Issue: June 10, 2016
June 03, 2016
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PRK with cross-linking improves visual acuity in eyes with keratoconus

Issue: June 10, 2016
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Topography-guided PRK followed by corneal collagen cross-linking yielded a greater improvement in visual acuity than cross-linking alone in eyes with progressive keratoconus, a study found.

“In our opinion, the most significant finding from this study was that with cautious implementation of topography-guided surface ablation, patients with keratoconus can be significantly benefited without compromising the stabilization effect of CXL,” Georgios A. Kontadakis, MD, the corresponding author, told Ocular Surgery News. “While planning this procedure and performing it, it is crucial to address safety precautions at all times. The other original finding of our study was the more potent effect of the combined procedure in comparison to CXL alone, as seen in confocal microscopy. The biomechanical consequence remains to be clarified, even though clinically it was similar in both our groups.”

The combined procedure is designed to regularize and stabilize the corneal surface, Kontadakis said.

“With PRK we try to regularize the corneal surface and improve patients’ vision, which is a known effect from previous studies on forme fruste keratoconus, and with CXL we address the stability issue. [The target] of the procedure is not full refractive correction but visual improvement and halting of progression,” he said.

The prospective study, published in Ophthalmology, included 60 eyes of 48 patients with progressive keratoconus.

Thirty eyes underwent topography-guided PRK followed by cross-linking, and 30 eyes underwent cross-linking alone. Mean follow-up was 39 months.

Depth of cross-linking treatment in confocal microscopy was 269.8 µm in the cross-linking alone group and 299.7 µm in the combined group; the difference was statistically significant (P < .001).

“The main safety consideration is always the stromal thickness. We always want to leave a sufficient stromal bed thickness for the subsequent CXL procedure to be done with safety for the endothelium, and we never want to pass the limit of 50 µm maximum ablation depth. A refractive overcorrection is anticipated, and this is also taken into account,” Kontadakis said.

At final follow-up, mean uncorrected distance visual acuity improved 9.1 letters in the cross-linking only group and 26.9 letters in the combined group; the between-group difference was statistically significant (P = .004).

Mean corrected distance visual acuity improved 4.7 letters in the cross-linking only group and 8.6 letters in the combined group (P = .034).

“We believe that it is beneficial for the patients to treat not only the sphere and cylinder but also the corneal irregularity in order to improve their visual performance and help them be more independent from contact lenses,” Kontadakis said.

Sixty-three percent of patients in the combined treatment group and 27% in the cross-linking only group gained two or more lines of corrected distance visual acuity; the difference was statistically significant (P = .009).

The difference between preoperative and postoperative spherical equivalent refraction was significant in the combined treatment group (P < .0001) but not in the cross-linking only group.

The difference between preoperative and postoperative defocus equivalent refraction was significant in the combined treatment group (P < .0001) but not in the cross-linking only group.

At final follow-up, both steep and flat keratometry readings were significantly flatter in the combined treatment group than in the cross-linking only group. – by Matt Hasson

Disclosure: Kontadakis reports no relevant financial disclosures.