Dogs don’t do red eye

I’ve been pestered of late by Gavin at work to communicate to the world at large the fact that dogs don’t get red-eye. Quite an interesting fact, but not one that saw me running to the keyboard. Anyway, apparently dogs rarely get red-eye in photographs; instead, they get blue-, yellow- or green-eye. Here’s the science.

Apparently, if the eye was perfect, none of the eye-colouring effects mentioned above would happen. The retina of the eye would perfectly reflect the camera’s flash, it would end up reflecting back into the flash, and none of the associated light would enter the camera’s lens. The reality is somewhat different.

The red is apparently the reflection of the flash from the blood vessels at the back of the eye, and lighter-coloured eyes exhibit the behaviour more than darker eyes.

Most domestic animals have a reflective layer at the back of the eye (the tapetum) which enhances nocturnal vision. The colour of the tapetum is dependent on the colour of the animal’s coat, and it is the colour of the tapetum that determines the colour of the reflection, as opposed to the blood vessels that us humans have. Black labradors’ tapeta are usually green; cocker spaniels’ are yellow; most puppies have a blue tapetum before the eye becomes fully mature.

You heard it here first…


2 Responses to “Dogs don’t do red eye”

  1. Rob on August 20th, 2006 17:23

    Hate to burst your (Gavin’s?) bubble, but it would appear the world already knows:

    “In many species the tapetum lucidum, a light-reflecting layer behind the retina that improves night vision, intensifies this effect. This leads to variations in the colour of the reflected light from species to species. Cats, for example, display blue, yellow, pink, or green eyes in flash photographs.”

  2. Gav on August 20th, 2006 22:21

    I guess the question is did you know it before the blog post or did the blog post itself drive you to search the web? If it’s the former then my bubble is well and truly burst. However, in my defence, the guys in the office did not know this fascinating fact before I brought it to their attention.

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