Evaluation of irradiated corneas using scatterometry and light and electron microscopy

OBJECTIVE:: To determine if sterilization of donor corneas by irradiation alters optical, histologic, or ultrastructural tissue characteristics. METHODS:: Blinded assessment of 10 irradiated and 10 nonirradiated donor corneas by a scatterometer used to objectively measure backscattered corneal light. Light and electron microscopy were performed on samples from both groups. RESULTS:: The mean scattering of the nonirradiated (control) corneas was significantly lower (0.0060 ± 0.0034, mean ± SD) than the scattering of the irradiated corneas (0.023 ± 0.0078; P = 0.0001). There was no statistical difference between ages, days in storage, or central corneal thickness of the 2 groups. Light microscopic evaluation revealed attenuation of the irradiated corneal epithelium with superficial stromal clefting. Transmission electron microscopy demonstrated similar fibril diameter in the nonirradiated and irradiated corneas. Although the mean interfibrillar distance was similar between the nonirradiated and irradiated groups, the interfibrillar distance in the superficial stroma was increased in the nonirradiated compared with the irradiated groups (15.4 ± 2.4 vs. 11.8 ± 0.98 nm; P ≤ 0.05). CONCLUSIONS:: Our data quantitatively support increased light scatter after irradiation, which cannot be attributed to increased corneal thickness. Irradiation alters the histology of the epithelium and the ultrastructure of the superficial corneal stroma. Increased light scatter because of epithelial changes would not be expected to impact postoperative visual function. However, increased light scatter because of stromal changes may affect postoperative visual function if used for optical corneal rehabilitation. Further investigation is warranted to determine whether attenuated epithelium or superficial stromal changes are the cause of increased light scatter in the irradiated corneal tissue.