Another non-confocal technique, dark-field adaptive optics scanning laser ophthalmoscopy (AOSLO), can attenuate backscatter light from photoreceptors to show RPE cells.
A third non-confocal technique, multiple offset detection, can reveal cone inner segments at the margins of geographic atrophy in age-related macular degeneration.
Applied to microperimetry, AOSLO can deliver small visual stimuli precisely to individual cones or small groups of cones. Combined with high-speed fundus tracking, this technique can be used to test cone function in areas where cones are not visible in confocal images.
An example of the way the AOSLO can be used, acute foveolitis reduced the visual acuity of a 21-year-old woman to 20/80. No cones were visible in her fovea. Five years later, her visual acuity had recovered to 20/25, with improved visual function in regions where cones were still not visible, but the external limiting membrane was slightly hyper-reflective in cross-sectional OCT scans through the fovea.
AOSLO was used to deliver spots of light precisely to regions where cones were not visible using confocal images, and measures of visual function provided evidence of residual cones that could not be seen with other imaging modalities.