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RJ Watkins, P Gunvant, J Uddin, D Broadway; The Influence of Central Corneal Thickness & Corneal Curvature on Intraocular Pressure Measurement with the Goldmann Tonometer & the POBF Pneumotonometer . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3413.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Central corneal thickness (CCT) & corneal curvature influence intraocular pressure (IOP) measurement by Goldmann applanation tonometry (GAT). This study examined the influence of CCT & corneal curvature on IOP measurement using the Pulsatile Ocular Blood Flow (POBF) Pneumotonometer. Methods: 99 subjects from the Norwich glaucoma clinic were recruited, 40 with ocular hypertension, 27 with primary open angle glaucoma, 14 with normal tension glaucoma, 9 with combined mechanism glaucoma and 9 who were glaucoma suspects. IOP was measured using both GAT and POBF tonometry, the recordings being separated by 15 minutes, it being decided randomly which was performed first. After both IOP measurements, CCT was determined by BVI ultrasonic pachymetry (taking the lowest of 10 successive readings). K-readings were taken with a Keratron Optokon 2000 corneal topographer. Measurements were performed on both eyes of each subject and the eye included in the study was selected randomly. Results: For the whole data set, mean GAT IOP was 17.2mmHg (95%CI 16.2-18.2) and mean POBF IOP was 20.5mmHg (95%CI 19.4-21.6). Measurement of IOP by the two methods showed good correlation (Pearson r=0.84; p<0.0001) but with a systematic bias (mean intrasubject measurement difference was 3.3mmHg (95%CI 2.7-3.9)). Mean CCT was 530.9µ m (95%CI 523.6-538.2). Mean K reading was 7.1mm (95%CI 7.0-7.2). With both methods, measured IOP increased with increasing CCT (Pearson r=0.46; p<0.0001 for the POBF machine & r=0.38; p<0.0001 for GAT). Furthermore, the intrasubject IOP measurement difference also showed a positive relationship with increasing CCT (Pearson r=0.20; p=0.0423). There was a tendency for IOP measured using both techniques to be higher with steeper corneal curvatures but this was not statistically significant. There was no such trend for the methodologic difference in IOP measurement. Conclusion: IOP measurements with the POBF Pneumotonometer are influenced by CCT in the same way as GAT - thicker corneas are associated with higher IOP measurements.
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