Corneal Topography Using Placido Dual Rotating Scheimpflug, Swept-Source Optical Coherence Tomography, and Placido Scanning-Slit System
Narrative Responses:
Purpose
To compare and evaluate agreement of corneal curvature, thickness and elevation using placido-dual rotating scheimpflug, swept-source optical coherence(OCT) and placido-slit scanning system in normal and post-refractive surgery eyes.
Methods
Corneal topography were measured with placido-dual rotating sheimpflug system(Gallilei, Zeimer Ophthalmic Systems), swept-source OCT system(Casia SS-1000, Tomey) and placido-slit scanning system(Orbscan II, Bausch & Lomb). Patients were divided into 2 groups according to history of myopic refractive surgery. Anterior and posterior keratometry, pachymetry, best-fit sphere radius and posterior elevation were compared and intraclass correlation coefficient(ICC) were calculated among 3 instruments. Ultrasound pachymetry was used as the reference for corneal thickness measurement.
Results
Fifty-nine patients (61 normal eyes, 57 post refractive surgery eyes) were assessed. Repeatability of all instruments were high (ICC >0.95). Although there were statistically significant difference, agreement among 3 instruments was high for anterior keratometry, best-fit sphere radius and pachymetry. Posterior keratometry was agreeable between placido-dual rotating scheimpflug and swept-source OCT system, but placido-slit scanning system was much steeper and not agreeable. Posterior elevation was not agreeable and highest in placido-slit scanning system, lowest in placido-dual rotating scheimpflug system.
Conclusion
Three instruments with different system of topography were agreeable in anterior keratometry and pachymetry. Placido-slit scanning system showed discrepancies in posterior keratometry. The different systems reported much different measurements of posterior elevation of cornea. Our result will be useful in applying these instruments to evaluate accurate state of cornea.