Red Eyes - Dead or Alive?

Factual Questions
1

Hi

I recently saw on some crime show that the red eye phenomenon in photographs only occurs in living people. So if you take a photo of a dead body, they won’t have red eyes.

I was wondering if this is true?

Cheers,
Ting

2

Red eye is caused by light reflecting off the blood vessels in the retinas. The more open the pupils are, the more light will reflect and the more pronounced the red eye is.

IIRC the pupils in a dead eye are fairly wide open (at least at first; dunno if rigor mortis would cause them to contract) so more light would reflect off the retinas. Whether that reflected light would be red or some other color I don’t know.

3

Why do people have red eyes in flash photographs?

Since the red color is produced by blood, I would guess that once blood stops circulating and begins to coagulate the eyes would no longer reflect red.

4

Never thought about this before, but I’m quite intrigued. I’d love to hear Cecil’s answer to this question.

5

Well, as a photographer who has seen the effect often, I can say that it occurs when your subject is looking directly at the camera. Most dead people are horizontal and it’s terribly hard to get their attention. So it’s hard to imagine the camera angle that would be required to demonstrate the red eye effect. (Maybe autopsy photos?)

So, yes, I can see that it would be very unusual to get the red eye effect with a dead person, even without hypothesizing any physiological changes. But that’s not any more astonishing than the fact that they don’t say “cheese” and smile for the camera.

6

The key point is the red is a reflection of oxygenated blood moving through the dense capillary bed in the eye. When the heart stops, blood is no longer oxygenated. Arterial blood turns from a bright red, to burgandy to brown.
Also, the blood is no longer moving. I believe the reflectiopn is possible because the blood is moving. I guess it would be a bit like light on moving water.
If a photo was snapped within say, 1 minute after the vital functions cease, you might see red eye, longer than that, no.

The iris does remain dialated, but the cornea becomes cloudy after several hours.