page_title: Red-eye effect
section_title: Causes
hierarchical_section_title: Red-eye effect / Causes
caption_attribution_description: Brazilian odd-eyed white cat "Shiro"
context_page_description: The red-eye effect in photography is the common appearance of red pupils in color photographs of the eyes of humans and several other animals. It occurs when using a photographic flash that is very close to the camera lens in ambient low light.
context_section_description: In flash photography the light of the flash occurs too fast for the pupil to close, so much of the very bright light from the flash passes into the eye through the pupil, reflects off the fundus at the back of the eyeball and out through the pupil. The camera records this reflected light. The main cause of the red color is the ample amount of blood in the choroid which nourishes the back of the eye and is located behind the retina. The blood in the retinal circulation is far less than in the choroid, and plays virtually no role. The eye contains several photostable pigments that all absorb in the short wavelength region, and hence contribute somewhat to the red eye effect. The lens cuts off deep blue and violet light, below 430 nm (depending on age), and macular pigment absorbs between 400 and 500 nm, but this pigment is located exclusively in the tiny fovea. Melanin, located in the retinal pigment epithelium (RPE) and the choroid, shows a gradually increasing absorption towards the short wavelengths. But blood is the main determinant of the red color, because it is completely transparent at long wavelengths and abruptly starts absorbing at 600 nm. The amount of red light emerging from the pupil depends on the amount of melanin in the layers behind the retina. This amount varies strongly between individuals. Light-skinned people with blue eyes have relatively low melanin in the fundus and thus show a much stronger red-eye effect than dark-skinned people with brown eyes. The same holds for animals. The color of the iris itself is of virtually no importance for the red-eye effect. This is obvious because the red-eye effect is most apparent when photographing dark-adapted subjects, hence with fully dilated pupils. Photographs taken with infrared light through night vision devices always show very bright pupils because, in the dark, the pupils are fully dilated and the infrared light is not absorbed by any ocular pigment.
  The role of melanin in red-eye effect is demonstrated in animals with heterochromia: only the blue eye displays the effect. The effect is still more pronounced in humans and animals with albinism. All forms of albinism involve abnormal production and/or deposition of melanin.
  Red-eye effect is seen in photographs of children also because children's eyes have more rapid dark adaption: in low light a child's pupils enlarge sooner, and an enlarged pupil accentuates the red-eye effect.
  Theatrical followspot operators, positioned nearly coincidentally with a very bright light and somewhat distant from the actors, occasionally witness red-eye in actors on stage. The effect is not visible to the rest of the audience because it is reliant on the very small angle between the followspot operator and the light.
caption: This odd-eyed cat displays red-eye effect of its tapetum lucidum only in its blue eye
exif: {"Image ImageDescription": "", "Image Make": "NIKON", "Image Model": "E2100", "Image Orientation": "Horizontal (normal)", "Image XResolution": "300", "Image YResolution": "300", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop 7.0", "Image DateTime": "2007:07:22 01:48:45", "Image ExifOffset": "213", "EXIF ExposureTime": "10/601", "EXIF FNumber": "17/5", "EXIF ExposureProgram": "Program Normal", "EXIF ISOSpeedRatings": "100", "EXIF ExifVersion": "0220", "EXIF DateTimeOriginal": "0000:00:00 00:00:00", "EXIF DateTimeDigitized": "0000:00:00 00:00:00", "EXIF CompressedBitsPerPixel": "2", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "3", "EXIF MeteringMode": "Pattern", "EXIF LightSource": "Unknown", "EXIF Flash": "Flash fired, auto mode", "EXIF FocalLength": "81/10", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "236", "EXIF ExifImageLength": "232", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF DigitalZoomRatio": "0", "EXIF FocalLengthIn35mmFilm": "62", "EXIF SceneCaptureType": "Standard", "EXIF GainControl": "None", "EXIF Contrast": "Normal", "EXIF Saturation": "Normal", "EXIF Sharpness": "Normal", "EXIF SubjectDistanceRange": "0"}