Modulation of matrix stiffness throughout corneal wound healing following phototherapeutic keratectomy

Abstract

Purpose: While many attributes of corneal stromal wound healing have been well characterized, the alterations in the biophysical attributes of the corneal wound itself have not been adequately investigated. Corneal stromal haze is a relatively common complication following phototherapeutic keratectomy (PTK) and compromises corneal transparency and visual acuity. We hypothesized that the elastic modulus, a measure of stiffness, would increase following PTK and correlate with the appearance of stromal haze. The purpose of this study was to determine the elastic modulus of the corneal stroma following PTK in rabbits using atomic force microscopy (AFM).

Methods: Following corneal epithelial debridement, New Zealand white rabbits underwent PTK (6 mm diameter, 100 μm deep) on the right eye (OD). Corneal wound healing was monitored with digital slit lamp biomicroscopy, ultrasonic pachymetry and spectral-domain optical coherence tomography (SD-OCT). Rabbits were euthanized at days 1, 3, 7, and 21. Immediately following euthanasia, the corneal epithelium was removed from both eyes (OU) and the left eye (OS) received a PTK similar to OD. An 8 mm central corneal button was harvested OU and AFM was performed.

Results: Mean ± SD elastic modulus of the anterior corneal stroma OS was 0.62 ± 0.29 kPa. At days 1 and 3, elastic modulus was 2.5-fold greater OD versus OS and correlated with an increase in central corneal thickness from corneal edema. At day 7, elastic modulus was 8-fold greater OD in comparison to OS and correlated with the appearance of stromal haze as well as corneal re-epithelialization. At day 21, stromal haze increased in density with elastic modulus remaining 8-fold greater OD versus OS.

Conclusions: Elastic modulus of the anterior corneal stroma is dramatically altered following PTK and correlates initially with the development of edema and later with formation of stromal haze. With emerging engineering approaches for modulating corneal biomechanics such as crosslinking with riboflavin and hyaluronidase to stiffen or soften the stroma, respectively, it is imperative to better understand the long-term consequences of changing the biophysical characteristics of the corneal stroma.

Keywords: 484 cornea: stroma and keratocytes • 686 refractive surgery: PRK • 765 wound healing