Time duration between « in » and « out » signal peaks of the ocular response analyser in normal and keratoconic eyes.

Purpose Compare time duration between « in » and « out » signal peaks extracted from the signal curves of the ocular response analyser (ORA; Reichert Ophthalmic Instruments, Buffalo, NY, USA) in keratoconic eyes and in a control group without keratoconus. Methods This retrospective, comparative case series comprised 23 patients with keratoconus and 54 age- and sex- matched controls who underwent a complete clinical eye examination, corneal topography, and biomechanical evaluation. Corneal hysteresis (CH), corneal resistance factor (CRF), and time duration between « in » and « out » signal peaks were compared between the two groups. Every patient was subjected to examination (between 3 and 5/per eyes) by the ORA. Results Corneal hysteresis was 8.58+/- 1,82 mmHg (range: 5.21 to 17.1 mmHg) in the keratoconus group and 10.54+/- 1,81mmHg (range: 2.7 to 22.1 mmHg) in the control group (P<0,001 ). Corneal resistance factor was 7.59+/- 2,06 mmHg (range: 4.1 to 15.1 mmHg) in the keratoconus group and 10.6 +/- 2,03 mmHg (range: 4.10 to 23.70 mmHg) in the control group (P<0,001). Time duration between « in » and « out » signal peaks was 11.36+/- 0,70 ms (range: 9.9 to 14,5 ms) in the keratoconus group and 10.82+/- 0,51 ms (range: 8.7 to 12.6 ms) in the control group (P<0,001). Conclusion Corneal hysteresis and corneal resistance factor were statistically lower in the keratoconus group compared with the control group as it was already showned in former studies. Time duration between “in” and “out” signal peaks is statistically significantly higher in the keratoconus group. This measure could be used in the evaluation of corneal biomechanical properties.