Scanning laser ophthalmoscope design with adaptive optics

A design for a high-resolution scanning instrument is presented for in vivo imaging of the human eye at the cellular scale. This system combines adaptive optics technology with a scanning laser ophthalmoscope (SLO) to image structures with high lateral (∼2 μm) resolution. In this system, the ocular wavefront aberrations that reduce the resolution of conventional SLOs are detected by a Hartmann-Shack wavefront sensor, and compensated with two deformable mirrors in a closed-loop for dynamic correction and feedback control. A laser beam is scanned across the retina and the reflected light is captured by a photodiode, yielding a two-dimensional image of the retina at any depth. The quantity of back-scattered light from the retina is small (0.001% of reflection) and requires the elimination of all parasite reflections. As an in vivo measurement, faint cellular reflections must be detected with a low-energy source, a supraluminescent laser diode, and with brief exposures to avoid artifacts from eye movements. The current design attempts to optimize trade-offs between improved wavefront measurement and compensation of the optical aberrations by fractioning the light coming to the wavefront sensor, better sensitivity by increasing the input light energy or the exposure time and the response speed of the system. This instrument design is expected to provide sufficient resolution for visualizing photoreceptors and ganglion cells, and therefore, may be useful in diagnosing and monitoring the progression of retinal pathologies such as glaucoma or aged-related macular degeneration