The Purkinje effect and Purkinje images
Stories from Physics
for 11-14
14-16
Jan Evangelista Purkyně, a 19th century Czech anatomist, gave his name to several well-known effects.
Depending on the intensity of lighting, we see colours differently. The wavelengths of light the human eye is sensitive to vary with the intensity of light, an effect known as the Purkinje effect. In lower intensity lights, peripheral rod cells are stimulated and the eye’s peak sensitivity to light shifts towards green in comparison to a peak sensitivity to yellow for vision in daylight. For example, in twilight, a red flower may appear black and objects in moonlight may appear greyish-green.
A separate phenomenon is the series of reflections that occur from the structures of the eye, known as Purkinje images. The first Purkinje image occurs due to reflection from the anterior surface of the cornea, the second from the posterior surface of the cornea, the third from the anterior surface of the lens, and the fourth from the posterior surface of the lens and is inverted. The reflections can be used by eye tracking technology to determine the movement of the eye.
Purkyně enjoyed great fame due to his research. It is claimed correspondents needed only to address a letter to ‘Purkyně, Europe’ for the message to reach him.
References
J. B. Sidgwick, R. C. Gamble, Amateur Astronomer’s Handbook, New York, NY, Dover Publications, Inc., 1971, p. 429.
G. Dai, Wavefront Optics for Vision Correction, Washington, Society for Photo-Optical Engineers, 2008, p. 168.
J. Bažant, N. Bažaåntová, & Frances Starn, The Czech Reader: History, Culture, Politics, Durham, Duke University Press, 2010, p. 150.
Zia Chaudhuri, Postgraduate Ophthalmology, Volume Two, New Delhi, Jaypee Brothers Medical Publishers, p. 1746.
