193-nm excimer laser-induced fluorescence detection of fluoroquinolones in rabbit corneas

Objective: To measure the 193-nm excimer laser-induced fluorescence of fluoroquinolone-treated cadaver rabbit corneas. Methods: Prior to ablation with a commercially available ophthalmic excimer laser (Nidek EC-5000; Nidek Technologies, Pasadena, Calif), 35 cadaver rabbit corneas were treated with topical sterile balanced salt solution, 0.3% tobramycin sulfate, or the fluoroquinolones - 0.3% ofloxacin, 0.5% levofloxacin, 0.3% ciprofloxacin hydrochloride, or 0.3% gatifloxacin. The fluorescence generated from each ablated corneal layer was measured and used to identify the presence of antibiotic. This was achieved by training a partial least-squares model to discriminate between the fluorescence spectra of antibiotic-treated and antibiotic-free (healthy) cornea. Antibiotic concentrations down to 0.06 μg/mL were detected with high accuracy. Assuming a constant ablation rate of 0.3 μm per laser pulse, the number of corneal layers ablated to reach antibiotic-free cornea is used to calculate the penetration depth of the antibiotic. Results: The mean ± SD penetration to a detectable depth was as follows: 0.3% ofloxacin, 7.1±3.0 μ; 0.5% levofloxacin, 6.7±1.4 μm; 0.3% ciprofloxacin, 1.2±0.6 μm; and 0.3% gatifloxacin, 7.0±1.9 μm. The penetration depth of 0.3% tobramycin could not be determined because its fluorescence spectrum overlapped with that of the native cornea. Conclusions: Topical administration of fluoroquinolone-containing solutions results in measurable differences in laser-induced corneal fluorescence. Under these experimental conditions, 0.3% ofloxacin, 0.5% levofloxacin, and 0.3% gatifloxacin all appear to penetrate the epithelium significantly more than 0.3% ciprofloxacin (P<.02). Clinical Relevance: Monitoring of laser-induced fluorescence may be helpful in determining the penetration depths and concentrations of topically applied fluoroquinolones within the cornea.