Angioscotoma

An angioscotoma is a localized area of lower or absent visual sensitivity that follows the course of a retinal blood vessel. Because light‑sensitive photoreceptors lying beneath the retinal blood vessels receive less illumination, they send reduced or absent signals to the brain, creating blind regions that normally go unnoticed, since retinal adaptation suppresses awareness of this, similar to how the central blind spot is invisible. Angioscotomas are best revealed with specialized forms of perimetry and psychophysical testing. The magnitude of the defect depends on vessel calibre, eccentricity, and stimulus parameters. It has been shown in squirrel monkeys that angioscotoma casts a "shadow" on the retinotopic map of the visual field in the visual cortex.