Correction factors for Goldmann Tonometry.

Area of Science:

• Ophthalmology
• Biomedical Engineering
• Optometry

Background:

• Intraocular pressure (IOP) measurement is crucial for diagnosing and managing glaucoma.
• The Goldmann Applanation Tonometer (GAT) is a standard tool, but its accuracy can be affected by corneal properties.
• Correction factors aim to improve the precision of IOP readings.

Purpose of the Study:

• To evaluate the in vitro accuracy of different correction factors.
• To assess the effectiveness of these factors in reducing measurement errors with the GAT.
• To compare the performance of various established correction equations.

Main Methods:

• Donor corneas were subjected to simulated in vivo true IOP (IOPT) using an inflation test rig.
• Central corneal thickness and curvature were measured.
• IOP was measured using GAT at 25 pressure levels (5-45 mm Hg).
• Five correction equations (Elsheikh, Ehlers, Chihara, Shimmyo et al., Orssengo and Pye) were applied to GAT readings.

Main Results:

• Uncorrected GAT measurements showed a mean error of +2.25±0.62 mm Hg.
• Elsheikh and Chihara equations reduced mean errors to +0.78±0.62 and +1.08±0.61 mm Hg, respectively.
• Ehlers, Shimmyo et al., and Orssengo and Pye equations resulted in overcorrection, with mean errors of -0.75±2.28, -1.27±1.85, and -0.77±1.83 mm Hg.

Conclusions:

• The Elsheikh and Chihara et al. equations significantly decreased GAT IOP measurement errors compared to IOPT.
• These two equations demonstrated greater consistency than other tested correction factors.
• The Elsheikh and Chihara equations show potential clinical utility for estimating true IOP.