Abstract
Purpose :
Corneal scars due to infectious, traumatic, surgical or other origin affect people's vision and therefore the quality of life. Imaging of these pathologies and detecting their location and full extent in detail is complicated and reaches technical limits. Purpose of this study was to assess the exact extent and layer penetration of corneal scars using polarization sensitive OCT (PS-OCT) based on altered birefringent or depolarizing properties of corneal collagen scar tissue.
Methods :
After comprehensive ophthalmic examination of the patients' eyes, images of corneal scars due to trauma, infectious diseases, surgical, hereditary or unknown origin were acquired using anterior segment (AS-) OCT (CASIA 2, Tomey Corporation, Japan). A custom built Swept Source PS-OCT (λ=1045nm, scan time <2sec) was used to generate limbus-to-limbus wide field volume scans of the cornea. For acquisition a raster scan pattern using conical scanning optics design was introduced to compensate for the corneal curvature.
Assessed parameters included corneal layer thickness, area and depth of scarred corneal tissue. Additional polarization-sensitive parameters included localized change of retardation, axis orientation and depolarization.
Results :
20 patients were included in this pilot study. Using PS-OCT, image contrast could be improved compared to the commercially available OCT measurements. While normal stroma shows depolarization of backscattered light, scar tissue shows polarization preserving or birefringent characteristics. Using two orthogonally polarized channels scar morphology could be defined more precisely and more valid detection of epithelium, disintegration and penetration of Bowman's membrane and anterior stromal scaring could be achieved.(Figure 1) The use of the conical scan pattern improved image quality overall without the need of scan averaging.
Conclusions :
AS-PS-OCT with a conical scanning optics significantly improved details on the location, extent and depth of corneal scars. The combined information of intensity data and polarization-sensitive parameters might be beneficial for planning a more individualized treatment of corneal scars using phototherapeutic keratectomy or lamellar keratoplasty.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.