- Purkinje images
Purkinje images are
reflection s of objects from structure of theeye . They are also know as Purkinje reflexes and as Purkinje-Sanson images. There are at least four Purkinje images that are visible on looking at an eye. Thefirst Purkinje image (P1) is the reflection from the outer surface of thecornea . Thesecond Purkinje image (P2) is the reflection from the inner surface of the cornea. Thethird Purkinje image (P3) is the reflection from the outer (anterior) surface of the lens. Thefourth 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 Frenchphysician 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, therefore, entoptic phenomena.
The first and fourth Purkinje images are used by some
eye tracker s, devices to measure the position of an eye.ee also
*
Red-eye effect 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.
External links
*Explanation of using purkinje images for eye tracking (http://www.diku.dk/~panic/eyegaze/node9.html).
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