Analysis of Various Modalities for Intraocular Pressure Measurement in Relation to Keratoconus Severity in 246 Eyes of the Homburg Keratoconus Center

Waveform Score Influences the Outcome Metrics of the Ocular Response Analyzer in Patients with Keratoconus and in Healthy Controls

PURPOSE

To test whether the intraocular-pressure (IOP) and biomechanical outcome metrics from the Ocular Response Analyzer (ORA) differ between the measurement with the highest waveform score and the average of four measurements of any waveform score in participants with keratoconus and in controls.

METHODS

Patients with diagnosed keratoconus and healthy controls were recruited prospectively. Four measurements were made using a third-generation ORA. Goldmann-correlated IOP (IOPg), corneal-compensated IOP (IOPcc), corneal hysteresis (CH), corneal resistance factor (CRF), waveform score, and six waveform parameters (p1area, p2area, w1, w2, h1, and h2) were considered as outcome metrics. In the left eye, outcomes from the measurement with the highest waveform score were compared against averaged outcomes from four measurements of any waveform score using either paired t-tests or Wilcoxon signed-rank tests. Receiver operating characteristic (ROC) curves tested ability of both data-selection approaches to differentiate the cohorts.

RESULTS

One-hundred ninety-two (N = 192) participants were enrolled. In the control cohort (n = 145), waveform score, CH, p2area, and h2 were all significantly greater for the best-waveform-score measurement than for the average-waveform-score measurement. IOPcc and w2 were significantly less for the best-waveform-score measurement than for the average-waveform-score measurement. In the keratoconus cohort (n = 47), waveform score, p1area, p2area, h1, and h2 were all significantly greater for the best-waveform-score measurement than for the average-waveform-score measurement. W2 was significantly less for the best-waveform-score measurement than for the average-waveform-score measurement. The area under the ROC curve was high for both data-selection approaches.

CONCLUSION

In general, the best measurement had higher and narrower waveform peaks than the averaged measurement, which suggests better alignment between the device and the eye in the former than in the latter. Thus, making multiple measurements and then analyzing the one with the single highest quality may be preferred to analyzing the average of the group.

Altered Corneal Biomechanics According to the Biomechanical E-Staging in Pellucid Marginal Degeneration

PURPOSE

The purpose of this study was to investigate corneal biomechanics in pellucid marginal degeneration (PMD) compared with healthy controls using Corvis ST (Oculus, Germany) by using the new biomechanical E-staging (based on the Corvis Biomechanical Factor, the linearized Corvis Biomechanical Index) together with tomographic parameters.

METHODS

Corneal biomechanical and topographic data of 75 eyes of 75 patients with PMD and 75 eyes of 75 age-matched and sex-matched healthy controls were investigated. Topographic parameters (K1, K2, Kmax, central corneal thickness (CCT), and Belin/Ambrósio Deviation Index (BAD-D) were evaluated in dependence of and correlated with the biomechanically defined E-stages. Biomechanical parameters were also recorded for the 2 groups.

RESULTS

Patients with PMD showed higher K2, Kmax, BAD-D, and Corvis Biomechanical Factor values and a lower CCT compared with healthy controls ( P < 0.001). The E-stage was positively correlated with K1, K2, Kmax, BAD-D, and intraocular pressure difference and negatively correlated with CCT. Stage-dependent analysis revealed a significant increase in K1, K2, Kmax ( P < 0.001), and BAD-D ( P = 0.041) in stage E3 compared with E0 and a significant decrease in stage E2 in CCT ( P = 0.009) compared with E0.

CONCLUSIONS

This study showed that patients with PMD may have a reduced corneal stiffness compared with healthy controls which worsens with increasing E-stage. Significant changes in topographic parameters were observed at stage E2 for CCT and at stage E3 for K1, K2, Kmax, and BAD-D when compared with stage E0.

Intraocular Pressure Measurements in Standing, Sitting, Prone, and Supine Positions

In this study, intraocular pressure (IOP) was measured in sitting, supine, prone, and standing (ST) positions and again five minutes after standing (ST-5) utilizing a Tono-Pen AVIA in 124 eyes of 62 healthy subjects with ages ranging from 21 to 59 years (mean 30 ± 10 years). In each subject, the average IOP of both eyes was used for the statistical evaluation. The mean IOP difference between the ST and sitting positions was -0.13 ± 1.63 mmHg (p = 0.548); between ST-5 and sitting, it was 0.53 ± 1.24 mmHg (p = 0.001); between supine and sitting, it was 1.30 ± 1.48 mmHg (p < 0.001); between ST and supine, it was -1.43 ± 1.74 mmHg (p < 0.001); between ST-5 and supine, it was -0.77 ± 1.59 mmHg (p < 0.001); between prone and supine, it was 2.24 ± 1.92 mmHg (p < 0.001); between ST and ST-5, it was -0.67 ± 1.84 mmHg (range: -7.5 to 5 mmHg) (p = 0.007); between prone and ST, it was 3.46 ± 2.01 mmHg (p < 0.001); between ST-5 and prone, it was -2.46 ± 1.67 mmHg (p < 0.001); and between sitting and prone, it was -3.22 ± 1.56 mmHg (p < 0.001). The results show a significant IOP increase in the ST-5 position, suggesting that such measurements need to be performed in an attempt to explain the progression of glaucoma in apparently normal-tension patients.

Intraocular pressure measurement and association with corneal biomechanics in patients underwent Descemet's stripping with endothelial keratoplasty: a comparative study

Purpose

To compare corneal biomechanical properties and intraocular pressure (IOP) measurements in patients who underwent Descemet's stripping with endothelial keratoplasty (DSEK) with those of the follow healthy eyes.

Methods

In this retrospective comparative study, a total of 35 eyes of 35 patients who underwent DSEK by a single surgeon from 2015.02 to 2019.12 were enrolled along with their fellow healthy eyes. Corneal biomechanical parameters were assessed at least 3 months post-DSEK using Corneal Visualization Scheimpflug Technology (CST). IOP was measured by CST, Goldmann applanation tonometry (GAT), and MacKay-Marg tonometer.

Results

Central corneal thickness (CCT) and stiffness parameter at first applanation (SP-A1) were significantly increased after DSEK when compared to the fellow eyes. In DSEK eyes, biomechanically-corrected intraocular pressure (bIOP) and MacKay-Marg IOP correlated significantly with GAT IOP measurements, with bIOP showed the lowest IOP values. All the IOP values did not correlate with CCT. However, GAT-IOP and MacKay-Marg IOP showed a positive correlation with SP-A1.

Conclusion

The corneal stiffness increased after DSEK. Central corneal thickness may have less influence than corneal biomechanics on IOP measurements in eyes after DSEK. Biomechanically-corrected IOP obtained by CST seemed to be lower than other tonometry techniques in DSEK eyes, perhaps because of correction for corneal stiffness, CCT and age.