Noninvasive corneal imaging is essential for the diagnosis and treatment control of various diseases affecting the anterior segment of the eye. This study presents an ultrahigh resolution polarization sensitive optical coherence tomography instrument operating in the 840 nm wavelength band that incorporates a conical scanning design for large field of view imaging of the cornea. As the conical scanning introduces a dispersion mismatch depending on the scanning angle, this study implemented variable, location dependent, numerical dispersion compensation in order to achieve high axial resolution throughout the imaged volume. The corneal images were recorded in vivo in healthy volunteers showing various details of corneal structures.
The phase retardation across healthy and thin corneas (no clinical disease) and asymmetric and bilateral keratoconus clearly showed distinct structural differences not observed in conventional tomography.
Design: Observational.Methods: In this study, all eyes were imaged using a custom-built ultrahigh-resolution PS-OCT and high-resolution hybrid OCT (MS-39). The repeatability of phase retardation en face maps and corneal sublayer thickness profiles was evaluated. The reflectivity and phase retardation were calculated from the 2 orthogonal polarization channels to generate en face maps of phase retardation and corneal sublayer thicknesses. 3 consecutive measurements of all participants were acquired for each eye. For each measurement, the participant was asked to sit back and was realigned again. The repeatability was assessed using the intraclass correlation coefficient (ICC).
Results:The study included 20 healthy eyes of 20 participants.The phase retardation en face maps showed preferential arrangement of collagen fibrils with least retardation in the apex and maximum retardation in the periphery. The phase retardation showed excellent repeatability (ICC >0.95) in all zones. The Bowman layer and stromal layer thicknesses were measured with excellent repeatability (ICC >0.93 and >0.99, respectively). Significant differences (P < .05) in stromal layer thickness were observed between MS-39 and PS-OCT. The repeatability of epithelial thickness measurements was better with PS-OCT than MS-39.
Conclusions:The combinational assessment of corneal birefringence and sublayer thicknesses shows the advanced potential of ultrahigh-resolution PS-OCT in routine clinical practice over current OCT devices.
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