Capsule endoscopy artifact: the afterimage - 22/08/11
Doi : 10.1016/j.gie.2007.05.024
Lawrence J. Brandt, MD, Editor, At the Focal Point Section
| Commentary An afterimage is an optical illusion that occurs after one gazes directly at an image for a prolonged period of time and then looks away. A common afterimage is the bright glow that persists after staring at a light bulb or the sun for just a few seconds. Afterimages are caused when the eye’s photoreceptors are overstimulated and become desensitized or fatigued. When the eyes are then diverted to a blank space, the fatigued photoreceptors send out only weak signals and the colors become muted. The surrounding receptors that were not excited by that color, however, are still “fresh,” and send out a strong signal, which is interpreted as the opposite or complementary (red-green, yellow-blue, and white-black) color. In addition to such negative afterimages, there are also positive afterimages that appear in the same color as the original image; they are often quite brief and usually immediately followed by a negative afterimage, reflecting the adaptation process described above. In a visual disturbance called palinopsia, often experienced by those who have migraines, patients have an increased propensity for seeing afterimages, but color opposition need not occur. Why the electric circuitry of a computer would experience the same desensitization fatigue of the human retina is beyond this editor’s comprehension, but for now, I would heed the authors’ caveat regarding image interpretation and, perhaps more importantly, remember that to prevent damage to the eyes, never look directly at any bright light source, especially the sun. Lawrence J. Brandt, MD Associate Editor for Focal Points |
© 2007
American Society for Gastrointestinal Endoscopy. Publié par Elsevier Masson SAS. Tous droits réservés.
Vol 66 - N° 4
P. 820-821 - octobre 2007 Retour au numéro
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