Laboratory evaluation of selective in situ refractive cornea collagen shrinkage with continuous wave infrared laser combined with transepithelial collagen cross-linking: a novel refractive procedure

BACKGROUND This research comprised a laboratory evaluation of a novel refractive surgery technique involving sequential corneal subsurface shrinkage-driven reshaping using a continuous wave mid-infrared laser application followed by stiffening via rapid transepithelial higher fluence collagen cross-linking for shape persistence/longevity on cadaver corneas. MATERIALS AND METHODS Ten cadaver corneas were used in this study. During use, all were affixed in an artificial chamber. Thermal delivery entailed a continuous wave laser at 2013 nm wavelength, approximately 650 mW power under scanner control (about 3 mm/sec linear draw speed), with a planoconcave sapphire applanation lens cooled to 8°C. Group 1 (n = 5, myopic treatment) eyes were exposed to three concentric annuli with diameters of 3 mm, 4 mm, and 5 mm. Group 2 (n = 5, hyperopic treatment) eyes were exposed to three concentric annuli with diameters of 6 mm, 7 mm, and 8 mm. The clinical change in shape of the cornea was visualized immediately under a slit-lamp. A transepithelial higher fluence corneal collagen cross-linking step followed each thermal treatment, comprising 0.1% riboflavin drops with 0.02% benzalkonium chloride and 0.2% carboxymethlycellulose in deuterated water (D(2)O) applied on the epithelium corneal surface for 10 minutes. Next, each cornea was exposed to 10 mW/cm(2) of ultraviolet A (365 nm) light for 10 minutes. The corneas were evaluated before and after thermal remodeling and cornea collagen cross-linking for corneal topography, corneal optical coherence tomography, cornea Scheimpflug tomography, and clinical photographs. RESULTS The histopathology effect was noted clinically as concentric white rings underneath the epithelium and Bowman's membrane, with the lesion depth extending down to 400 μm in the mid stroma of the cornea. This was confirmed by corneal anterior segment optical coherence tomography. The topographic change noted was a 4-8 diopter hyperopic shift in group 1 and a 2-6 diopter myopic shift in group 2. CONCLUSION This novel refractive surgery technique appears to generate a significant refractive change (+/-) in the cornea, without affecting the epithelium or Bowman's membrane and without any visible epithelial defect. The transepithelial collagen cross-linking used as a second step in the same procedure aims to stabilize this effect in the long term. Further clinical studies are planned to validate these initial clinical results.