Midperipheral corneal thickness affects noncontact tonometry

Area of Science:

• Ophthalmology
• Biomedical Optics
• Corneal Biomechanics

Background:

• Intraocular pressure (IOP) is a key metric in glaucoma diagnosis and management.
• Noncontact tonometry (NCT) is a common method for measuring IOP.
• Central corneal thickness (CCT) is known to influence IOP measurements.

Purpose of the Study:

• To investigate the influence of midperipheral corneal thickness (MCT) on IOP measurements obtained via NCT.
• To determine if MCT provides additional predictive value for IOP beyond CCT.

Main Methods:

• Corneal thickness profiles (5-mm diameter) and IOP were measured in 51 healthy subjects using Orbscan IIz and Topcon CT-80 NCT.
• Pearson correlation and linear regression analyses assessed relationships between corneal thickness and IOP.

Main Results:

• IOP correlated with CCT (r=0.445) and MCT at all midperipheral locations (r=0.357-0.527).
• Midperipheral increase in corneal thickness (MICT) at 2.5-mm temporal to the center, along with CCT, best predicted IOP (r=0.563).
• Both CCT and MICT independently affected IOP, with MICT showing a larger effect per 10 µm increase (1.03 mm Hg vs. 0.37 mm Hg for CCT).

Conclusions:

• Midperipheral corneal thickness, particularly in the temporal cornea, exerts a clinically significant and independent effect on NCT-based IOP measurements.
• Accurate IOP assessment may require considering both central and midperipheral corneal thickness variations.