By Jason E. Stahl, MD
Photoactivated riboflavin may hold promise as a one-time treatment for superficial corneal infections, primarily those that are bacterial, according to the early results of this first prospective U.S. study to evaluate photoactivated riboflavin for infectious keratitis.
The authors say that since ultraviolet light can activate herpetic infections, cross-linking should be avoided in patients with history or suspicion of the virus, but otherwise it posed no obvious safety risk in this study and appeared to be most effective when the infection depth was limited. They conclude that cross-linking may be a helpful adjunct in problematic cases with antibiotic resistant organisms, patient compliance issues or variable drug absorption into the cornea.
They report results for the first 40 patients of a larger case series of infectious keratitis treated by instilling riboflavin 0.1% solution for 30 minutes to saturate the cornea, followed by exposure to 365-nm ultraviolet-A (UVA) light (3 mW/cm2) for 15 to 45 minutes, with continued instillation of riboflavin. Standard topical antibiotic treatment was continued.
The authors hope to include more than 200 patients in the study in order to achieve the statistical power needed to investigate efficacy on different organisms and with different durations of cross-linking (30 vs. 45 minutes). The initial patients represent advanced infections that had responded poorly to conventional treatment or had been treated ineffectively before enrollment at a tertiary care center.
Seven eyes (18 percent) had a previous keratoplasty. Bacterial species were identified in 24 eyes, fungal in seven, protozoan in two, viral in one, and no organism in six. The maximum infiltrate diameter ranged from one to 12 mm. The epithelial defect diameter was zero to 8 mm before treatment.
In six cases (two bacterial, three fungal and one without growth), keratitis did not resolve successfully and the eye received a penetrating keratoplasty (PK). In one eye with prior PK, the infection resolved following treatment, but a regraft was required to address perforation of the PK incision.
The therapy appeared most successful in bacterial infections less than 250 microns deep. It was less effective in fungal infections, although the number of cases was too low to make any significant conclusions. One patient with negative cultures became worse with treatment and subsequently developed dendrites.
Based on these early findings, the authors recommend a randomized study evaluating CXL with and without antibiotics for corneal infections less than 250 μm deep.