In archaeology, the term entoptic phenomena relates to visual experiences derived from within the eye or brain (as opposed to externally, as in normal vision). In this respect they differ slightly from the medical definition, which defines entoptic phenomena as only applying to sources within the eye, not the brain. To avoid this confusion, the term subjective visual phenomena is sometimes used. Entoptic was chosen by author David Lewis Williams due to its origin from Greek meaning "coming from within".