Abstract
Purpose: :
The purpose of this study was to investigate the effects of concomitant dry eye and corneal alkali burn using a murine model.
Methods: :
C57BL/6 mice were divided in 2 groups: alkali injury (AI) or AI+ desiccating stress (AI+DS). Unilateral corneal alkali injury was created on a left eye of C57BL/6 mice, by placing a of 1N NaOH soaked 2.0mm diameter filter paper disc on the cornea for 10 seconds, followed by rinsing with balanced salt solution. Desiccating stress (DS) was induced by subcutaneous injection of scopolamine and exposure to a drafty low humidity environment for 5 days (DS5). The contralateral eyes served as controls: untreated (UT, no alkali injury, no dry eye), and DS5 (desiccating stress for 5 days). Mice were euthanized after 5 days and eyes and adnexae were collected for histology. Corneal frozen sections were immunostained for matrix-metalloproteinase 9 (MMP-9) and fluorescence intensity measured in the epithelium and in the stroma using NIS Elements Software.
Results: :
All eyes subjected to alkali burn and concomitant desiccating stress showed corneal perforation, and diffuse opacification of the surrounding cornea stroma 5 days post-injury. Eyes subjected to AI alone had different degrees of corneal opacification, but no corneal perforation. UT and DS5 eyes had no visible corneal opacification, nor perforation. Histologically, the corneas subjected to AI showed detached corneal epithelium, and moderate inflammatory cells in the corneal stroma. However, eyes subjected to AI+DS had central perforation and collapse of the anterior chamber, with iris and lens attached to the posterior cornea. This was accompanied by total loss of corneal epithelium and massive infiltration of corneal stroma by inflammatory cells that dissected tunnels in the cornea from the periphery. Immunostaining for MMP-9 showed that either DS alone or AI alone induced significant MMP-9 immunoreactivity in corneal epithelium (P=0.001 and P=0.006 vs. UT, respectively). The combination o f AI+DS induced a significant increase in MMP-9 reactivity in corneal stroma, to levels similar to the ones observed in the epithelium of DS or AI alone groups.
Conclusions: :
concomitant desiccating stress and alkali injury increased inflammatory cell infiltration and MMP-9 production in the cornea, leading to corneal perforation.
Keywords: cornea: tears/tear film/dry eye • inflammation • cornea: epithelium