The effect of corneal biomechanical properties on rebound tonometer in patients with normal-tension glaucoma

Purpose To evaluate the effects of corneal biomechanical properties on intraocular pressure (IOP) measured with the ICare, and to compare IOP readings obtained with ICare, Ocular Response Analyzer (ORA), and Goldmann applanation tonometry (GAT) in normal-tension glaucoma (NTG) and normal subjects. Design Prospective, cross-sectional, comparative study. Methods IOP was measured with ICare, ORA, and GAT. All subjects had corneal hysteresis (CH) and corneal resistance factor (CRF), which were measured with ORA; and central corneal thickness (CCT), axial length, spherical equivalent, and keratometry. Results This study enrolled 97 eyes of 97 NTG patients and 89 eyes of 89 normal subjects. CCT, CH, and CRF in NTG patients were significantly lower than those in normal subjects (P =.033, P =.006, and P =.003). The difference in IOP between techniques was highly significant in NTG patients (P <.001), while there was no significant difference in IOP values between techniques in normal controls (P =.931). ICare readings were significantly lower than corneal-compensated IOP in NTG patients (P =.014). CH and CRF were significantly associated with IOP measurements with ICare in NTG and normal subjects (P <.001). The greater difference between IOPcc and ICare in NTG patients was significantly influenced by the lower CH (P <.001). Conclusions Since ICare is a convenient way to measure IOP, ICare is a reasonable option as an alternative tonometer in NTG patients. However, the clinician must consider that the corneal biomechanical characteristics in NTG can cause ICare to underestimate IOP.