Specular microscopic study of X-ray-irradiated rabbit cornea

Abstract

Purpose To investigate the influence of ionizing radiation on the corneal epithelium and endothelium of rabbit eyes. Methods Five healthy mature albino rabbits were unilaterally irradiated with 20 Gy of X-rays (250 kV, 12 mA). Slit-lamp biomicroscopic observation and specular microscopic examination of the corneal epithelium and endothelium were carried out before and 1, 4,8,12,16,20,24, and 36 weeks after irradiation. We evaluated mean area of the superficial corneal epithelial cells, mean area and the percentage of hexagonal cells of the corneal endothelial cells, and corneal thickness. The statistical difference between the irradiated and control eyes was assessed using paired t-test. Results All animals developed cataract within 24 weeks. Slit-lamp biomicroscopy showed no apparent corneal abnormalities over the 36-week follow-up period. Specular microscopy revealed a significant enlargement of the superficial corneal epithelial cells from 4 to 12 weeks after irradiation (Po0.01), which disappeared at 16 weeks post-irradiation. Specular microscopy of the corneal endothelium showed enlargement and morphological alterations of the cells beginning 8 weeks after irradiation (Po0.05). These changes persisted throughout the study period. There were no statistically significant changes in corneal thickness. Conclusion After X-ray radiation of 20 Gy, transient damage occurred in the corneal epithelium, while delayed and irreversible changes were seen in the endothelium.

Methods of Assessment of the Corneas of the Eyes Laboratory Rabbits Exposed to Solar Ultraviolet‐B Radiation

“…Visualization of the corneal epithelial surface cells by slitlamp biomicroscopy (especially in rabbits) is difficult even with use of specular reflection techniques, but specially adapted instruments (with internal prisms to set the angle between the illumination source and the detector capturing the reflected light) have been developed either for in vivo assessments or applied to excised corneas . These specular microscopes can reveal the epithelial surface cells of the rabbit to allow for general descriptions to be made and, if the images are of very high quality, allow for the apparent sizes of the cells to assessed following irradiation (in one study with X‐rays) . A very different method has been used in UV‐B‐related studies in which the most superficial cells of the corneal epithelium are removed from the living eye onto a special filter membrane or paper.…”

Long-Term Changes in Rabbit Cornea After Ionizing Radiation

“…12 In the current study, we histopathologically investigated rabbit corneas 5 years after 20 Gy of irradiation. The corneal epithelium was found to be normal, but the endothelial cells exhibited morphologic abnormality, such as marked widening of intercellular space, anamorphosis of nuclei, partial loss of tight junctions, and formation of cytoplasmic processes bridging the adjacent endothelial cells.…”

“…Yao irradiated cultured rat kangaroo corneal endothelial cells and reported that breakdown of chromatin was observed 48 hours after high doses of x-irradiation. 11 We previously investigated the influence of 20 Gy of x-irradiation on rabbit cornea using specular microscopy 12 and found enlargement and morphologic alterations of the corneal endothelial cells beginning 8 weeks after irradiation. However, these changes did not disappear within the 36-week observation period, and thus, the long-term changes of the corneal endothelium after ionizing radiation remain unclear.…”

A current practice for predicting ocular toxicity of systemically delivered drugs

“…Lacrimal gland toxicity may be determined by abnormal tear production as estimated by use of Schirmer tear test papers, especially in dogs (90). Additional corneal evaluations include esthesiometry, which tests the sensitivity of the cornea (92,93), pachymetry, which measures the thickness of the cornea (94,95), keratometry, which measures corneal curvature (96,97), and specular microscopy for visualization of the corneal endothelium (94,98). These tests may be performed after the cornea has undergone an examination with a slit lamp biomicroscope.…”