Second-Generation Corneal Deformation Signal Waveform Analysis in Low and High Astigmatism Normal Corneas After Statistical Correction for Potentially Confounding Factors

Zhang, Lijun

Second-Generation Corneal Deformation Signal Waveform Analysis in Low and High Astigmatism Normal Corneas After Statistical Correction for Potentially Confounding Factors

Monday, April 28, 2014: 8:06 AM

Room 155 (Boston Convention and Exhibition Center)

Lijun Zhang, MD, Jules Stein Eye Institute, Los Angeles, CA, USA

D. Rex Hamilton, MD, MS, Jules Stein Eye Institute, Los Angeles, CA, USA

Vivian Phan, OD Los Angeles, CA, USA

Fei Yu, PhD, JSEI, UCLA, Los Angeles, CA, USA

Jennifer N. Danesh, BS los angeles, CA, USA

Narrative Responses:

Purpose
To evaluate and compare the difference in corneal biomechanical waveform parameters between low astigmatism (cylinder < 1.0 D = LA) and high astigmatism (cylinder > 2.5 D = HA) normal corneas with a second generation ocular response analyzer (ORA), after controlling for potentially confounding factors.

Methods
A second generation ORA was used to obtain the corneal hysteresis (CH), corneal resistance factor (CRF), and 37 biomechanical waveform parameters in 200 LA eyes (125 patients) and 22 HA eyes (15 patients). Parameter differences between the two groups were assessed using T tests. A multivariable logistic regression model with stepwise variable selection was used to select the parameters most useful in distinguishing between the two groups, and was adjusted for central corneal thickness (CCT), gender and age to control for potential confounding effects.

Results
After controlling for confounding factors, there was no statistically significant difference between the mean CRF in the LA group (10.0±1.8 mmHg) and the mean CRF in HA group (9.7±1.5 mmHg)(p=0.41). There was no statistically significant difference between the mean CH in the LA group (10.6±1.5 mmHg) and the mean CH in HA group (10.4±1.6 mmHg)(p=0.53). Only one parameter: aspect1(aspect ratio of peak1; p=0.03) was found to be useful in distinguishing between two groups.

Conclusion
There is no difference in biomechanical waveforms between eyes with low and high regular astigmatism. Therefore, differences identified in the waveforms between keratoconic and normal eyes are not based on shape but rather biomechanical differences. This adds to the specificity of the ORA as a diagnostic tool for keratoconus.