The precision and agreement of corneal thickness and keratometry measurements with SS-OCT versus Scheimpflug imaging

Abstract

Purpose: To assess the repeatability and reproducibility of swept-source optical coherence tomography (SS-OCT) and Scheimpflug system and evaluate the agreement between the two systems in measuring multiple corneal regions in children. Methods: Pachymetric and keratometric maps for both systems were evaluated. Central, midperipheral and peripheral corneal thickness (CT), keratometry and astigmatism power vectors were recorded. The three outcomes yielded by the same observer were used to assess intraobserver repeatability. The differences in the mean values provided by each observer were used to evaluate interobserver reproducibility. Within-subject standard deviation, test-retest repeatability (TRT) and coefficient of variation (CoV) were used to analyze the intraobserver repeatability and interobserver reproducibility. Paired T-test and Bland-Altman were used to appraise interdevice agreement. Results: Seventy-eight eyes of 78 children were included. The CoV was ≤2.12 and 1.10%, respectively, for repeatability and reproducibility. TRT and CoV were lower for central and paracentral CT measurements than for peripheral measurements. The SS-OCT device generated higher precision when acquiring CT data, whereas Scheimpflug system showed higher reliability when measuring corneal keratometry. Although the CT readings measured using SS-OCT were significantly thinner than Scheimpflug device (P < 0.001), the central and thinnest CT values were still of high agreement. The interdevice agreement of keratometry measurement was high for the central corneal region and moderate for the paracentral and peripheral areas. Conclusions: The precision of CT measurements by SS-OCT was higher, while the reliability of keratometry measurements by the Scheimpflug system was higher in children. Apart from the measured values in the central corneal region, the thickness and keratometry readings should not be considered interchangeable between the two systems.

Comparison of corneal thickness measurements using ultrasound pachymetry, noncontact tonopachy, Pentacam HR, and Fourier-domain OCT

“…Two recent reports compared corneal thicknesses obtained with swept-source optical coherence tomography (CASIA SS-1000; Tomey, Nagoya, Japan or CASIA2; Tomey, Nagoya, Japan) and Pentacam. [ 31 , 32 ] Both reports found that Pentacam CCT measurements were thicker than SS-OCT (swept-source optical coherence tomography), by 4.91 and 9.64 μm, respectively. Zhao et al insisted that SS-OCT outperformed the Scheimpflug-based corneal topographic map in measuring corneal thickness.…”

“…The coefficients of variation for corneal thickness measurements were smaller with CASIA SS-1000 than with Pentacam HR. [ 31 ] Li et al emphasized that SS-OCT has the advantage of shorter scanning time and utilizing an infrared light source to minimize the effects of instrument light on pupil movement. [ 32 ]…”

Anterior Ocular Biometrics Using Placido-scanning-slit System, Rotating Scheimpflug Tomography, and Swept-source Optical Coherence Tomography

“…The Scheimpflug camera rotates with the visual axis to take 25 or 50 cross-sectional pictures of the anterior segment. The device calculates a three-dimensional model of the anterior segment from up to 138,000 elevation points, providing information about the anterior and posterior surfaces of the cornea and ACD from the endothelium to the crystalline lens [ 24 ].…”

“…The “Corneal Map,” a scan protocol designed to measure corneal thickness and topography, consists of 16 radial B-scans with evenly spaced angular intervals. The collected information was then processed to create a topographic map of the anterior segment [ 24 ].…”

The progress in corneal translational medicine

“…This includes the option to determine the central corneal thickness. 100 A research group also used anterior segment optical coherence tomography (AS-OCT) and investigated the epithelial thickness (ET) of the central cornea and limbal regions in patients with limbal stem cell deficiency (LSCD) as a diagnostic and staging parameter. 101…”