Mapping of corneal birefringence in thin and asymmetric keratoconus corneas with ultrahigh resolution polarization sensitive OCT.
J Cataract Refract Surg 2022;
48:929-936. [PMID:
35082233 DOI:
10.1097/j.jcrs.0000000000000898]
[Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Accepted: 01/21/2022] [Indexed: 11/26/2022]
Abstract
PURPOSE
To evaluate phase retardation (PR) across healthy, thin corneas (< 500 µm), asymmetric and bilateral KC.
SETTING
Narayana Nethralaya, Bangalore.
DESIGN
Observational, cross-sectional.
METHODS
There were four eye groups: healthy (group 1; n=10 eyes), thin corneas with no clinical disease (group 2; n=10 eyes), asymmetric KC (group 3; n=5 eyes) and clinical KC (group 4; n=15 eyes). All eyes were imaged with polarization sensitive OCT (PS-OCT), MS-39 and Corvis-ST. Using PS-OCT, the phase retardation (PR) was analysed in annular regions. The anterior (A-E) and Bowman's (E-B) wavefront aberrations, Epithelium Zernike indices (EZI), total corneal thickness, Corvis biomechanical index (CBI), total biomechanical index (TBI) and Belin-Ambrosio overall deviation index (BAD-D) were analysed.
RESULTS
Only the CBI, TBI, BAD-D, the A-E and E-B aberrations, EZI and total corneal thickness distributions of groups 1, 2 and 3 were similar (p>0.05) but not CCT (p<0.05). The PR distributions clearly showed that the eyes in groups 1, 2 and 3 had a normal corneal birefringence unlike group 4 eyes (p<0.05). The PR map was similar to the preferred orientations of collagen fibers seen in X-ray diffraction ex vivo studies of corneal stroma.
CONCLUSION
The PR distributions may eliminate the uncertainty associated with the stromal status of thin and asymmetric KC corneas. The group 2 and 3 eyes appeared as healthy due to normal corneal birefringence at the time of imaging and longitudinal follow-up of these eyes with PS-OCT may assist in early detection of onset of disease.
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