Precision of ocular response analyzer

To evaluate the repeatability of corneal hysteresis (CH) and corneal resistance measurements as well as the consistency of the four shots within each measurement using the ocular response analyzer (ORA, Reichert Ophthalmic Instruments, Depew, NY) and to generate a pool of data of a normal population.

A total of 45 eyes from 45 healthy volunteers without ocular pathologies and normal visual acuity were enrolled in this study. A sequence of five consecutive measurements was performed with each patient with the ORA. The biomechanical properties of the cornea in terms of CH and corneal resistance factor (CRF) were recorded, as well as the Goldmann-correlated IOP (IOPg) and cornea correlated IOP (IOPcc). The trend in each measurement sequence was analyzed and Cronbach's α was derived for the repeatability. The average of four shots within each measurement was compared with the best signal value (BSV) provided by the internal data processing of the ORA.

Mean value for CH was 11.58 and BSV was 11.55. For CRF, mean value was 11.21 and BSV was 11.28. No significant difference was found between the average value and the BSV of one measurement (p > 0.05). No significant difference was found between the average value and the BSV of the five consecutive measurements, only IOPg showed a significant difference (p = 0.017), average value of IOPg is higher than BSV. Within a sequence of five measurements for each individual, the average values of the four shots per measurement for IOPg and IOPcc are decreasing by 1.19 and 1.05 mmHg on average. The repeatability test revealed good results for CH and CRF (all α are higher than 0.9).

The ORA provides, beside intraocular pressure additional, information about the biomechanical properties of the cornea such as hysteresis and resistance. It proves to yield good repeatability for corneal hysteresis and resistance in normal subjects.