Correlation between corneal and scleral pneumatonometry: an alternative method for intraocular pressure measurement.

Purpose: To evaluate scleral pneumatonometry as an alternative method for measuring intraocular pressure (IOP).
Design: Prospective cross-sectional study.
Methods: Adult subjects with healthy eyes were recruited from the Comprehensive Eye Service at the University of Illinois Eye and Ear Infirmary from August 2008 through February 2009. Study measurements included corneal pneumatonometry (IOPk), scleral pneumatonometry (IOPs), axial length (AL), spherical equivalent (SE), and central corneal thickness (CCT). Main outcome measures were scleral IOP and corneal IOP.
Results: Analysis included a monocular data set from single eyes of 97 subjects (age: 18-82 years). IOPs was consistently higher than IOPk, and correlated positively with IOPk (r = 0.57, P < .0001), age (r = 0.51, P < .0001), and SE (r = 0.32, P = .0002). The difference between scleral and corneal IOP (IOPs - IOPk) correlated positively with IOPs (r = 0.89, P < .0001), age (r = 0.57, P < .0001), and SE (r = 0.34, P < 0.0001). Bland-Altman analysis for agreement between scleral and corneal pneumatonometry measurements showed a mean difference of 8.08 mm Hg, with the 95% limit of agreement between -3.47 and 19.64 mm Hg. Regression analysis yielded the following equation: IOPk = 11.9 + 0.32(IOPs) - 0.05(Age).
Conclusions: Scleral pneumatonometry correlates positively with corneal pneumatonometry and is more accurate at lower values and in younger patients. When adjusted for age, scleral pneumatonometry may be an adequate alternative in situations where corneal measurements are impractical.
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