A rapid line-scan ophthalmoscope for intrinsic optical signal imaging of retinal photoreceptors Xincheng Yao, Qiuxiang Zhang, and Rongwen Lu Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham AL 35294
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Abstract: The purpose of this study was to validate intrinsic optical signal (IOS) mapping of localized retinal dysfunctions. A rapid line-scan confocal ophthalmoscope was constructed to achieve in vivo IOS imaging at cellular and millisecond resolution. A dynamic spatiotemporal filtering was developed to reject signal contamination of hemodynamic changes on fast IOS recording. Comparative IOS and electroretinography (ERG) recordings revealed a close correlation between the confocal-IOS and retinal ERG, particularly the ERG a-wave. IOS identification of localized (30 µm) retinal dysfunction was validated using laser-injured frog eyes. OCIS codes: 170.2655, 330.4270.
It is well established that many eye diseases, including different forms of retinitis pigmentosa (RP) and age-related macular degeneration (AMD), can produce pathological changes in retinal photoreceptors and their support system. To prevent or slow the progress of vision loss associated with outer retinal disease, early detection and reliable assessment of medical interventions are key elements. Adaptive optics (AO) imaging and optical coherence tomography (OCT) has enabled retinal examination at cellular resolution. However, disease-associated morphological and functional changes, if independently measured, are not always correlated directly in time course and spatial location [1]. Therefore, a combined assessment of retinal function and structure is essential. Stimulus-evoked fast intrinsic optical signals (IOSs) promise an alternative to electroretinography (ERG) for functional measurement of retinal physiology [2, 3]. Because functional IOS images are constructed through spatiotemporal processing of preand post-stimulus images, concurrent structural and functional measurements can be naturally achieved using a single optical instrument. However, the IOS source and mechanism are not well Figure 1. Comparative IOS and ERG analysis. IOS (A) established, and in vivo recording of fast IOSs that have time and ERG (B) were recorded from the same groups of frogs. Each tracing represents an average of four courses comparable to electrophysiological kinetics is challenging. responses evoked by light flashes of progressively We recently developed a line-scan confocal imager to achieve brighter intensities over 5.0 log units (log I/Imax) as in vivo IOS imaging at high-spatial (µm) and high-temporal (ms) indicated by the legend. (C) Normalized magnitude and resolution. Comparative IOS and ERG experiments revealed a (D) time to peak of ERG a-wave, b-wave, and confocal IOS plotted as a function of stimulus strength. close correlation between the confocal-IOS and retinal ERG, particularly the ERG a-wave which has been widely used to evaluate photoreceptor function (Fig. 1). IOS imaging of laserinjured frog eyes indicated that the confocal-IOS could unambiguously detect localized (30 µm) functional lesions in the retina before a morphological abnormality is detectable (Fig. 2). We anticipate that confocal IOS imaging can provide applications in early detection of age-related macular degeneration, retinitis Figure 2. Confocal-IOS images of retinal morphology pigmentosa, and other retinal diseases that can cause pathological (left) and function (right). changes in the photoreceptors. Reference: 1. 2. 3.
Falsini, B., et al., Structure-function relationship in ocular hypertension and glaucoma: interindividual and interocular analysis by OCT and pattern ERG. Graefes Arch Clin Exp Ophthalmol, 2008. Yao, X.C. and Y.B. Zhao, Optical dissection of stimulus-evoked retinal activation. Opt Express, 2008. 16(17): p. 12446-59. Li, Y.G., et al., High spatiotemporal resolution imaging of fast intrinsic optical signals activated by retinal flicker stimulation. Opt Express, 2010. 18(7): p. 7210-7218
