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D. Luce, M. Shimmyo; Corneal Biomechanics Effects on the Measurement of Extremely Low and Negative Goldmann Calibrated IOP Using the Ocular Response Analyzer (ORA). Invest. Ophthalmol. Vis. Sci. 2009;50(13):4909.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate corneal biomechanical compensation for extremely low Goldmann equivalent IOP using the Reichert ORA.
Very low Goldmann equivalent IOP (Ocular Response Analyzer, IOPg < 1 mmHg) data for 12 eyes acquired in a regular clinical practice (M. Shimmyo, New York, NY) were analyzed to determine the effect of corneal biomechanical compensation using the ORA’s IOPg and IOPcc parameters. IOPg and IOPcc progression were evaluated for two subjects for which a significant number of time spaced measurements were available. The subject population clinical classification includes 9 POAG (primary open angle glaucoma), 1 dry eye and 2 normals.
For the 12 eyes, mean Goldmann equiavlent IOP (IOPg) was -1.40 mmHg, standard deviation, 1.29 mmHg, and range -4.98 to -.07 mmHg. Mean corneal compensated IOP (IOPcc) was +3.02, standard deviation 1.66 and range +0.2 to +6.3. In all cases the corneal compensated IOPcc was greater than zero. IOPcc showed a regular increasing "recovery" IOP for the two multiple measurement session patients following glaucoma surgery.
Measuring extremely low IOP, problematic with a Goldmann tonometer because of tear film and corneal mechanical properties, can be achieved with the Ocular Response Analyzer using its IOPcc parameter. The ORA’s non-contact and corneal compensation methodology effectively eliminates both tear film and corneal biomechanical influences on the IOPcc.
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