These words refer to seeing, whether in a literal or a metaphorical way. Vision , at its most limited, can refer to the proper functioning of the eyes: 20-20 vision ; cataracts that blurred her field of vision . This extends readily to sharpness of understanding: a man with keen vision . In this sense, it can indicate thoughtfulness, foresight or acuity.

Sight is a less formal term for the same concept, except that it cannot refer by itself to understanding: injury that resulted in a complete loss of sight . Both these words can apply also to something seen. Vision , here, would indicate something seen in a dream or hallucination, or something that may be illusory, imaginary, ideal or supernatural: a vision that came to him in his sleep; a medium who summoned up a vision of his dead wife; his vision of a world free from war. Sight , here, may be a neutral reference to a look at something real: catching sight of the Southern Cross; the first sight he saw on disembarking. More informally, it can indicate anything that looks odd or extraordinary: a badly overdressed woman who thought she looked a vision but was merely a sight .

Perception can refer, like vision , to seeing, but it is more general in referring to the action of any of the other senses, as well: lacking perception of greens and reds; a sharp perception of mildew and darkness in the unlit room. The word emphasizes not merely the registering of a phenomenon but the interpreting of it by the mind, often instantaneously: His trembling hands and blank stare confirmed her earlier perception that he was extremely ill at ease. Carrying this tendency further, the word can indicate, like vision , any sharpness of understanding: a critic of keen perception .

Eyesight would seem to add nothing to the idea of sight itself, since no other organs than the eyes are able to see. Yet the word is firmly established in usage: insured against the loss of eyesight . The word does select out the strict reference to seeing from sight’s other reference to whatever is viewed.