Ultrastructural description of a "cylinder organelle" in the outer plexiform layer of human retinas.

A cylinder-like organelle ("cylinder organelle") present in the outer plexiform layer of the retina and apparently confined to the horizontal cell processess is described. This structure was studied in detail in three normal human retinas from eyes enucleated for ciliary body melanomas. The cylinder organelle, when cut longitudinally, showed an electron-lucent area bound by two bands of electron-dense filaments. In transverse section, the cylinder organelle revealed a circular profile of electron-dense crisscrossing filaments about an electron-lucent matrix. Since this structure was only found in the rod spherule synaptic complex, it is hypothesized that it may be involved in transmitting impulses.