Purpose: To examine the effect of short-term 24-hr orthokeratology lens (OKL) wear on Pseudomonas aeruginosa binding, epithelial surface cell morphology, epithelial sheet thickness, and stromal thickness in a rabbit model.
Methods: Seventeen New Zealand white rabbits were treated according to the Association for Research in Vision and Ophthalmology Statement for the Use of Animals in Ophthalmic and Vision Research. Partial membranectomy was performed on all rabbits 1 week before the experiments. Baseline values for epithelial and stromal thickness and epithelial surface cell size were determined by in vivo confocal microscopy in one randomly chosen eye (n = 6). One week later, rabbits were fitted in the same eye with a hyper oxygen-transmissible OKL. Twenty-four hours later, confocal microscopy was repeated. The second group of rabbits (n = 6) was fitted with an OKL in one randomly chosen eye for 24 hr. P. aeruginosa binding to the corneal epithelium was assessed for the control corneas and those exposed to the test lens. Scanning electron microscopy was performed on a third group of rabbits to assess epithelial surface damage (n = 5).
Results: There was a statistically significant difference (P<0.001) in P. aeruginosa binding between the control (1.11 +/- 0.74 x 10(5) colony-forming units per cornea) and the OKL-wearing eyes (2.74 +/- 0.69 x 10(5) colony-forming units per cornea). The central epithelium thinned by 6.5% after lens wear (48.2 +/- 1.9 microm to 45 +/- 1.7 microm, P=0.005); however, central stromal thickness increased by 7.3% (322 +/- 22 microm to 345 +/- 29 microm, P=0.006). Compared with the baseline value, central epithelial cell size increased significantly from 1,253 +/- 140 mm(2) to 1,627 +/- 393 mm(2) (29.4%, P=0.02). Scanning electron microscopy showed increased surface epithelial damage associated with OKL wear.
Conclusions: This prospective, masked, pilot study showed that 24-hr hyper oxygen-transmissible OKL wear induced a statistically significant increase in P. aeruginosa binding to the epithelium of the rabbit cornea, accompanied by central epithelial thinning, stromal thickening, and surface cell damage assessed by scanning electron microscopy. Collectively, the data suggest that despite adequate lens oxygen transmissibility, the mechanical pressure inherent in the OKL design exerted on the corneal surface appears to be associated with increased adherence of P. aeruginosa to surface corneal epithelial cells, which may pose an increased risk for lens-related microbial keratitis, especially in overnight (i.e., closed-eye) wearing conditions. Future studies are needed to determine whether these results are similar in human wear and how P. aeruginosa binding during OKL wear compares with other lens-wearing modalities, such as daily or continuous soft lens wear.