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Yiheng Lim, Masahiro Yamanari, Shinichi Fukuda, Tetsuro Oshika, Yoshiaki Yasuno; Abnormal Birefringence Of Keratoconus Measured By Polarization-sensitive Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5279.
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© ARVO (1962-2015); The Authors (2016-present)
The central region of healthy cornea is known to have low birefringence compared to peripheral regions, because birefringence of the orthogonal fibrils in successive lamellae cancels each other. By investigating the change of birefringence, disruption of the lamellar arrangement in the cornea of keratoconus could be observed. The purpose of this paper is to demonstrate the visualization of abnormal birefringence in keratoconus by using a prototype office-based polarization-sensitive optical coherence tomography (PS-OCT).
10 corneas of 5 subjects without marked anterior disorder and 29 corneas of 17 subjects diagnosed with keratoconus were scanned by PS-OCT that was developed in Univ. of Tsukuba. This PS-OCT uses 1.3 um probing wavelength and possesses a depth resolution of 9.7 um. This device is based on swept-source OCT technology, and hence the high-speed scan (30,000 A-lines/s) and volumetric scan are available. A conventional structural OCT and phase retardation tomography which reflects the birefringence of the sample were obtained simultaneously within 2.6 s as volumetric tomographies consisting of 512 times 128 A-lines.
The figures show representative scattering and phase retardation tomographies. In the normal cornea (Figs. (a) and (b)), no hyper-scattering and strong birefringence were observed. It was consistent in all 10 eyes. Strong birefringence was found in 6 of 29 keratoconus corneas, as shown in Fig. (d). In these 6 corneas, strong birefringence appears not beneath but in area aside from the thinnest region. Evidence of non-uniform strong birefringence pattern was observed in the en face phase retardation map as indicated by an arrow in Fig. (f).
Three-dimensional distribution of birefringence in keratoconus was observed using PS-OCT. The results may imply that PS-OCT has potential to visualize the disruption of lamellar arrangement in the cornea. This further suggests the possibility of application of PS-OCT to very early keratoconus detection before structural deformation.
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