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Sujin Hoshi, Shinichi Fukuda, Masahiro Yamanari, Yiheng Lim, Tetsuro Oshika, Yoshiaki Yasuno; Evaluation Of Birefringence In Eyes With Keratoconus Measured By Polarization-sensitive Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4123.
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The corneal morphological characteristics of eyes with keratoconus have been intensively investigated. However, internal characteristics such as disruption of the lamellar arrangement, which is prodrome to the development of morphological changes were difficult to evaluate. We assume that the birefringence of the cornea may be sensitive to the lamellar arrangement and be different in keratoconus from the normal cornea, which is known to have low birefringence at the central region. In this study, we evaluate the change of birefringence in keratoconus by using a prototype office-based polarization-sensitive optical coherence tomography (PS-OCT).
Nineteen eyes of 19 normal subjects, 8 eyes of 8 subjects with keratoconus suspect, and 28 eyes of 19 patients with keratoconus were scanned by TMS-5, CASIA and PS-OCT at Tsukuba University Hospital. Corneal thickness and regular and irregular astigmatism were obtained by CASIA. Phase retardation tomography which reflects birefringence of the cornea was obtained by high-speed swept-source PS-OCT.
The phase retardations of the central 3-mm diameter were higher in patients with keratoconus compared with normal subjects (p < 0.01). Phase retardations of the corneas with keratoconus, keratoconus suspect, and normal subjects were 0.64 ± 0.53, 0.32 ± 0.15, and 0.24 ± 0.17 radians, respectively. Corneal thicknesses were thinner in the patients with keratoconus. The figures show representative OCT and phase retardation images. In Fig. (a) of the normal cornea, neither hyper-scattering nor strong birefringence were observed. Strong birefringence was found in keratoconus corneas, as shown in Fig. (b).
PS-OCT can noninvasively measure birefringence and detect the disruption of lamellar arrangement in the cornea with keratoconus. The results may imply that PS-OCT has potential in evaluating keratoconus even before its development from the aspect of internal characteristics of the cornea.Fig. B-scan images of the phase retardation (a), (b), en face phase retardation images at the posterior surface (c), (d) and topography images (e), (f) of the corneas without marked anterior disorder and with keratoconus, respectively.
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