Phase Retardation Mapping Of Different Corneal Thicknesses: A Polarization Sensitive-Optical Coherence Tomography Study
Published 2023 - 41st Congress of the ESCRS
Reference: FP31.08 | Type: Free paper | DOI: 10.82333/hz4e-nm73
Authors: Rahul Prashant Patil* 1 , Raghav Narasimhan 2 , Yash Patel 2 , Rohit Shetty 3 , Pooja Khamar 3 , Christoph Hitzenberger 4 , Michael Pircher 4 , Rudy Nuijts 5 , Abhijit Sinha Roy 2
1IBMS Lab,Narayana Nethralaya Foundation ,Bangalore,India;MHeNs - Neuroscience,Maastricht University,Maastricht,Netherlands, 2IBMS Lab,Narayana Nethralaya Foundation ,Bangalore,India, 3Department of Corneal and Refractive surgery,Narayana Nethralaya Eye Hospital,Bangalore,India, 4Center for Medical Physics and Biomedical Engineering,Medical University of Vienna,Vienna,Austria, 5MHeNs - Neuroscience,Maastricht University,Maastricht,Netherlands
Purpose
To examine the distribution of phase retardation (PR) in healthy corneas and keratoconus (KC) corneas across different thickness groups
Setting
Narayana Nethralaya Eye Hospital, Bangalore, India
Methods
In this retrospective study, 80 corneas were classified into 4 groups based on topography and corneal thickness (CCT): Healthy-1 (CCT<550µm), KC-1 (CCT<500µm); Healthy-2 (thick corneas-CCT>550µm); KC-2 (thick corneas-CCT>520µm). All corneas besides routine clinical examination, were imaged using an ultrahigh resolution (UHR) spectral domain Polarization Sensitive-Optical Coherence Tomography (PS-OCT) system. Conical scanning setup was used to allow for an almost perpendicular beam incidence on the corneal surface and provides uniform signal strength throughout the cornea. PR en face and layer thickness maps were generated using information from the two orthogonal polarization channels of PS-OCT.
Results
The PR enface maps of Healthy-1 corneas showed a preferred arrangement of collagen lamellae, resulting in a quasi-rhombus pattern of PR with least retardation (14±2.1°) at the center and increasing radially towards the periphery. In contrast, KC-1 corneas showed a distortion of this pattern. Interestingly, for thick healthy corneas (healthy-2), distorted pattern with higher PR (38±4.2°) was observed, whereas a quasi-rhombus pattern was seen in KC-2 corneas with a larger low PR (17±3.2°) region. Additionally, both KC groups (KC-1 & KC-2) showed significant thinning of Bowman's layer thickness (BLT) maps at the cone location. The area of low PR in Healthy and Keratoconus corneas was found to be statistically significant (P<0.01).
Conclusions
The preferred arrangement of collagen lamellae in healthy corneas and its distortion in keratoconus corneas suggest that PS-OCT can be used as a potential tool, going beyond conventional topography for early detection and diagnosis of corneas that are truly at risk of ectasia. Significant thinning of BLT at the cone location in KC groups underlines its crucial role in the pathogenesis of this disease, requiring further monitoring. Further investigations are required to explore the clinical implications of these findings and to evaluate the potential of PS-OCT in ectasia risk assessment.