Goldmann and error correcting tonometry prisms compared to intracameral pressure

Abstract

BackgroundCompare Goldmann applanation tonometer (GAT) prism and correcting applanation tonometry surface (CATS) prism to intracameral intraocular pressure (IOP), in vivo and in vitro.MethodsPressure transducer intracameral IOP was measured on fifty-eight (58) eyes undergoing cataract surgery and the IOP was modulated manometrically to 10, 20, and 40 mmHg. Simultaneously, IOP was measured using a Perkins tonometer with a standard GAT prism and a CATS prism at each of the intracameral pressures. Statistical comparison was made between true intracameral pressures and the two prism measurements. Differences between the two prism measurements were correlated to central corneal thickness (CCT) and corneal resistance factor (CRF). Human cadaver eyes were used to assess measurement repeatability.ResultsThe CATS tonometer prism measured closer to true intracameral IOP than the GAT prism by 1.7+/−2.7 mmHg across all pressures and corneal properties. The difference in CATS and GAT measurements was greater in thin CCT corneas (2.7+/−1.9 mmHg) and low resistance (CRF) corneas (2.8+/−2.1 mmHg). The difference in prisms was negligible at high CCT and CRF values. No difference was seen in measurement repeatability between the two prisms.ConclusionA CATS prism in Goldmann tonometer armatures significantly improve the accuracy of IOP measurement compared to true intracameral pressure across a physiologic range of IOP values. The CATS prism is significantly more accurate compared to the GAT prism in thin and less rigid corneas. The in vivo intracameral study validates mathematical models and clinical findings in IOP measurement between the GAT and CATS prisms.

Intraocular Pressure Measurement Accuracy and Repeatability of a Modified Goldmann Prism: Multicenter Randomized Clinical Trial

“…A previously completed cadaver eye study demonstrating statistical equivalence was better suited to assess intra-operator and same eye inter-operator measurement variability. 15 …”

“…18 The results verify the previously published mathematical modeling, direct CATS/GAT comparisons and intracameral IOP comparisons examining the difference between CATS and GAT measurements when correlated to corneal thickness. 12,13,14,15,16 There are several other tonometers which have been compared to GAT to demonstrate substantial equivalence for FDA clearance. Since the scope of this study was a direct comparison to the GAT reference tonometer and the CATS prism is simply a replacement part for the GAT, no comparison to other tonometers was completed.…”

“…Although previous studies on the CATS prism did show statistically significant CATS minus GAT IOP correlation to corneal hysteresis and corneal resistance factor measured by an Ocular Response Analyzer (ORA- Reichert, Depew, NY). 13,15 …”

“…The CATS prism has demonstrated improved IOP accuracy mathematically and by direct GAT comparison, as well as by comparison to transducer intracameral pressure. 12,13,14,15,16 …”

“…Sensitivity to the corneal biomechanical error parameters is reduced by partially matching the negative curvature of the tonometer to positive curvature of the cornea. 12,13,14,15,16 The scientific premise of the CATS tonometer prism is a minimization of the intra-corneal stress during applanation. The reduced intra-corneal stress minimizes the contribution of the corneal deformation to the total force on the prism face thus measuring predominantly the force due to IOP.…”