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Jong-Hoon Shin, Jiwoong Lee, Eun Ah Kim, Joseph Caprioli; The Effect of Corneal Biomechanical Properties on Rebound Tonometer in Patients with Normal Tension Glaucoma. Invest. Ophthalmol. Vis. Sci. 2014;55(13):145.
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To evaluate the effects of corneal biomechanical properties on intraocular pressure (IOP) measurements with ICare and to compare IOP measurements with ICare, ORA and GAT in patients with normal tension glaucoma (NTG)
IOP was measured in both NTG patients and normal subjects with ICare, Ocular response analyzer (ORA), and Goldmann applanation tonometry (GAT) by a single observer. All subjects had corneal hysteresis (CH) and corenal resistance factor (CRF) measurements which were obtained with ORA, central corneal thickness (CCT), axial length (AXL), spherical equivalent (SE), and corneal curvature (K).
This study enrolled ninety-seven eyes of ninety-seven patients with NTG and eighty-nine eyes of eighty-nine normal subjects.CCT, CH and CRF in NTG patients were significantly lower than in normal subjects (P = 0.033, 0.006, 0.003, respectively). In both NTG and normal control, IOP readings with ICare were not significantly different with IOPcc, IOPg and GAT. There was no significant difference in IOP levels with ICare, IOPcc, IOPg, and GAT between two groups. However, the difference between ICare readings and IOPcc in NTG patients was significantly higher than in normal subjects (P = 0.018). In multiple regression analysis, CH and CRF were significantly associated with IOP measurements with ICare in NTG patients and normal subjects (P<0.001, adjusted R2= 0.580, P<0.001, adjusted R2= 0.534, respectively). In the Bland-Altman plot comparing agreements between two IOP parameters, there was reasonable agreement in both groups.
Since ICare is a convenient way to measure IOP, ICare is a reasonable option as an alternative tonometer in NTG. However, the clinician must consider that differenct corneal biomechanical factors in NTG patients can cause ICare to underestimate IOP.
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