Changes in Corneal Biomechanics and Applanation Tonometry with Induced Corneal Swelling

PURPOSE: To investigate the changes in Goldmann applanation tonometry (GAT) and Ocular Response Analyzer (ORA) measurements with corneal edema induced by contact lenses. METHODS: Twenty-five healthy, normal subjects (age, 23 ± 2 years) had central corneal radius (CCR), ORA, GAT, and central corneal thickness (CCT) measurements performed in both eyes before a thick, soft hydrogel contact lens was worn with eye closure for 2 hours in one eye. Measurements were repeated immediately after lens removal and every 20 minutes thereafter for the following hour. RESULTS: The experimental and control eyes behaved asymmetrically over time (repeated measures analysis of variance [RMANOVA]; P < 0.05) for all variables except CCR. GAT, ORA Goldmann-correlated intraocular pressure (ORAg), and ORA corneal-compensated intraocular pressure (ORAcc) showed comparable overestimations, whereas corneal hysteresis (CH) and corneal resistance factor (CRF) responded to corneal swelling in dissimilar ways (RMANOVA; α = 0.05). The variation in GAT in experimental eyes could be predicted by changes in CRF (0.85 [0.23] mm Hg ΔGAT/mm Hg ΔCRF; P < 0.001), but not by CCT or CH. The covariation of both CH and CRF with CCT was influenced by the presence of corneal swelling (Eye×ΔCCT interaction, P < 0.001 and P = 0.003, respectively). CONCLUSIONS: The GAT overestimation caused by small amounts of corneal swelling represents an overall increase in corneal rigidity, which is partially characterized by CRF. In contrast, CH does not appear to usefully quantify biomechanical changes induced by corneal swelling. The accuracy of ORAcc is affected by corneal swelling.