1. The normal refractive condition of the eye in which there is clear focus of light on the retina. 2. An ideal optical condition when parallel light rays come to a focus on the retina.
3. That refractive condition of the eye in which the rays of light are all brought accurately and without undue effort to a focus upon the retina; opposed to hypermetropia (farsightedness), myopia (nearsightedness), and astigmatism; or the refractive condition of the eye in which the rays of light are all brought accurately, and without undue effort, to a focus upon the retina.