Cellular-resolution in vivo imaging of the feline retina using adaptive optics: preliminary results

To perform cellular-level in vivo imaging of the feline retina using an adaptive optics flood illumination fundus camera (AO FIFC) designed for the human eye.

Cellular-level images were obtained from three eyes of two normal sedated cats. Ocular aberrations were corrected using an AO system based on a 52-acuator electromagnetic deformable mirror and a 1024 lenslet Hartmann-Shack sensor (both Imagine Eyes, Orsay, France). A square 3°×3° area of the ocular fundus was flood-illuminated by a pulsed LED emitting at 850 nm and imaged onto a low-noise, high-resolution CCD camera. The animal's pupils were dilated and the effective pupil size was set to 7.5 mm. Conjunctival atraumatic clips were used to avoid eyeball movements and eyelid closure. The cornea was artificially hydrated throughout the experiments. Each acquisition consisted of 20 consecutive images, out of which 10 were numerically averaged to produce an enhanced final image.

The total amount of ocular aberrations was greatly reduced by the AO correction, from 2.4 to 0.21 microns root mean square on average. The resulting images presented white dots distributed at a density similar to that of cone photoreceptors and they allowed us to visualize small blood vessels and nerve fiber bundles at a higher resolution than classically obtained with conventional fundus photography.

Retinal imaging with cellular resolution was feasible in cats under sedation using an AO FIFC designed for human eyes without any optical modification. The AO FIFC technology could find new applications in clinical, pharmacological, and toxicological investigations.