Intraocular pressure and ocular biomechanical parameters vary between generations of the ocular response analyzer in healthy and ectatic eyes

Abstract

Introduction: This study evaluated the agreement between a third-generation (G3) ocular response analyzer (ORA) and a first-generation (G1) ORA, and tested the ability of the keratoconus match index (KMI) to identify keratoconus.

Methods: Healthy participants (n = 149 eyes) and participants with keratoconus (n = 78 eyes) were enrolled for this study. Four measurements were taken bilaterally using the G1 and G3 ORA. Goldmann-correlated intraocular pressure (IOPg), corneal-compensated IOP (IOPcc), corneal hysteresis (CH), waveform score, KMI, and waveform parameters area under the first applanation peak (p1area), area under the second applanation peak (p2area), width of the first applanation peak (w1), width of the second applanation peak (w2), height of the first applanation peak (h1), and height of the second applanation peak (h2) were recorded from the measurement with the highest waveform score in the left eye. Paired t-tests or Wilcoxon signed-rank tests were used to assess agreement between the devices, and receiver-operating characteristic curves determined the ability of KMI to identify eyes with keratoconus.

Results: There was no difference in IOPcc or IOPg between the devices in both cohorts. CH was significantly greater for the G3 than for the G1 in healthy participants but not in keratoconus participants. For both cohorts, measurements of waveform score, KMI, p1area, p2area, w2, h1, and h2 were greater for the G3 than for the G1. Only w1 was smaller for the G3 than for the G1. There was no difference in the ability of KMI to differentiate ectatic from healthy eyes between the devices.

Discussion: Although the G1 and G3 can identify keratoconus using KMI, there is meaningful variation between them in IOP and biomechanical outcome parameters. Thus, clinicians and researchers should compare results between the devices with caution and should state which generation produced the data.

Keywords: cornea; corneal hysteresis; intraocular pressure; keratoconus; tonometry; waveform parameters.

Figure 1

Agreement between the ocular response analyzer (ORA) G1 and ORA G3 for (A) Goldmann-correlated intraocular pressure (IOPg), (B) corneal-compensated IOP (IOPcc), and (C) corneal hysteresis (CH) in the healthy cohort (n = 149). The center solid blue lines are inter-device mean difference, and the flanking dashed blue lines are the limits of agreement, from 1.96 to −1.96 standard deviations.

Figure 2

Agreement between the ocular response analyzer (ORA) G1 and ORA G3 for (A) Goldmann-correlated intraocular pressure (IOPg), (B) corneal-compensated IOP (IOPcc), and (C) corneal hysteresis (CH) in the keratoconus cohort (n = 78). The center solid blue lines are inter-device mean difference, and the flanking dashed blue lines are the limits of agreement, from 1.96 to −1.96 standard deviations.

Figure 3

Receiver-operating characteristic (ROC) curves representing the ability of the keratoconus match index (KMI) to distinguish the keratoconus participants from the healthy participants using the G1 ocular response analyzer (ORA, black trace) and G3 ORA (red trace). A is area under the ROC curve.