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Daniel Tso, Qian Du, Ronald Miller; Imaging stimulus-evoked reflectance changes in human retina. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2307.
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We have previously reported studies imaging the stimulus-evoked changes in near-infrared (NIR) reflectance in the human retina (Abramoff et al 2006). We have subsequently conducted a series of studies using this method in other species that have more precisely characterized the imaged retinal signals and have provided evidence as to their nature and their anatomic origins in the outer retina. The signals originally observed in the human were less robust and required a more intense stimulus than in cat retina. To develop an imaging procedure suitable for routine use in humans, we have worked presently to optimize the imaging protocol and visual stimulus parameters.
Changes of retinal reflectance of NIR light (780-830 nm) were imaged during the presentation of visual stimuli using a modified fundus camera with a digital camera. Stimuli we used including LEDs, laser diodes or laser-generated patterns presented for 300ms. Normal human subjects were examined.
A decrease of retinal reflectance was observed within 500ms after the stimulus, peaking after 1 second, with the magnitude of ~0.5%, gradually returning to baseline in 2-6 seconds. The spatial pattern of the signal corresponded to the visual stimulus in size, location and pattern -- for example, a spot-shaped retinal region 0.8 mm in diameter after a visible laser spot (1000 cd/m2) was presented as the stimulus. The signal had a point spread of less than 500 µm. In another example, a dark bar-shaped region was observed on the retina after a laser-generated bar (1000 cd/m2) was presented. Results were repeatedly observed in the subjects. Signals were visible by analyzing data collected from only one to two trials, which took less than 2 minutes to image.
We have refined our imaging protocols yielding more consistent observations of negative intrinsic signals in the human retina. These signals have spatial specificity and small point spread. Furthermore, these signals were evoked by a relatively low intensity stimulus (compared with most previous studies), and were recorded within a short time. This technique may have potential as a new method for diagnosing and monitoring retinal disorders. In addition, the finding of spatial specificity of the intrinsic signal suggests that in the human retina, the regulation underlying neurovascular coupling is at least as precise as hundreds of microns.
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