The use of AO imaging systems to image the living human retina is becoming increasingly widespread. A number of groups are utilizing AO technology to examine photoreceptors in the normal (Roorda and Williams 2002
; Putnam et al. 2005
; Jonnal et al. 2010
) and diseased (Choi et al. 2006
; Wolfing et al. 2006
; Duncan et al. 2007
; Carroll et al. 2008
; Chen et al. 2010
) retina. Owing to their high contrast, identifying cones in AO images has proved relatively easy – semi-automated techniques to identify cone photoreceptors are now widely used (Li and Roorda 2007
; Rossi and Roorda 2010
). Thus a major focus in the analysis and interpretation of AO images has been density, spacing, or regularity of the cone mosaic. However, we believe that there may exist other important features in these images that may not get captured by these metrics. It is important to establish what other features should be captured from these images and begin to discuss what they might mean, specifically with regard to photoreceptor health.
Here, we describe three cases with unusual AO retinal images. This descriptive case series demonstrates that while AO imaging has shed enormous light on the cellular basis of visual abnormalities in retinal degenerations, several questions remain. While the underlying disease etiology is uncertain in these examples, the presence or absence of the cones is secondary to potentially more meaningful features involving the photoreceptor mosaic. A similar logic applies to optical coherence tomography images - there is more data to be gained from these images than just retinal or sub-layer thickness (i.e., inner segment/outer segment (IS/OS) reflectivity). Continued development of new image analysis metrics should increase the clinical utility of both imaging modalities.