Wide Field Retinal Imaging By Adaptive Optics Scanning Laser Ophthalmoscope

Abstract

 

Purpose:

 

The area over which an adaptive optics system can be operated in the diffraction-limit, the so called isoplanatic patch, is sized to approximately 1.5 degree. This size of the isoplanatic patch limits the imaging area of an adaptive optics scanning laser ophthalmoscope (AO-SLO). This study aims at widening the field of view (FOV) of our AO-SLO without loss of lateral resolution by using a customized scanning protocol and successive signal processing.

 

Methods:

 

6 eyes of 3 normal subjects were scanned by a custom-made AO-SLO. The AO-SLO measures the aberrations of the eye by a Shack-Hartmann wavefront sensor (HASO32, Imagine Eyes) with a 840 nm beacon beam and dynamically cancels the aberration by a magnetic deformable mirror (Mirao52, Imagine Eyes). As the aberrations of the eye were canceled, ultra-high-resolution retinal images were acquired by an SLO scanner with a probe beam of 1.04 um wavelength. Wide field scanning was performed by changing the position of the imaging area sequentially. Each retinal patch corresponds to 1.49 degrees by 1.86 degrees FOV and the wide field scanning size corresponds to 1.84 degrees by 4.5 degrees. Acquired AO-SLO images were automatically aligned to generate a wide FOV montage using a phase correlation based image registration algorithm.

 

Results:

 

Photoreceptor cells were clearly observed with a field of view of 1.43 +/- 0.3 degrees by 2.9 +/- 0.2 degrees in 3 of 6 eyes, as shown in Figs. 1. In other measurement sessions we failed to obtain high-resolution retinal images because of vignetting, insufficient AO performance, or improper optical alignment.

 

Conclusions:

 

Photoreceptors were clearly observed within the new wide FOV. The AO closed loop was operated over the entire FOV, however, the residual field aberrations caused a degradation of the image quality at the edge of these images. This can be overcome with further improvements of AO performance.  

 

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