Photorefractive keratectomy in the cat eye: Biological and optical outcomes
Accepted 12 February 2007.
Refers to erratum:
Erratum
Journal of Cataract & Refractive Surgery
August 2007 (Vol. 33, Issue 8, Page 1354) Full Text |
Full-Text PDF (66 KB)
Purpose
To quantify optical and biomechanical properties of the feline cornea before and after photorefractive keratectomy (PRK) and assess the relative contribution of different biological factors to refractive outcome.
Setting
Department of Ophthalmology, University of Rochester, Rochester, New York, USA.
Methods
Adult cats had 6.0 diopter (D) myopic or 4.0 D hyperopic PRK over 6.0 or 8.0 mm optical zones (OZ). Preoperative and postoperative wavefront aberrations were measured, as were intraocular pressure (IOP), corneal hysteresis, the corneal resistance factor, axial length, corneal thickness, and radii of curvature. Finally, postmortem immunohistochemistry for vimentin and α-smooth muscle actin was performed.
Results
Photorefractive keratectomy changed ocular defocus, increased higher-order aberrations, and induced myofibroblast differentiation in cats. However, the intended defocus corrections were only achieved with 8.0 mm OZs. Long-term flattening of the epithelial and stromal surfaces was noted after myopic, but not after hyperopic, PRK. The IOP was unaltered by PRK; however, corneal hysteresis and the corneal resistance factor decreased. Over the ensuing 6 months, ocular aberrations and the IOP remained stable, while central corneal thickness, corneal hysteresis, and the corneal resistance factor increased toward normal levels.
Conclusions
Cat corneas exhibited optical, histological, and biomechanical reactions to PRK that resembled those previously described in humans, especially when the OZ size was normalized to the total corneal area. However, cats exhibited significant stromal regeneration, causing a return to preoperative corneal thickness, corneal hysteresis and the corneal resistance factor without significant regression of optical changes induced by the surgery. Thus, the principal effects of laser refractive surgery on ocular wavefront aberrations can be achieved despite clear interspecies differences in corneal biology.
From the Department of Ophthalmology (Nagy, MacRae, Yoon, Wyble, Wang, Huxlin), University of Rochester, and Bausch & Lomb (Cox), Rochester, New York, USA
Corresponding author: Krystel Huxlin, PhD, Department of Ophthalmology, Box 314, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, New York 14642, USA.
Drs. MacRae and Yoon have served as consultants to Bausch & Lomb. Dr. Cox is a full-time employee of Bausch & Lomb. The University of Rochester has a research contract with Bausch & Lomb and has licensed intellectual property to them. No other author has a financial or proprietary interest in any material or product mentioned.
Supported by National Eye Institute grant RO1 EY015836-01, a grant from Bausch & Lomb Inc. to the University of Rochester's Center for Visual Science, grants from the University of Rochester's Center for Electronic Imaging Systems, a NYSTAR-designated Center for Advanced Technology, and by an unrestricted grant to the University of Rochester's Department of Ophthalmology from the Research to Prevent Blindness Foundation, New York, New York, USA.
Margaret Beha trained and tested the cats and did the feline ocular response analyzer (ORA) measurements. John Swanstone provided programming expertise. Tracy Bubel did the histological processing of the cat corneal tissue and hematoxylin staining. Emily Brandon, Shawn Kenner, and Sally Jensen analyzed the spot array patterns. Terry Schaeffer did the IOLMaster measurements. David Luce, PhD, provided access to the Reichert ORA. Gary Gagarinas assisted in laser refractive surgeries. Jens Bühren, MD, provided constructive discussions and feedback on the manuscript.
ABSTRACT