Adaptive optics imaging of the human retina

Abstract

Adaptive Optics (AO) retinal imaging has provided revolutionary tools to scientists and clinicians for studying retinal structure and function in the living eye. From animal models to clinical patients, AO imaging is changing the way scientists are approaching the study of the retina. By providing cellular and subcellular details without the need for histology, it is now possible to perform large scale studies as well as to understand how an individual retina changes over time. Because AO retinal imaging is non-invasive and when performed with near-IR wavelengths both safe and easily tolerated by patients, it holds promise for being incorporated into clinical trials providing cell specific approaches to monitoring diseases and therapeutic interventions. AO is being used to enhance the ability of OCT, fluorescence imaging, and reflectance imaging. By incorporating imaging that is sensitive to differences in the scattering properties of retinal tissue, it is especially sensitive to disease, which can drastically impact retinal tissue properties. This review examines human AO retinal imaging with a concentration on the use of the Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO). It first covers the background and the overall approaches to human AO retinal imaging, and the technology involved, and then concentrates on using AO retinal imaging to study the structure and function of the retina.

Cones in ageing and harsh environments: the neural economy hypothesis

“…Again, image contrast is improved when using laser scanning and confocal apertures. However, for the highest density cones and many other structures, only by correcting aberrations across the pupil can the contrast improve sufficiently to visualise small or subtle structures . For instance, normal retinal capillaries could finally be visualised without the addition of a contrast agent such as sodium fluorescein, when using a phase plate at the pupil plane to correct aberrations in a SLO instrument .…”

“…For instance, normal retinal capillaries could finally be visualised without the addition of a contrast agent such as sodium fluorescein, when using a phase plate at the pupil plane to correct aberrations in a SLO instrument . A variety of methods are now used for computing and/or measuring wavefront aberrations and compensating for these aberrations, frequently in real time by using adaptive optics (AO), such as a deformable mirror, and are reviewed in detail . The resulting instrument is an adaptive optics scanning laser ophthalmoscope (AOSLO), although AO instruments using flood illumination can provide high speed imaging, but at the cost of contrast .…”

“…A variety of functional measurements is possible on a microscopic scale using AO, with the potential to map the location of the stimuli with respect to the retina, also reviewed in detail . As with the wider field stimuli, there are two main types of methods for functional measurements.…”

Adaptive optics imaging of the retinal microvasculature

“…An aperture blocks light from scattering interactions outside the plane of interest, improving axial resolution and minimising veiling glare. Manipulation of the aperture can reject directly returned light so that the signal only shows scatter from multiple structures; such scatter requires a change in refractive index, rendering otherwise transparent objects . The chief limitation of confocal scanning is the lower frame rate as time is required to form the image; however, scanning can be ‘frozen’ on a cross‐section of a single vessel to afford extremely rapid serial reconstruction of flow …”

“…The magnitude of response and location of any deficits should ideally be co‐localised with the presence and morphology of these important cells. This now appears to be possible with both mural cells and glial cell end‐feet visualised by appropriate manipulation of AOSLO detection geometry . Pericytes in particular could represent a very sensitive biomarker for diabetes due to their central role in pathophysiology of vascular changes in that condition.…”