Abstract
Purpose::
Our knowledge of retinal disease pathogenesis and progression has been confined to snap shots of histopathology, often after the animal has been sacrificed. In vivo retinal imaging is a powerful tool that allows the follow up of a disease process and effect of therapy, in the same animal over time. However, in vivo imaging of the retina in the mouse does not achieve the best possible resolution due to wavefront aberrations induced by the eye. Since adaptive optics has been successful in correcting phase aberrations in ophthalmic imaging of humans, we have used adaptive optics to correct aberrations introduced by the mouse eye.
Methods::
We have integrated an adaptive optics system into a fluorescence biomicroscope for imaging the mouse retina in vivo. The system provides imaging at video rate (30 fps) with an image field of approximately 0.5 mm square on the retina using excitation wavelengths of 635 nm (Evans Blue) and 491 nm (GFP). The adaptive optics system uses a Boston Micromachines MEMS deformable mirror with 140 actuators, each with a 3.5 micrometer stroke. The wavefront sensor is a Shack Hartmann wavefront sensor, which detects the fluorescent wavefront from the mouse retina.
Results::
Anesthetized C57BL/6 or B6.129P-Cx3cr1 tm1Litt /J mice were placed on a heated microscope stage and their eyes were covered with a lubricating agent (Methocel). A glass cover slip was positioned on the anterior surface of the cornea for visualization. Resident glial cells of the retina, microglia, express GFP in the transgenic B6.129P-Cx3cr1 tm1Litt /J mice. In C57BL/6 mice, Evans Blue (0.2-1%) was injected to label the vasculature. All mice received a drop of tropicamide 1% to dilate the pupil. Using the adaptive optics system we were able to visualize the retinal capillary bed labeled with Evans Blue, and dendrites of GFP+ microglia. A 50% increase in image brightness and a 7% increase in the Michelson contrast were measured.
Conclusions::
Using adaptive optics we have corrected wavefront aberrations in the mouse eye and increased imaging resolution. This technological advance will allow in vivo study of retinal disease pathogenesis and progression at the cellular level.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retina • microglia