出典:Wiktionary
出典:Wikipedia
出典:『Wikipedia』 (2011/05/28 15:56 UTC 版)
Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of visual photoreceptor, cone cells. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. On average, there are approximately 92 million rod cells in the human retina. More sensitive than cone cells, rod cells are almost entirely responsible for night vision.