Abstract
Purpose :
Changes to the air jet delivery and applanation detection systems in the newest generation Ocular Response Analyzer (G3 ORA) altered the morphology of its output waveform, compared to the original device (G1 ORA). This study quantified differences in intraocular pressure (IOP) and biomechanical parameters both between the devices and between subjects with keratoconus and controls.
Methods :
Case subjects with keratoconus (n = 31 eyes) and healthy control subjects (n = 193 eyes) were prospectively recruited. Four measurements of corneal-compensated intraocular pressure (IOPcc), Goldmann-correlated intraocular pressure (IOPg), corneal hysteresis (CH), and corneal resistance factor (CRF) were collected in both eyes with both the G3 and the G1 ORAs. Inter-device measurement order was randomized, and the measurement with the highest waveform score from each eye was analyzed. Paired t-tests compared results between the ORAs, and t-tests compared results between the cohorts (significance threshold α = 0.05). Values are mean ± standard deviation.
Results :
In the cases, CH (inter-device difference = 0.52 ± 1.35 mmHg) and CRF (0.58 ± 1.26 mmHg) were significantly higher (p = 0.04 and p = 0.02, respectively) in the G3 ORA than in the G1 ORA. In the controls, IOPg (0.62 ± 2.03 mmHg), CH (0.34 ± 1.02 mmHg), and CRF (0.47 ± 0.84 mmHg) were all significantly higher (p < 0.001 for all) in the G3 ORA than in the G1 ORA. IOPcc did not differ between the devices in cases or in controls. IOPg, IOPcc, CH, and CRF were significantly higher in cases than in controls for both ORAs (Figure).
Conclusions :
Our results suggest that the air jet delivery and applanation detection system changes incorporated in the G3 ORA did alter its assessment of biomechanical parameters, compared to the G1 ORA. IOP outcomes were less effected. Therefore, caution must be taken when comparing results between the two generations of ORAs. Despite these differences between the devices, the ORA G3 consistently was able to detect significant differences between the cases and the controls, supporting its value in managing keratoconus. The next step in this research is to adapt the Keratoconus Match Index metric for the G3 model.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.