Retinal vascular diseases are a leading cause of blindness and visual disability. The advent of adaptive optics retinal imaging has enabled us to image the retinal vascular at cellular resolutions, but imaging of the vasculature can be difficult due to the complex nature of the images, including features of many other retinal structures, such as the nerve fiber layer, glial and other cells. In this paper we show that varying the size and centration of the confocal aperture of an adaptive optics scanning laser ophthalmoscope (AOSLO) can increase sensitivity to multiply scattered light, especially light forward scattered from the vasculature and erythrocytes. The resulting technique was tested by imaging regions with different retinal tissue reflectivities as well as within the optic nerve head.

Abstract:We used a confocal adaptive optics scanning laser ophthalmoscope (AOSLO) to image the retina of subjects with nonproliferative diabetic retinopathy (NPDR). To improve visualization of different retinal features, the size and alignment of the confocal aperture were varied. The inner retinal layers contained clearly visualized retinal vessels. In diabetic subjects there was extensive capillary remodeling despite the subjects having only mild or moderate NPDR. Details of the retinal microvasculature were readily imaged with a larger confocal aperture. Hard exudates were observed with the AOSLO in all imaging modes. Photoreceptor layer images showed regions of bright cones and dark areas, corresponding in location to overlying vascular abnormalities and retinal edema. Clinically undetected intraretinal vessel remodeling and varying blood flow patterns were found. Perifoveal capillary diameters were larger in the diabetic subjects (p<0.01), and small arteriolar walls were thickened, based on wall to lumen measurements (p<.05). The results suggest that existing clinical classifications based on lower magnification clinical assessment may not adequately measure key vascular differences among individuals with NPDR.

Despite large individual variations in size and shape of the FAZ, the INLFAZ has a relatively constant thickness at the margins of the FAZ, suggesting the presence of retinal capillaries is needed to sustain an INLFAZ thickness greater than 60 μm. A smaller FAZ area is associated with a vertically elongated FAZ.

Imaging polarimetry was used to examine different components of neovascular membranes in age-related macular degeneration. Retinal images were acquired with a scanning laser polarimeter. An innovative pseudocolor scale, based on cardinal directions of color, displayed two types of image information: relative phases and magnitudes of birefringence. Membranes had relative phase changes that did not correspond to anatomical structures in reflectance images. Further, membrane borders in depolarized light images had significantly higher contrasts than those in reflectance images. The retinal birefringence in neovascular membranes indicates optical activity consistent with molecular changes rather than merely geometrical changes.

A new Mueller matrix polarimeter was used to image the retinas of normal subjects. Light from a linearly polarized 780 nm laser was passed through a system of variable retarders and scanned across the retina. Light returned from the eye passed through a second system of retarders and a polarizing beamsplitter to two confocal detection channels. Optimization of the polarimetric data reduction matrix was via a condition number metric. The accuracy and repeatability of polarization parameter measurements were within ± 5%. The magnitudes and orientations of retardance and diattenuation, plus depolarization, were measured over 15° of retina for 15 normal eyes.