Confocal Retinal Imaging Using a Digital Light Projector with a Near Infrared VCSEL Source

Cones in ageing and harsh environments: the neural economy hypothesis

PURPOSE

Cones are at great risk in a wide variety of retinal diseases, especially when there is a harsh microenvironment and retinal pigment epithelium is damaged. We provide established and new methods for assessing cones and retinal pigment epithelium, together with new results. We investigated conditions under which cones can be imaged and could guide light, despite the proximity of less than ideal retinal pigment epithelium.

RECENT FINDINGS

We used a variety of imaging methods to detect and localise damage to the retinal pigment epithelium. As age-related macular degeneration is a particularly widespread disease, we imaged clinical hallmarks: drusen and hyperpigmentation. Using near infrared light provided improved imaging of the deeper fundus layers. We compared confocal and multiply scattered light images, using both the variation of detection apertures and polarisation analysis. We used optical coherence tomography to examine distances between structures and thickness of retinal layers, as well as identifying damage to the retinal pigment epithelium. We counted cones using adaptive optics scanning laser ophthalmoscopy. We compared the results of five subjects with geographic atrophy to data from a previous normative ageing study. Using near infrared imaging and layer analysis of optical coherence tomography, the widespread aspect of drusen became evident. Both multiply scattered light imaging and analysis of the volume in the retinal pigment epithelial layer from the optical coherence tomography were effective in localising drusen and hyperpigmentation beneath the photoreceptors. Cone photoreceptors in normal older eyes were shorter than in younger eyes. Cone photoreceptors survived in regions of atrophy, but with greatly reduced and highly variable density. Regular arrays of cones were found in some locations, despite abnormal retinal pigment epithelium. For some subjects, the cone density was significantly greater than normative values in some retinal locations outside the atrophy.

SUMMARY

The survival of cones within atrophy is remarkable. The unusually dense packing of cones at some retinal locations outside the atrophy indicates more fluidity in cone distribution than typically thought. Together these findings suggest strategies for therapy that includes preserving cones.

Distances From Capillaries to Arterioles or Venules Measured Using OCTA and AOSLO

Purpose

To investigate distances from retinal capillaries to arterioles or venules noninvasively.

Methods

An adaptive optics scanning laser ophthalmoscope (AOSLO) and optical coherence tomography angiography (OCTA) imager acquired detailed maps of retinal vasculature. Using OCTA, we quantified the distance from the edge of an arteriole or venule to the middle of the nearest capillaries (periarteriole or perivenule capillary-free zones, respectively) within the superficial vascular plexus of 20 young healthy subjects with normal axial lengths. These distances were compared to AOSLO images for three subjects. We tested the relation between the peripheral capillary-free zones and FAZ horizontal, vertical, effective diameters, and asymmetry indices in the deep vascular plexus. We examined enlargement with OCTA of capillary-free zones in a type 2 diabetic patient.

Results

The periarteriole capillary-free zone (67.2 ± 25.3 μm) was readily visible and larger than the perivenule capillary-free zone (42.7 ± 14.4 μm), F_{(1, 998)} = 771, P < 0.0001. The distance from foveal center (P = 0.003) and diameter (P = 0.048) were predictive of perivenule capillary-free zone values. OCTA and AOSLO corresponded for arterioles. FAZ effective diameter was positively associated with asymmetry indices, r = 0.49, P = 0.028, but not peripheral capillary-free zones, although focal enlargements were found in a diabetic patient.

Conclusions

For normal retinas, periarteriole and perivenule capillary-free zones are readily visible with OCTA and AOSLO. Periarteriole capillary-free zones were larger, consistent with arterioles carrying oxygen rich blood that diffuses to support the retina.

Adaptive optics imaging of the human retina

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.