Scheimpflug Imaging Analysis in Forme Fruste Keratoconus, Keratoconus, and High Astigmatism and Myopia: Intereye Asymmetry Study
Purpose
To evaluate the intereye asymmetry of several parameters obtained from Scheimpflug Imaging to discriminate between high myopic and high astigmatism eyes from forme fruste keratoconus (FFKC) and keratoconus.
Methods
This prospective, comparative study included 424 patients (748 eyes), 294 with bilateral keratoconus (KC), 50 with high myopic or astigmatism, and 30 patients with FFKC, and 50 patients with low ametropia as a control group, between July 2012 to July 2014. 30 parameters obtained from Scheimpflug analyzer derived from pachymetry, curvature, anterior and posterior elevation, corneal wavefront, asphericity and others was analyzed. Asymmetry was determinate by subtracting the right eye value from the left eye value for each variable and by considering the absolute value of the result. Receiver operating characteristic curves (ROC) and logistic regression analysis was used.
Results
Mean asphericity asymmetry in KC group was 0.36 um compared with 0.05 in the high ametropic group (p< .001). Mean steep keratometry asymmetry in KC was 2.26D (diopters) compared with 0.48 D in the high ametropic group (p=0.01). Mean anterior elevation (at the apex) asymmetry was 7.34 um compared with 1.61 um in the high ametropic group (p= 0.03). Mean posterior elevation (at the apex) asymmetry was 15.49 um compared with 3.92 um in the high ametropic group (p= 0.05). Asphericity had an area under the ROC of 0.97 discriminating between KC and high ametropic eyes.
Conclusion
There is a greater intereye asymmetry in eyes with keratoconus compared with eyes with high myopic or astigmatism. Asymmetry values between eyes in ashpericity, curvature and elevation parameters showed to be effective discriminating between keratoconus and high ametropic eyes.