Purkinje images are reflections of objects from structure of the eye. They are also known as Purkinje reflexes and as Purkinje-Sanson images. There are at least four Purkinje images that are visible on looking at an eye. The first Purkinje image (P1) is the reflection from the outer surface of the cornea. The second Purkinje image (P2) is the reflection from the inner surface of the cornea. The third Purkinje image (P3) is the reflection from the outer (anterior) surface of the lens. The fourth Purkinje image (P4) is the reflection from the inner (posterior) surface of the lens. Unlike the others, P4 is an inverted image. Purkinje-Sanson images are named after Czech anatomist Jan Evangelista Purkyně (1787-1869) and after French physician Louis Joseph Sanson (1790-1841). The third and fourth Purkinje images can be visible from within the eye itself. Light reflected away from the surfaces of the lens can in turn reflect back into the eye from the rear surface of the cornea. These images are, por lo tanto, entoptic phenomena. The first and fourth Purkinje images are used by some eye trackers, devices to measure the position of an eye. Brightness of Purkinje Images The brightness of the Purkinje images can be determined using Fresnel's equation where the Purkinje image I is the brightest of the four then PII, PIII and PIV (III and IV have about the same brightness). The Purkinje images can be used to assess the curvatures and separations of the surfaces in the eye. See also Red-eye effect External links Explanation of using purkinje images for eye tracking. ---> v·d·e Phenomena of the visual system Entoptic phenomena Blind spot Phosphene Floater Afterimage Haidinger's brush Prisoner's cinema Blue field entoptic phenomenon Purkinje images Other phenomena Aura Form constant Scintillating scotoma Palinopsia Visual snow Afterimage on empty shape Cosmic ray visual phenomena Scotopic sensitivity syndrome Template:Eye navs This page uses Creative Commons Licensed content from Wikipedia (ver autores).
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