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K. D. Sejpal, D. Johnson, F. Yu, D. R. Hamilton; Advanced Assessment of Corneal Biomechanical Properties in Normal and Keratoconic Eyes Using the Ocular Response Analyzer. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4991.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate corneal biomechanics in normal and keratoconus subjects by analysis of waveform parameters obtained from the Ocular response analyzer (ORA, Reichert Instruments)
This is a retrospective, comparative case series performed between April 2005 and April 2009. ORA waveform parameters (39) were compared between groups of patient with manifest keratoconus (KCN) and normal corneas, which were age and gender matched. The KCN group included patients with manifest keratoconus based on the Keratoconic Severity Score of 3 or more as defined by the Collaborative Longitudinal Evaluation of Keratoconus Study Group. The signals with the highest waveform score were selected for analysis. The central corneal thickness was measured with an ultrasonic pachymeter.
Seventy-three eyes of 54 keratoconus (KCN) subjects and 115 eyes of 115 normal subjects were included. The mean Corneal Hysteresis (CH) was 8.1+1.5 mm Hg in KCN and 11+1.6 mm Hg in normal eyes (p<0.0001). The mean Corneal Resistance factor (CRF) was 7.5+1.9 mm Hg in KCN and 11.2+1.9 mm Hg in normal eyes (p<0.0001). Thirty-two of the remaining 37 parameters were statistically significantly different in the two groups (p<0.05). The receiver operator characteristic (ROC) curves for individual parameters, revealed an area under the curve of >0.9 for CH, CRF, area under peak 2 (p2area) and down slope of peak 1 (dslope1). Multivariable logistic regression model with stepwise variable selection was performed to identify factors which best distinguish the two groups, after adjusting for age, gender and central corneal thickness. CRF (p=0.010), p2area (p=0.028) and aindex (degree of non-monotonicity of peak 1, p=0.010) were the most differentiating parameters. The area under the curve for this model was 0.991 with a sensitivity of 93.2% and specificity of 97.4%.
Waveform analysis of corneal biomechanical signals can be used to distinguish normal from keratoconic corneas. A model using 3 waveform parameters provided high sensitivity and specificity for separating the two groups. Further studies are required to investigate the utility of these waveform parameters in distinguishing more subtle forms of keratoconus from normal corneas and in monitoring the progression of keratoconus.
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