Central and peripheral intraocular pressure measured by a rebound tonometer

Tsutomu Yamashita¹, Atsushi Miki^1,2,3, Yoshiaki Ieki², Junichi Kiryu², Kiyoshi Yaoeda^3,4, Motohiro Shirakashi^3,5
1Department of Sensory Science, Faculty of Health Science and Technology, Kawasaki University of Medical Welfare, ²Department of Ophthalmology, Kawasaki Medical School, Kurashiki, Okayama, Japan; ³Division of Ophthalmology and Visual Sciences, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan; ⁴Yaoeda Eye Clinic, Nagaoka, Japan; ⁵Kido Eye Clinic, Niigata, Japan

Purpose: We investigated at which corneal region the intraocular pressure as measured by the Icare^® rebound tonometer (Finland Oy, Espoo, Finland) (hereinafter referred to as IC) was closest to the intraocular pressure as measured by the Goldmann applanation tonometer (hereinafter referred to as GT). We also investigated which parameters would be best for preparing the most suitable model for predicting GT.
Methods: A total of 102 normal eyes in 102 subjects were enrolled. IC measurements were carried out at the central, superior, inferior, temporal, and nasal regions of the cornea (ICC, ICS, ICI, ICT, and ICN, respectively), followed by GT calculations. Differences between GT and IC were analyzed using the Bland–Altman method. Stepwise multiple regression analysis was performed using GT as the objective variable, and age, laterality of eye, spherical equivalent refractive error, corneal radius, axial length, central corneal thickness, GT, ICC, ICS, ICI, ICT, and ICN as the explanatory variables.
Results: IC was higher than GT at all of the corneal regions, but the region with the least bias was ICC, followed by ICT. In the multiple regression analysis, the following prediction formula was calculated: GT = (0.445 × ICC) + (0.198 × ICN) + 3.022. When ICC was excluded from the explanatory variables, ICT had the highest partial correlation coefficient with GT.
Conclusion: ICC was closest to GT, but GT could be explained better by adding ICN to the prediction model. Moreover, in instances where ICC cannot be calculated or where reliability is clearly poor due to abnormal ocular rigidity, ICT was the closest to GT measured in the central corneal region.

Keywords: IOP, Icare, Goldmann applanation tonometer, ocular rigidity