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A. R. Tumlinson, B. Hermann, B. Povazay, T. H. Margrain, A. Binns, B. Hofer, W. Drexler; In vivo Optophysiology: Depth Resolved Measurement of Intrinsic Optical Signals in Human Retina by Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2001.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the feasibility of functional optical coherence tomography (fOCT) for non-invasive depth resolved optical mapping of the physiological response of the human retina to light stimulus in vivo and to compare the outcome with reported retinal intrinsic optical signals (IOS).
Spatially encoded frequency domain OCT at 1050 nm for high speed (up to 47000 A-scans per second) high resolution retinal imaging has been interfaced to an ophthalmic OCT system equipped with a head rest and a bite bar, visible light stimulus, and readied for simultaneous ERG measurements. The time resolution of the OCT system is about 20 µs. After dark adaptation the dilated eyes were stimulated with a white light pattern stimulus of varying time, intensity and spatial pattern. Reflectivity profiles were recorded with OCT volume scans, partly overlapping with the stimulated area. The examined volume was 10ºx1.6º at different locations; ~15º (rod dominant) and ~1º (cone dominant). Measurements were taken on different time scales, directly after the stimulus to examine fast changes on a ms scale, as well as on a minute scale over 30 minutes to account for slow changes. To reduce the influence of eye motions and physiological noise dedicated post processing techniques for signal extraction have been evaluated.
Non-contact, optical probing of retinal physiological response with ~7 µm axial and ~20 µm transversal resolution to visual stimulation was demonstrated in vivo in normal healthy eyes using functional ultrahigh resolution optical coherence tomography. Our results describe the relationship between electrophysiological and optophysiological responses in humans. Possible explanation of the detected optophysiological signals in the photoreceptors includes hyperpolarisation or altered metabolic rates that cause changes in the mitochondrial refractive index.
Optophysiology, a functional extension of ultrahigh resolution OCT has been extended from ex vivo preparations to living humans. Progress has been made in instrument design, experimental protocol, and signal processing that has the potential to establish this technique as an optical analogue to electrophysiology, by detecting depth resolved variations in optical backscattering caused by physiological tissue changes.
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