Measuring accurate IOPs: Does correction factor help or hurt?

Pinakin Gunvant¹, Robert D Newcomb², Elliot M Kirstein³, Victor E Malinovsky⁴, Richard J Madonna⁵, Richard E Meetz ⁴

¹Southern College of Optometry, Memphis, Tennessee, USA; ²The Ohio State University College of Optometry, Columbus, Ohio, USA; ³The Glaucoma and Diabetes Eye Institute, Cincinnati, Ohio, USA; ⁴Indiana University School of Optometry, Bloomington, Indiana, USA; ⁵State University of New York College of Optometry, New York, USA

Purpose: To evaluate if using the Ehlers correction factor on the intraocular pressure (IOP) measured using the Goldmann applanation tonometer (GAT) improves its agreement with the PASCAL dynamic contour tonometer (DCT).

Patients and methods: A total of 120 eyes of 120 individuals were examined. Participants underwent IOP measurement with both the DCT and the GAT and central corneal thickness measurement. The Ehlers correction factor was applied on the GAT IOP measurements to calculate Ehlers-corrected GAT IOP. The agreement between the DCT and GAT, and DCT and Ehlers-corrected GAT IOP was analyzed. The analyses were repeated by stratifying the data by race.

Results: The mean IOP of the GAT, DCT, and the Ehlers-corrected GAT was 15.30, 16.78, and 14.68 mmHg, respectively. The agreement as assessed by Bland–Altman plot for the GAT with the DCT and DCT and Ehlers-corrected GAT IOP was +4.1 to −6.9 and +4.15 to −8.25 mmHg, respectively. The results were similar even when stratifying the data by race.

Conclusion: Using Ehlers correction factor to account for the effect of corneal parameters on the IOP measured by the GAT worsens the agreement with the DCT. This effect remains even when stratifying the data by race.

Keywords: dynamic contour tonometer, Goldmann applanation tonometer, tonometric correction factors, central corneal thickness, intraocular pressure