Comparison of Scheimpflug and swept-source anterior segment optical coherence tomography in normal and keratoconus eyes.

Purpose: The purpose of the study was to assess the agreement of anterior segment optical coherence tomography with its older well-known opponent i.e., Sheimpflug imaging in evaluation of the cornea in normal and keratoconus subjects.
Methods: 107 normal and 56 keratoconus eyes were evaluated with the anterior segment optical coherence tomography followed by the Scheimpflug imaging. Parameters included axial keratometry data in both of steep and flat meridians, mean keratometry and the astigmatism values in the central 4.0 mm zone, central, thinnest and apex corneal thicknesses, Q-value in 8 mm zone and pupil diameter. Corneal topographic maps were recorded and were evaluated for anterior highest and lowest points, posterior highest and lowest points. Average values were recorded for analysis.
Results: All anterior cornea keratometry indices showed perfect agreement between two devices in normal corneas; while the level of agreement in keratoconus cases ranged from moderate to strong. All posterior keratometry indices also showed perfect agreement in both groups; except for flat K in normal corneas and steep K in KC ones. The amount of corneal cylinder in normal corneas had perfect agreement, and moderate to strong agreement in anterior/posterior cornea in keratoconus group. Anterior highest and lowest points showed strong and perfect agreement in normal and keratoconus cases, respectively. Posterior highest and lowest points showed strong agreement in normal cases. Thickness indices (central, thinnest, and apex thicknesses) showed perfect agreement between two devices in both normal and KC groups. Mean values of anterior and posterior highest points were statistically higher in Scheimpflug system.
Conclusions: Although two imaging technologies had statistically numerical different output, it seems that they have a good agreement in most parameters.