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Retinal disease has been given a new face thanks to increased details of the adaptive optics scanning laser ophthalmoscope (AO-SLO), according to Mina Chung, MD.
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“AO-SLO imaging measures the wavefront aberrations and corrects them using a deformable mirror,” said Dr. Chung, associate professor of ophthalmology, Flaum Eye Institute, University of Rochester, NY. “The most recent designs allow for a 2-μm resolution that enables imaging of the cones at the foveal center, (and) rods can be resolved in the peripheral retina.”
With fluorescence AO-SLO, retinal pigment epithelium (RPE) fluorescence is used simultaneously to obtain images of the photoreceptors and the underlying RPE in the same retinal location.
Patients with retinal diseases can have poor fixation and ocular movements, which is challenging when attempting to obtain retinal images.
Investigators at the University of Rochester and Canon Inc. have developed a real-time, multi-scale stabilization system that uses a wide-field SLO with a tip/tilt mirror that compensates for gross movements, another closed-loop tip/tilt mirror in the AO-SLO to compensate for fine movements, and digital registration algorithms to remove the stabilized images, Dr. Chung said.
She described a patient with age-related macular degeneration (AMD) where the motion was corrected from 68 arc minutes to 0.08-arc minute, which allowed creation of an averaged image of the retina.
“These advances allow imaging in patients with poor fixation and poor vision,” she said.
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When investigators superimpose AO-SLO images on a fundus photograph, they are able to zoom in on the image.
“The cones appeared dark, which may suggest shortening of the outer segment and the rods were enlarged and visualized more easily,” Dr. Chung commented.
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Additional zooming in on the image allows counting of the rods and cones.
In another patient with AMD, a small area of extrafoveal geography atrophy (GA) was visualized supratemporally that was better visualized on autofluorescence imaging. When AO-SLO imaging was performed, every cone could be labeled, and cone-like cells appeared to be present in the GA lesion.
When all cones were labeled, she explained, the cone space can be calculated.
“The cone spacing outside of the GA lesion appeared to be consistent with the cone spacing of the cells within the GA lesion,” she said, but pointed out that further study is needed to confirm if the cells are actually cones.
“AO-SLO can show reflectance of cones and rods in single-cell resolution,” Dr. Chung said. “With autofluorescence, we can identify RPE cells. With image stabilization, we are better able to perform imaging in patients with poor fixation.
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“In patients with Stargardt’s disease, the technology demonstrates decreased cone and rod density, and in AMD there appear to be cone-like structures within small GA lesions,” she concluded.