Effects of UVA+UVB solar radiation levels and cross-linking on animal model with Bowman’s layer: Chicken

Abstract

Purpose: Evaluate the corneal damage and wound healing in an animal model with Bowman’s layer after UVA+UVB radiation and epioff Cross-Linking (CXL). Methods: Adult Brown Classic chickens were randomly divided into three groups. The UVA+UVB group (20 eyes) was exposed to three doses of radiation (4.60 J/cm2) . The CXL group (12 eyes), was de-epithelialized and irradiated with UVA light (5.4 J/cm2) for 30 minutes. The contralateral eyes were used as a control (12 eyes). The animals have clinically follow-up, the epithelial closure was measured by fluorescein stain and corneal thickness by pachymetry. Keratocytes loss, subsequent cell repopulation, and healing events were analyzed after euthanasia at 24 hours, 15 and 30 days post-radiation on hematoxylin-eosin-stained sections. Cell death was detected by TUNEL assay, proliferation by BrdU (bromodeoxyuridine) immunofluorescence, and myofibroblasts differentiation by (αSMA) immunohistochemistry. Results: Re-epithelialization was at 5 ± 2.3 days in CXL and at day 2 ± 0.9 days in UVA+UVB. Pachymetry was higher after UVA+UVB than CXL (p<0.05). Cell death affected the whole thickness of stroma in the UVA+UVB group and anterior and middle stroma in CXL. At day 1, the UVA+UVB group showed a more significant reduction in the number of stromal cells. After 30 days, both groups showed a free band of cells below the epithelium. Conclusion: The damage and the healing response in chicken corneas after UVA+UVB and CXL demonstrated that Bowman’s layer has not been successful in protecting the cornea from radiation. Perhaps, other factors that are involved in corneal defense.