Investigation of the effect of solution pH value on rabbit corneal stroma biomechanics.

ABSTRACT

PURPOSE: To facilitate the protection of corneal stability during corneal epithelium defects by determining the effect of solution pH on corneal stroma biomechanics. METHODS: Thirty rabbit corneas were extracted, and the epithelium was scraped off. The samples were immediately subjected to inflation tests with pressures ranging from 0.3 to 6 kPa at baseline and in three subsequent test cycles. During a 10-min interval between cycles, specimens were randomly divided into four groups; in three of these groups, phosphate-buffered saline (PBS) drops with pH values of 6.9, 7.4, or 7.9 were applied to the surface once per minute, whereas the fourth group did not receive drops. RESULTS: The corneal thickness significantly increased following the administration of PBS, while the corneal tangent modulus significantly decreased. At 2.5 and 4.5 kPa, the modulus reduction was significantly smaller in the specimens treated with pH 6.9 PBS than in those treated with pH 7.4 or 7.9 PBS, adjusted for changes in corneal thickness. Linear fitting of the pressure-modulus plot revealed that the regression coefficient significantly decreased over time. The reduction in the coefficient was most prominent in the PBS-treated groups, and the administration of pH 6.9 PBS elicited the smallest reduction among those three groups, adjusted for corneal thickness changes. CONCLUSION: The study demonstrated that the administration of PBS drops with various pH values affected corneal biomechanics independent of corneal stromal swelling, and the impact of slightly acidic PBS was minimal. The effect became more prominent as posterior pressure increased. The research provides the basis for mediating the pH value of tear film and drops to maintain biomechanical stability of epithelium defects corneal stroma.