Abstract
Purpose :
This study was designed to compare intraocular pressure (IOP) measurements taken using Goldmann Applanation Tonometry (GAT) with those obtained by the Falck Multifunctional Device (FMD, Falck Medical, CT, USA), to evaluate their respective accuracy and reliability.
Methods :
For the GAT measurement, IOP was assessed three times at intervals of 30 seconds (Average IOP GAT) in each eye. Subsequently, Central Corneal Thickness (CCT) was measured using a pachymeter (Pachmate 2, DGH Technology, Exton, PA, USA). Following this, IOP measurements were taken serially with the FMD in each eye. The device calculated an average IOP for each eye (IOP FMD), which was accepted for analysis only if the calculated variability was less than 10%. Additionally, Ocular Pulse Amplitude (OPA), which is the difference in IOP between systolic and diastolic phases, was recorded. Notably, GAT measures IOP predominantly during diastole. Therefore, to correct for systolic contributions, half of the OPA value was subtracted from the IOP FMD (Corrected IOP FMD).
Results :
The study included a total of 40 eyes from 21 patients, with a gender distribution of 57% male and 43% female. The participants had a mean age of 63.7 years. The mean Average IOP GAT was 15.2 mm Hg, with a mean CCT of 561.4 µm. In contrast, the mean Corrected IOP FMD was found to be 16.3 mm Hg. This resulted in a significant difference of 1.1 mm Hg, with the Corrected IOP FMD being higher (p-value = .029). When corrected for CCT variations, the Mean Average IOP GAT adjusted to 14.4 mm Hg, leading to a discrepancy of 1.9 mm Hg (p = 0.01).
Conclusions :
The study reveals that GAT, which operates on the premise of measuring IOP on a very thin and elastic membrane during diastole, inherently harbors sources of variability. It fails to take into account factors such as capillary forces affecting the moist corneal surface and the elasticity of corneal tissue. Consequently, GAT consistently underestimates IOP when compared to FMD measurements. This underestimation persists even after adjustments for corneal thickness and the systolic portion of the cardiac cycle are accounted for. The FMD, on the other hand, includes an algorithm that compensates for corneal wetness, tissue elasticity, and systolic variation during the cardiac cycle, thus potentially offering a more accurate and reliable method for IOP measurement.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.