Intraocular pressure (IOP) measurement differences with Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) are affected by atmospheric pressure inside a hyperbaric chamber.
To compare IOP measurements obtained with GAT and DCT in 22 normal individuals at different atmospheric pressures simulated in a hyperbaric chamber.
The IOP of both eyes of 22 healthy volunteers was measured using GAT and DCT at 4 different atmospheric pressure levels.
Starting at 1 Queretaro atmospheric pressure (QATM), the IOP was measured with GAT and DCT. The atmospheric pressure was then increased to 1.1 QATM (equivalent to 1032 m above sea level), 1.2 QATM (equivalent to 315 m above sea level), and 1.25 QATM (equivalent to sea level), starting 5 minutes after reaching each level. The limits of agreement between various measurements with each tonometer were calculated using the Bland-Altman plots.
The first 4 subjects were used to measure feasibility, consistency, variability, and the time needed for IOP to return to baseline after each atmospheric pressure increase.
For the entire 44 eyes, the mean GAT IOP at 1 QATM was 12.23 mm Hg (range, 8 to 20 mm Hg; SD, 2.84) and mean DCT was 16.36 (range, 12.1 to 25.3; SD, 2.84), with a mean 4.14 mm Hg difference (range, −0.1 to 7.5 mm Hg; SD, 1.62; P<0.001).
Using the second measurements of the first 4 subjects and those after 5 minutes of adaptation for the rest of the group at 1.1 QATM, mean GAT IOP was 11.05±2.68 mm Hg and mean DCT IOP was 15.60±3.02 mm Hg, for a mean difference between instruments of 4.56±1.81 mm Hg (P<0.001).
At 1.2 QATM, mean GAT IOP was 11.14±2.53 mm Hg and mean DCT IOP was 15.39±2.91 mm Hg. The difference between instruments was 4.25±2.12 mm Hg (P<0.001).
At 1.25 QATM, the mean GAT IOP was 12.39±3.11 mm Hg and mean DCT IOP was 14.91±2.73 mm Hg. The difference between instruments after 5 minutes of adaptation was 2.53±1.62 mm Hg (P<0.001).
Generalized estimating equations for performing linear regression multivariable analysis using atmospheric pressure, expressed as altitude, and age as covariates, shows that the difference between GAT and DCT increases by 1 mm Hg per 673 m of increase of altitude above sea level. Age was not a significant predictor.
Acute changes in atmospheric pressure induce changes in IOP measurements for both GAT and DCT and in different directions. Despite the limitation of sample size, it may be postulated that the difference of IOP measurements between the 2 tonometers increases with lower atmospheric pressures.