Cell count and density
Using AO, it is possible to count photoreceptor cells and calculate their density.
“Findings from calculations of AO-measured cone density versus eccentricity correlate nicely with the expected numbers from histology,” Dr. Chung said. “There is already normative data for cone density based on AO imaging,”
AO imaging in eyes with different pathologies highlights its capability for providing novel information. In a published report, Dr. Chung and colleagues used AOSLO to image the eyes of two brothers with early Stargardt disease and their unaffected parents. They compared the findings with those seen on imaging with other techniques [Song H, et al. JAMA Ophthalmol. 2015;133(10):1198-1203.]
AO revealed normal photoreceptor structure and spacing in the parents, but in the two brothers, it showed increased cone and rod spacing and a dark cone appearance in the periphery, which Dr. Chung said is thought to represent loss of the outer segments.
With AO, no foveal cones were detected in the eye of the older brother. In his sibling, the foveal cones were enlarged and reduced in density to ~25% of the normally expected value.
“OCT in the affected brothers showed loss of photoreceptor outer segments in a bull’s-eye pattern with foveal sparing, and a normal appearing peripheral photoreceptor layer,” Dr. Chung said.