|For vision scientists, the human retina promises to be a window into the health of a patient. A clear view of the retina in-vivo with high resolution detail of photoreceptors and vascular flow could give the vital detail that would enable clinicians to make early and accurate diagnosis of diseases. This window is blurred, however, by imperfections in the eye itself: the cornea and crystalline lens, as well as the viscous and non-uniform nature of the vitreous humor, prevents clinicians from viewing the important cellular structures. Optically, this image distortion of the retina stems from tissue-induced wavefront aberrations and results in a low resolution image. By actively correcting for wavefront aberration in the optical path between the imaging camera and the retina, adaptive optics has emerged as an enabling technology for retinal imaging with cellular-level resolution. This technology holds promise for non-invasive detection and diagnoses of leading eye pathologies such as glaucoma, diabetic retinopathy, and age related macular degeneration.
The two primary eye-imaging techniques that employ adaptive optics are confocal scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT). Confocal SLO attempts to scan laser light over the retina to create an image. Without adaptive optics, the best achievable resolution levels are in the 5-10 µm range—too low to resolve individual photoreceptor cells which are around 3 µm. However, retinal imaging using adaptive optics technology today can achieve 1 µm resolution levels, producing detailed images of photoreceptor cells, as seen in Figure 1. This image was created using a 140 actuator Multi-DM.
Images taken using a confocal SLO. Adaptive optics-on image
(right) shows increased signal, contrast, and 2-3 µm resolution enabling detail of individual
photoreceptor cells within the retina.
Credit Austin Roorda, U.C. Berkeley
Figure 2: OCT is an interferometric imaging technique that creates 3D scanned images. This figure shows cross-sectional images obtained with (right) and without (left) an adaptive optics spectral domain OCT (AO-SDOCT) system by D. X. Hammer, et. al, of Physical Sciences, Inc. In the OCT images taken with adaptive optics, the external limiting membrane (shown by the arrow) is better resolved, as are capillaries and structures in other retinal layers.