High-resolution in vivo Imaging of the Cat Retina Using Adaptive Optics

Abstract

Purpose: : To image the cat retina with cellular resolution using an adaptive optics (AO) flood illumination fundus camera (FIFC) designed for the human eye.

Methods: : We recorded high-resolution images in 3 eyes of two sedated (medetomidine, 0.1 mg/kg) cats. Ocular wavefront aberrations (OWAs) were corrected using an AO system operating in closed-loop at 10 Hz, based on a 52-actuator electromagnetic deformable mirror and a 1024 lenslet Shack-Hartmann sensor (both Imagine Eyes, France). A square 3°x3° area at the eye fundus was flood-illuminated by a pulsed LED emitting at 850 nm and imaged onto a low-noised CCD camera (Roper Scientific, USA). The animals' pupils were dilated (1% tropicamide) and the effective pupil size was set to 7.5 mm by the instrument. Conjunctival atraumatic clips were used to prevent eyeball movements and eyelids closure. The cornea was artificially hydrated throughout the experiments. To avoid image saturation, we set the exposure time to 1/3 of the time needed with human eyes. Every acquisition consisted in 20 consecutive images, out of which 10 were numerically averaged to produce an enhanced final image.

Results: : The total amount of OWAs was strongly reduced by the AO correction, from 2 to 0.2 microns RMS on average. The resulting images allowed us to visualize retinal cells as well as small blood vessels. Cones and nerve fiber bundles were clearly discernible and their counting was possible. Blood vessels walls were more sharply resolved than in conventional fundus images.

Conclusions: : Retinal imaging with cellular resolution was feasible in cats under sedation using an AO-FIFC designed for human eyes without any optical modification. The system's resolution might be furhter enhanced by optimizing its optical magnification for the cat's pupil size. The AO-FIFC technology could find new applications in clinical, pharmacological and toxicological investigations.

Keywords: retina • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • imaging/image analysis: clinical