Dr. Duncan and her colleagues have superimposed images produced by scanning laser ophthalmoscopes on images produced by spectral domain optical coherence tomography (SD-OCT) and fundus autofluorescence (FA) to create cross-sectional images in three dimensions. In this way, they can follow changes in individual cones over time, noting their spacing, packing, and density.
Such measures as the average distance between cones in a mosaic can provide a sensitive, reliable, repeatable outcome measures for disease progression in eyes with inherited retinal degeneration, said Dr. Duncan.
The confocal system provides images of photoreceptors with intact inner and outer segments that are in contact with retinal pigment epithelial (RPE) cells. But photoreceptors with outer segments that are disrupted, detached, or misaligned may not be visible in confocal images, she said.
For this reason, Dr. Duncan and other researchers are exploring the use of non-confocal techniques. One such technique using split detection to capture non-confocal images can resolve intervening rods, show cone inner segments even in the absence of outer segments, and can reveal RPE cells, allowing them to be reliably identified.
Since the technique does not rely on confocal images of direct, backscattered light, a split detector adaptive optics image might reveal structures even when cones are not wave-guiding and scattering normally. Images produced this way might reveal the photoreceptor inner segments in cases where the outer segments are disrupted, misaligned, or absent, which would not give rise to a confocal, wave-guided image.