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Purkinje images are reflection
Reflection

Reflection or reflexion may refer to:...
s of objects from structure of the eye
Eye

Eyes are Organ that detect light, and send signals along the optic nerve to the visual system and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system....
. 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
Cornea

The cornea is the transparency front part of the eye that covers the Iris , pupil, and anterior chamber. Together with the cilliary muscles, the cornea reflects light, and as a result helps the eye to dilate, accounting for approximately two-thirds of the eye's total optical power....
. 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
Lens (anatomy)

The lens is a transparent, Lens_#Types_of_lenses structure in the eye that, along with the cornea, helps to refract light to be Focus on the retina....
.






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Purkinje images are reflection
Reflection

Reflection or reflexion may refer to:...
s of objects from structure of the eye
Eye

Eyes are Organ that detect light, and send signals along the optic nerve to the visual system and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system....
. 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
Cornea

The cornea is the transparency front part of the eye that covers the Iris , pupil, and anterior chamber. Together with the cilliary muscles, the cornea reflects light, and as a result helps the eye to dilate, accounting for approximately two-thirds of the eye's total optical power....
. 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
Lens (anatomy)

The lens is a transparent, Lens_#Types_of_lenses structure in the eye that, along with the cornea, helps to refract light to be Focus on the retina....
. 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
Czech people

Czechs are a West Slavs people of Central Europe, living predominantly in the Czech Republic. Small populations of Czechs also live in Slovakia, Austria, United States, Brazil, Argentina, Canada, Germany, Russia and other countries....
 anatomist Jan Evangelista Purkyne
Jan Evangelista Purkyne

Jan Evangelista Purkyne was a Czech Republic anatomist, patriot, and physiology....
 (1787-1869) and after French
French people

French people can refer to:* The legal residents and citizens of France, regardless of ancestry. For a legal discussion, see French nationality law....
 physician
Physician

A physician, medical practitioner, doctor of medicine, or medical doctor practices medicine, and is concerned with maintaining or restoring human health through the study, diagnosis, and treatment of disease and injury....
 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
Entoptic phenomenon

This is a medical definition of entoptic phenomena. For an alternative use within archaeology please see Entoptic phenomena Entoptic phenomena are visual effects whose source is within the eye itself....
.

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
    Red-eye effect

    The red-eye effect in photography is the common appearance of red pupils in color photographs of eyes. It occurs when using a photographic Flash very close to the camera lens , in ambient low light....


External links

  • Explanation of using purkinje images for eye tracking (http://www.diku.dk/~panic/eyegaze/node9.html).