate, more stable than conventional PRK using manual epithelial removal.
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Pre-retreatment map of 33-year-old patient previously treated with PRK. | |
Differential map: achieved ablation profile. | |
Preoperative pachymetry map: central corneal thickness 539 µm; set ablation depth: 40 µm. | |
| Pachymetry map: postoperative central corneal thickness 502 µm; final ablation depth: 37 µm. Images: Mularoni A | |
NAPLES, Italy – Transepithelial customized PRK is a safe, effective and predictable re-treatment method, according to one surgeon.
The technique is a “no touch” modification of conventional PRK in which the epithelium is removed by laser rather than manually, said Alessandro Mularoni, MD, at Naples ‘04. The laser is set for a plano ablation to remove the epithelial thickness and then to perform customized refractive re-treatment, he said.
“When performing a second treatment, epithelial removal is often a problem and manual approaches might be inaccurate and traumatic,” Dr. Mularoni said.
He explained that the epithelium that grows over a previous refractive procedure is often irregular. Stromal irregularities might also be present between treated and nontreated areas, with a tendency toward hyperplasia in myopic eyes and hypoplasia in hyperopic eyes.
“The most common postoperative conditions that require re-treatment — regression and residual refractive error — can be caused by epithelial and stromal reactions to the treatment,” he said.
Although epithelial thickness and refraction are difficult to evaluate before a second treatment, laser removal of the epithelium with customized PRK is easier and more predictable than with manual PRK, Dr. Mularoni said.
When mapping the treatment, the CIPTA software of the LaserSight LSX 2000 takes into account the epithelial component in both the measurement of visual acuity and corneal shape, he said. This way he can predict the epithelial thickness after epithelial regeneration over the center of the optical zone and adjust the quantity and pattern of ablation accordingly, he explained.
“By creating a smooth, regular surface, we are fairly sure that the epithelium will be regrowing regularly, with a standard thickness of about 50 µm,” he said.
Predictable, stable results
Dr. Mularoni and colleagues performed transepithelial customized re-treatment in 47 eyes. The mean spherical equivalent before the first PRK treatment was –5.40 D. After PRK the patients had a mean residual refractive error of –2.01 D and a mean cylinder of –1.55 D. The mean follow-up was 12 months.
“Most patients required a second treatment for undercorrection. ... One [required a second treatment] for overcorrection. There were also cases of regression, decentration, central islands, haze and irregular astigmatism,” Dr. Mularoni said.
Using the CIPTA software, the LSX 2000 flying spot laser was set for a customized transepithelial ablation of 50 µm. A viscoelastic was used to protect the limbus over 360°, he said.
Follow-up exams were performed at 1, 3, 6 and 12 months. At each visit, uncorrected and best corrected visual acuity were measured, and biomicroscopy, corneal tomography and pachymetry were performed.
“UCVA improved from preoperative 20/60 to postoperative 20/30. Mean postoperative spherical equivalent was 0.25 D; mean cylinder was –0.56 D. Mean BCVA after transepithelial treatment not only improved preoperative re-treatment values, but was very near the mean BCVA of patients before the first PRK treatment. Results were stable over time,” Dr. Mularoni said.
He added that the treatment was safe since no patient lost visual acuity lines. Most patients maintained preoperative visual acuity and several gained up to six lines. Predictability was good, with 93.6% of the patients within ± 1 D of intended correction.
Complications were few; there were only two cases of overcorrection (greater than +0.50 D) and one case of regression, he said.
Advantages and limits
Transepithelial customized PRK re-treatment has several advantages, according to Dr. Mularoni.
“First of all, it is a ‘no touch’ technique, which minimizes trauma and leaves a smoother, more regular stromal surface. Re-epithelialization takes place more easily and consistently, preventing postoperative inflammation, regression and epithelial scarring,” he said.
“The laser software calculates the exact amount of epithelium that has to be removed, sparing corneal tissue and creating a smoother transition between the new optical zone and the untreated area,” he continued.
According to Dr. Mularoni, compared with conventional PRK, the treatment requires more cooperation on behalf of the patient because the laser is in use for a longer duration. It requires a confident approach to corneal topography by the surgeon since the software interacts with topographic data and results largely depend on the accuracy of these data, he said.
| LogMAR visual acuity ± 1 SD
Source: Mularoni A. |
For Your Information:
- Alessandro Mularoni, MD, can be reached at Ospedale Maggiore, Largo Negrisoli 2, 40133 Bologna, Italy; 39-051-6478608; fax: 39- 051-6478945; e-mail: alessandro.mularoni@ausl.bologna.it. Dr. Mularoni has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Naples ’04, the 9th Annual Joint Meeting of Ocular Surgery News, the Italian Association of Cataract and Refractive Surgery and the International Society of Refractive Surgeons, was held May 20-22. For information on future meetings, e-mail: meetingregistration@slackinc.com.
- OSN Correspondent Michela Cimberle is based in Asolo, Italy.