Rods and cones imaged with a commercial adaptive optics scanning light ophthalmoscope (AOSLO) prototype

Abstract

Purpose: Our goal is to develop a commercial adaptive optics scanning light ophthalmoscope (AOSLO) that is compact, easy to use, and has comparable resolution to existing research AOSLOs. We previously demonstrated a prototype commercial AOSLO capable of axial sectioning and high resolution imaging across a large dioptric range using dual liquid crystal on silicon spatial light modulators (LCOS-SLMs) for wavefront correction. Here we present modifications to our system to increase resolution and improve image quality.

Methods: The AOSLO was improved by: 1) increasing the maximum pupil size at the eye to 6.7 mm, thus providing 3 µm theoretical lateral resolution at 840 nm, 2) using the same light source for both imaging and wavefront sensing, 3) optimally arranging the LCOS-SLMs to modulate the phase of each polarization component independently and minimize the undesired effects of diffracted light and 4) implementing real-time closed-loop wavefront correction. Real-time software tracking of pupil size and position ensured correction stability. The relatively compact optical system (28”×18”) uses a focusing lens to achieve a high dioptric range (-10D to +5D). We imaged 9 healthy human eyes at 0°, 1.7° and 3.5° on both the modified system and an original system to compare performance. 2 subjects were also imaged at 7° in the modified system only. Cones were identified by an experienced grader masked to the system of origin using a semi-automated method and computed nearest neighbor distance (NND).

Results: It was difficult to determine the precise eccentricity at which cones became visible, as we did not sample continuously from the foveal center outwards. However, cones were visible in the images obtained at 0° fixation in 7/9 subjects in the modified system; for these eyes the mean eccentricity beyond which cones were visible was 0.41° (range:0.17°-0.60°). The mean of the 100 cones with the lowest NND for these eyes was 0.45 arcmin. In the original system, cones were not visible until some eccentricity >0.83°. Rods could be seen in the modified system in some images at ~7°.

Conclusions: This work demonstrates the suitability of LCOS-SLMs for wavefront correction in a commercial AOSLO device. We successfully imaged both rods and foveal cones in some subjects by substantially improving the performance of our AOSLO system, which is now approaching the resolution of the best research-grade AOSLOs.

Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)