Stromal response to orthokeratology: an X‐ray diffraction study

Abstract

Abstract Purpose: To examine the impact of overnight orthokeratology lens wear on stromal collagen fibril diameter and spacing using synchrotron X‐ray diffraction. Methods: Seven New Zealand White rabbits (10 eyes) wore orthokeratology lenses (Capricornia, Brisbane, Australia) overnight during a 2‐week period to determine the effect of corneal refractive therapy on stromal collagen fibrils. To verify the effectivity of treatment, corneal topography (Medmont, Brisbane, Australia), corneal thickness (Allergan Humphrey pachymetry) and refractive error (retinoscopy) were measured prior to and every 3‐4 days during the treatment period. Following completion of treatment, rabbits were euthanased and corneas immediately dissected and snap frozen for subsequent X‐ray diffraction analysis every 1mm over the central c.10mm horizontal corneal band. Results: Orthokeratology treatment induced an average change in refraction of 2.0 +/‐ 1.3DS, and a topography‐measured treatment zone diameter of 4.2 +/‐ 0.7mm. The results from X‐ray diffraction revealed no significant difference in collagen fibril diameter between treated and untreated eyes (p>0.05). Interfibrillar spacing (IFS) was positively correlated with tissue hydration but no significant association between the change in IFS and refraction was apparent. Conclusions: The magnitude and time course of refractive change induced by orthokeratology in the rabbit eye is similar to that reported in humans, producing significant rapid and characteristic changes in corneal topography. Such specific changes in topography seem limited to the epithelial layers, with no parallel topographic modification evident in the underlying stromal architecture.