Identification of a subtype of cone photoreceptor, likely to be blue sensitive, in the human retina

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Abstract
A minor population of cone photoreceptors (called B‐cones) can be distinguished from the major population (called R‐cones) on morphological criteria as seen by light microscopy in foveal and peripheral human retina. The B‐cones are characterized by (1) a longer inner segment projecting into subretinal space, (2) a larger‐diameter inner segment, (3) an increased staining intensity of the inner segment, and (4) a different distribution relative to the R‐cones in the cone mosaic. B‐cones occur even in the foveolar center (3–5%) and rise to a maximum (15%) in the foveolar slope. They can also be identified in peripheral retina where they form 7–10% of the total cone population. The B‐cone population follows the distribution profile postulated for the blue‐sensitive system from histochemical studies on monkeys and from psychophysical studies on humans. The B‐cones also share many of the same morphological features of the putative blue cones of the ground squirrel and monkey retinas. For these reasons we suggest that our B‐cone group is the blue cone population of the human retina.