OPA – An other Glaucoma Parameter

PASCAL measures IOP 100 times per second, recording the dynamics of the heart rate and the ocular pulse curve.

Influence of corneal properties on GAT

"Measurement of Intraocular Pressure:1. On average, greater central corneal thickness (CCT) results in overestimation of intraocular pressure (IOP) as measured by Goldmann applanation tonometry (GAT). […]

2. Compared to GAT, CCT has a lesser effect on IOP measured by DCT and the OcularResponse Analyser (ORA), CCT has a greater effect on IOP measured by NCT and Rebound Tonometry. […]

6. A thick cornea gives rise to a greater probability of an IOP being over-estimated (and a thin cornea of an IOP being under-estimated), but the extent of measurement error in individual patients cannot be ascertained from the CCT alone. […]

8. The corneal modulus of elasticity likely has a greater effect on GAT IOP measurement error than CCT.”



R. Weinreb, J. Brandt, D. Garway Heath, F. Medeiros

4th World Glaucoma Consensus on IOP Consensus Points, 2006

IOP and OPA

The Ocular Pulse Amplitdue OPA is the difference between systolic and diastolic IOP stemming from vascular influences.

OPA in different glaucoma groups18

Ocular Pulse amplitude is reduced in patients with NTG or POAG as compared to healthy individuals and OHT.




References:

18 N. Pfeiffer et al. OPA in patients with POAG, NTG, and OHT; (Br J Ophthalmol 2002;86:981–984)