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Kenneth Matthew McKay, Zachary Harvey, Grace K Han, Alfredo Dubra, Jessica Ijams Wolfing Morgan; Stimulus-evoked optical response of individual cone photoreceptors observed with adaptive optics scanning light ophthalmoscopy. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4944.
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© ARVO (1962-2015); The Authors (2016-present)
In vivo functional assessment of the retina at the cellular level remains elusive and is increasingly important as therapies for blinding conditions are developed. Though the physiology is largely unknown, stimulus-evoked intrinsic signals have potential to assess photoreceptor function. Here, we describe a stimulus-evoked optical response, visible at the cellular level.
Neither dark adapted nor bleached parafoveal cones in 3 normal controls (2 females, ages 34 and 24 and 1 male, age 27) were imaged using a custom adaptive optics scanning light ophthalmoscope. A one-degree square field was illuminated with 8.3μW of 848nm for wavefront sensing, 75μW of 795nm Δ15nm for reflectance imaging, and a background of 344.7nW at 675nm. Half of the field was stimulated with 17.4μW of 675nm for 2s. Images were acquired at 16Hz for 5s before, during, and 20s after stimulation. Intensities of stimulated cones in the 795nm image were normalized by the average intensity of non-stimulated cones in the same image. The change in intensity ratio over time was calculated by subtracting the average pre-stimulus intensity ratio from the intensity ratio for each stimulated cone in each frame. Then, for each image, the standard deviation of the change in intensity ratios over all stimulated cones was calculated to describe the global reflectance variability across the stimulated cones.
We observed a stimulus-evoked response in approximately just under half of cones in the stimulated field of all 3 subjects. Following the stimulus onset, the cone intensity ratio either oscillated between bright and dim, increased, decreased, or remained unchanged. While an individual cone’s change in intensity ratio pattern was not repeatable, each trial did produce a response. On average, the reflectance variability metric reliably increased 229ms (188, 250, 250ms) post-stimulus onset. Non-stimulated cones did not show a response.
We describe a cellular-level near infrared optical response to visible red light stimulation, possibly showing L cone function. Future studies will correlate this optical response to physiological function and examine the response in conditions where photoreceptor function is compromised.
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