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W. Gao, B. Cense, Y. Zhang, R. S. Jonnal, D. T. Miller; Measurement of the Stiles-Crawford Effect Using Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3849.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the contributions of different retinal layers to the Stiles-Crawford effect by using spectral-domain optical coherence tomography (SD-OCT) .
Images were obtained with a fiber-based SD-OCT system with an axial resolution of 6 µm and an A-scan rate of 5 KHz. The illumination source was a broadband superluminescent diode ( = 843 nm, Δ = 50 nm). One eye from each of four subjects was studied with pupil dilated using 1% tropicamide and 2.5% phenylephrine. Illumination and imaging of the retina were realized through the same 2 mm circular aperture that was systematically translated across the subject’s pupil. The optical Stiles-Crawford effect was measured as a function of retinal depth and fit to a Gaussian,10-ρr2, where the directionality, ρ, is in units of inverse square millimeters.
Reflections from the photoreceptor inner/outer segment junctions (IS/OS) and near the posterior tip of the outer segments (POS) were found highly sensitive to the aperture position in the pupil. Reflections from the retinal pigment epithelium (RPE) were largely insensitive. Average ρ values (at 2 degree eccentricity) for the IS/OS, POS, and RPE for the four subjects were 0.06, 0.13, and 0.008 respectively. The ρ value for the IS/OS approached typical psychophysical SCE measurements, while that for the POS approached conventional optical SCE measurements.
Advances in retinal imaging with optical coherence tomography have allowed the first opportunity to axially resolve reflections from within the thick retina and to directly investigate the origin of the optical SCE. The factor of two difference in directionality of the IS/OS and POS reflections suggests different waveguiding properties of the inner and outer segments, or different reflective properties of the two reflecting interfaces.
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