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P. A. Bedggood, P. R. Martin, U. Grunert, A. Metha; Marmoset Cone Photoreceptor Imaging Using a Compact Adaptive Optics Ophthalmoscope. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2323.
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© ARVO (1962-2015); The Authors (2016-present)
To enhance electrophysiological and anatomical studies of retinal and central pathways serving color vision, we undertook to image the cone photoreceptor mosaic of a common marmoset (Callithrix jacchus) during routine electrophysiology-recording experiments.
We designed and built a compact Adaptive Optics (AO) flood-illuminated ophthalmoscope. The instrument is portable (16.7 kg) and can be transported and attached to an electrophysiology-recording rig. The instrument is optimized for imaging marmoset eyes, with wide field of view (5.2° in diameter) projecting onto a non-cooled 2048 x 2048 pixel CCD camera (Megaplus ES4020). Shack-Hartmann aberrometry drives a pupil-conjugate Mirao 52d deformable mirror to correct wavefront error over a 3.2 mm dilated pupil (tropicamide 0.5%). Retinal images from one anaesthetized marmoset were collected at 15 Hz, using 5 ms pulses of light delivered via 400 m of 400 µm optical fiber from a 671 nm multimode diode laser. At the end of the experiment, the animal was overdosed with sodium pentobarbitone then perfused with 4% paraformaldehyde in 0.1M phosphate buffer for 10 min. Eyes were removed, cut open and immersion fixed in the same solution for 20 or 30 min. Retinas were dissected and prepared as whole-mounts.
Adaptive optics corrected image quality was sufficient to resolve cone photoreceptors across the horizontal meridian from 13° temporal to 16° nasal retina, including the optic nerve head. Recovered cone density profiles over the measured field are in agreement with established figures from histological data, peaking at 120,000 cones/square mm within 0.5 mm of the fovea and declining to 40,000 cones/square mm at 13° eccentricity.
Cone-resolved retinal imaging using a portable AO ophthalmoscope is a viable adjunct to electrophysiological and anatomical investigations of color vision.
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