Handheld Adaptive Optics Scanning Laser Ophthalmoscope for in vivo Imaging of Cone Photoreceptors

Abstract

Purpose : Visualization of individual photoreceptors close to the fovea with the current generation of large footprint tabletop adaptive optics (AO) scanning laser ophthalmoscope (SLO) systems is largely limited to patients that are able to sit upright. We describe a handheld AOSLO (HAOSLO) system that utilizes a light and compact AO framework and custom optics and mechanics to achieve photoreceptor visualization near the fovea with potential applications for neonatal imaging.

Methods : A compact deformable mirror (DM) with 69 actuators and a 10.5 mm pupil diameter was used as the adaptive element to correct for wavefront distortions. The optical system incorporated nine custom achromatic lenses that were designed with a consideration for manufacturability via a tolerance stack analysis in optical design software. The handheld probe, weighing less than 400 grams, permitted a 1.4° x 1.6° field of view and 2.5 µm lateral resolution at a speed of 8.3 frames per second. Optical aberrations were corrected without a wavefront sensor by using a stochastic parallel gradient descent algorithm similar to that of [Porter et al. Opt. Express (2011)] until the mean intensity of the acquired image was maximized. To improve the convergence time, a Zernike polynomial control basis was used instead of the DM’s actuator basis and downsampling was applied to the acquired image during sensorless correction to increase the iteration rate from 8.3 Hz to 41.5 Hz.

Results : The handheld probe design was fabricated, calibrated, and used to acquire retinal images of four undilated, healthy human adult volunteers after dark adaptation. High-resolution retinal images visualizing the photoreceptor mosaic were acquired as close as 1.4° from the fovea (Figure 1).

Conclusions : We have demonstrated the first HAOSLO system and have tested it to achieve photoreceptor visualization near the fovea in four adult volunteers. The use of this technology may provide a compact solution for imaging photoreceptors near the fovea in patients that are supine or under anesthesia and should also be suitable for use with neonates and young children.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Figure 1. a) Photograph of HAOSLO in handheld use. The handheld probe has a form factor of 10.3 x 5.3 x 11.2 cm. b) 1° field of view retinal image (single frame) acquired with the probe after sensorless AO correction on a dark-adapted adult volunteer at a location 1.4° superior to the fovea. Scale bar, 0.25°.