Corneal opacity, hydration and endothelial morphology in the bovine cornea opacity and permeability assay using reduced treatment times.

The purpose of this study was to determine whether the standard bovine cornea opacity and permeability (BCOP) assay exposure time of 10 minutes overestimates the ocular irritancy of chemical substances. Corneas were subjected to BCOP protocol following 30-second and 1-minute exposures to irritants. Corneal opacity and hydration (mg H(2)O/mg cornea) were then measured and compared to data obtained after 10 minute irritant treatments. For most test substances corneal opacity and hydration were lower following reduced exposure times. It is suggested that using shorter exposure times in BCOP protocol may be more predictive of human response to ocular irritants, since irritants are usually in brief contact with the ocular surface during accidental exposure. A second purpose of this study was to examine effects of irritants on the corneal endothelium. Corneas were treated according to BCOP protocol following exposure to irritants for 1 or 10 minutes. The endothelium was stained with Alizarin Red and trypan blue, and examined using light microscopy. Severe irritants, such as NaOH and trichloroacetic acid, cause endothelial cell death. It was also determined that simply mounting the cornea in the BCOP assay holders caused damage to 20% of the endothelial cells. Because the endothelium is essential for normal corneal transparency and hydration, it is suggested that examination of the endothelium be added to the BCOP assay and that optimization of the assay will require modification of the cornea holders.