Evaluation of the relationship of corneal biomechanical metrics with physical intraocular pressure and central corneal thickness in ex vivo rabbit eye globes

Abstract

The relationship of corneal biomechanical metrics provided by the Ocular Response Analyzer (ORA) and Corvis ST (CVS) with physical intraocular pressure (IOPp) and central corneal thickness (CCT) was evaluated. Thirty fresh enucleated eyes of 30 rabbits were used in ex vivo whole globe inflation experiments. IOPp was measured with a pressure transducer and increased from 7.5 to 37.5 mmHg in steps of 7.5 mmHg while biomechanical data was acquired using the ORA and CVS. At least 3 examinations were performed at each pressure level, where CCT and twelve biomechanical metrics were recorded and analyzed as a function of IOPp. The biomechanical metrics included corneal hysteresis (CH) and corneal resistance factor (CRF), obtained by the ORA. They also included the applanation times (A1T, A2T), lengths (A1L, A2L) and velocities (A1V, A2V), in addition to the highest concavity time (HCT), peak distance (PD), radius (HR) and deformation amplitude (DA), obtained by the CVS. The variation of CCT and the twelve biomechanical metrics for the 30 rabbit eyes tested across the 5 pressure stages considered (inter-pressure differences) were statistically significant (P = 0.00). IOPp was highly to moderately correlated with most biomechanical metrics, especially CRF, A1T, A1V, A2V, PD and DA, while the relationships with CH, A2T, A1L and HCT were poor. IOP has important influences on most corneal biomechanical metrics provided by CVS and ORA. Two biomechanical metrics A1V and HR were influenced by CCT after correcting for the effect of IOP in most pressure stages, while the correlation with others were weak. Comparisons of research groups based on ORA and CVS with different IOPs and CCTs may lead to possible misinterpretations if both or one of which are not considered in the analysis.