 Goldmann applanation tonometry Haag-Streit AG, Koeniz, Switzerland is still recognized as the gold standard for measuring IOP in glaucoma patients and it was performed in all patients at all visits. The ORA takes the CH and CRF measurements into account to generate the corneal-compensated intraocular pressure IOPcc value, which is mean to be less affected by corneal biomechanical properties than the Goldmann-IOP. The IOP bias is estimated as the difference between IOPcc and Goldmann-IOP IOPcc - Goldmann IOP. A positive bias value indicates that the IOPcc is larger than the Goldmann-IOP, meaning that Goldman tonometry underestimated IOP in comparison to the IOPcc. 