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Ocular pulse amplitude may reduce reliability of Goldmann applanation tonometry
J Glaucoma. 2011;20(6):344-349.
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Ocular pulse amplitude may diminish the accuracy and reliability of Goldmann applanation tonometry, a study found.
The Ocular Response Analyzer (ORA, Reichert) was used to measure Goldmann-correlated IOP (IOPg), corneal-compensated IOP (IOPcc), corneal hysteresis (CH) and corneal resistance factor (CRF). A dynamic contour tonometer (DCT, Pascal, Swiss Microtechnology) was used to gauge ocular pulse amplitude (OPA).
"The measurement reliability of ORA was only moderate," the authors said. "Eyes with large OPA were associated with high IOP measurement variability. Taking average of multiple repeated measurements is important for reliable measurement of ORA."
Investigators assessed the variability of ORA measurement and its relationship to OPA. They hypothesized that eyes with a large OPA would show increased variability in ORA measurement.
The prospective study included 60 patients with glaucoma and 60 non-glaucomatous controls. One randomly selected eye of each patient underwent repeated ORA and OPA measurements.
Study results showed repeatability values of 4.08 mm Hg for IOPg, 4.72 mm Hg for IOPcc, 2.14 mm Hg for CRF and 2.35 mm Hg for CH in non-glaucomatous eyes.
Repeatability values were 4.18 mm Hg for IOPg, 5.56 mm Hg for IOPcc, 2.17 mm Hg for CRF and 2.78 mm Hg for CH in glaucomatous eyes.
IOPcc, IOPg, and DCT IOP correlated with OPA in both normal and glaucomatous eyes. Within-subject variations in IOPg and IOPcc correlated strongly with OPA, the authors said.
The Ocular Response Analyzer (ORA) is a tonometry device touted to provide a better assessment of IOP because it is not as subject to the biomechanical aspects of the cornea as Goldmann applanation tonometry. Xu et al found that in eyes with large ocular pulse amplitudes, the repeatability of ORA measurements of IOP was poor, likely due to the rapid assessment of IOP and thus being subject to the fluctuations that result from the cardiac cycle. During Goldmann applanation, the same phenomena is seen as pulsating mires. This group’s finding is highly significant as it points to the need to take repeat ORA measurements in order to obtain a more accurate assessment of IOP. One concern is that it is not possible to know which patients, a priori, have a large ocular pulse amplitude.
– Douglas J. Rhee, MD
OSN Glaucoma Board
Member
Disclosure: Dr. Rhee has no relevant financial disclosures.