Visualization of Retinal Microstructures by Adaptive Optics Scanning Laser Ophthalmoscope With One-Micrometer Probe

Abstract

 

Purpose:

 

Adaptive optics (AO) is known to provide high-resolution image of in vivo human retina with the resolution around a few micrometers. AO retinal imaging systems with several wavelength probe light up to 915 nm have been demonstrated, and it was found that the retinal microstructure possesses different contrast with different probe wavelength. This study aims at demonstrating AO scanning laser ophthalmoscope (SLO) with further longer wavelength of one micrometer for the visualization of retinal micro structures.

 

Methods:

 

3 eyes of 3 normal subjects examined by AO-SLO with 1 um probe. The AO-SLO is capable of dynamic aberration correction by using an AO subsystem consisting of a 840 nm beacon, a magnetic deformable mirror (Mirao52), and a Shack-Hartmann wavefront sensor. The AO operates at 12 Hz closed loop, and reduces the residual root-mean-squared aberration to less than 0.1 um. The depth of focus was 77 um. In addition to the AO, large stroke defocus was corrected by a Badal optometer. The SLO subsystem uses ASE light source with 1.04 um center wavelength for imaging. The optical power on the cornea was 1.1 mW. The eyes were scanned with a 1 degree by 1 degree field of view at the eccentricity of 7degree. The retinal images were qualitatively accessed by two observers.

 

Results:

 

Clear photoreceptor mosaic was observed for 3 of the 3 eyes, where the depth position of the focus (DPF) was aligned to be close to the photoreceptor layer (figure (a)). When the DPF is set to a nerve fiber layer (NFL), several darks spots were observed with 2 of the 3 eyes (arrow heads in figure (b)).

 

Conclusions:

 

The visibility of photoreceptors of this 1um AO-SLO was comparable to that reported by AO-SLO with shorter wavelength. The dark spots on the NFL were rarely reported by short wavelength AO systems. This may be contrasted specifically by the long 1um wavelength.  

 

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • photoreceptors • optical properties