Goldmann applanation tonometry error relative to true intracameral intraocular pressure in vitro and in vivo

Abstract

Background: Goldmann applanation tonometry (GAT) error relative to intracameral intraocular pressure (IOP) has not been examined comparatively in both human cadaver eyes and in live human eyes. Futhermore, correlations to biomechanical corneal properties and positional changes have not been examined directly to intracameral IOP and GAT IOP. Methods: Intracameral IOP was measured via pressure transducer on fifty-eight (58) eyes undergoing cataract surgery and the IOP was modulated manometrically on each patient alternately to 10, 20, and 40 mmHg. IOP was measured using a Perkins tonometer in the supine position on 58 eyes and upright on a subset of 8 eyes. Twenty one (21) fresh human cadaver globes were Intracamerally IOP adjusted and measured via pressure transducer. Intracameral IOP ranged between 5 and 60 mmHg. IOP was measured in the upright position with a Goldmann Applanation Tonometer (GAT) and supine position with a Perkins tonometer. Central corneal thickness (CCT) was also measured. Results: The Goldmann-type tonometer error measured on live human eyes was 5.2 +/−1.6 mmHg lower than intracameral IOP in the upright position and 7.9 +/− 2.3 mmHg lower in the supine position (p < .05). CCT also indicated a sloped correlation to error (correlation coeff. = 0.18). Cadaver eye IOP measurements were 3.1+/−2. 5 mmHg lower than intracameral IOP in the upright position and 5.4+/− 3.1 mmHg in the supine position (p < .05).

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

“…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.…”

“…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.…”

Goldmann and error correcting tonometry prisms compared to intracameral pressure

“…It is the primary metric in the diagnosis and treatment of glaucoma as well as many other pressure related processes [ 1 – 4 ]. Central corneal thickness (CCT) correction is the only common clinical correction for the several identified GAT IOP corneal biomechanical measurement errors [ 5 – 10 ]. CCT IOP error correction has been shown to be inadequate by itself [ 11 , 12 ].…”

Biomechanik und Augeninnendruck bei Hornhauterkrankungen

“…Problematisch sind hierbei u. a. die vielen verschiedenen Messmethoden, die in unterschiedlichen Kombinationen miteinander verglichen werden und ebenso die fehlende eindeutige Referenz. Als Standard wird zwar immer die GAT herangezogen, im Vergleich mit intrakameralen Messungen zeigen sich jedoch auch für diese Methode falsch niedrige Abweichungen um teils mehrere mmHg [8,10,31]. Die GAT wird ihren Stellenwert als Goldstandard trotz dieser Abweichungen vermutlich auch weiterhin behalten und so als Ersatzreferenz für invasive Messungen dienen.…”