Red eye occurs because when you take a flash photograph - the camera produces a big burst of light to illuminate the subject and that burst of light goes in through the open pupil of the subject, and bounces off the back of the eye.   There’s a layer called the choroid which has a very rich blood supply inside the eyeball and that reflects red light, the colour of the blood, back out of the front of the eye and into the camera.  This happens so quickly that there’s not time for the pupil to contract before the camera takes the picture.  So you see this red reflection of the interior of the person’s eyeball.  

Red eye reduction works by the camera shining a brightish light or doing a few ‘spoof’ flashes at the subjects first.  This constricts the pupil down in the people you're taking a picture of, and then it takes the proper picture.  This means that there’s a very small aperture in the front of the eye as the pupil has got very tiny, therefore much less light gets in and it’s much harder for light to reflect back out again.  And that’s how red eye reduction occurs.

Why are some people more prone than others?  Perhaps, the pictures that you've been taken in are not pictures involving flash photography, so you don't seem to have the effect.  Perhaps also, you're not directly in line with the camera flash.  If the flash didn’t actually illuminate the eyeball sufficiently on its interior, not enough light will come back out of the camera.  One other possibility is that you have very, very dense pigment epithelium.  This is a layer of melanin (the same stuff that gives you a sun tan) inside the eye and that’s what soaks up some of the extra light.  

People also naturally differ in how wide their pupil is in any particular light.  People with wider pupils are more likely to end up with red eye in photos, whereas those with smaller pupils are less likely.

We put this to Graeme Alexander:

Graeme -   The liver cells are part of a complicated organ - the liver - where there’s lots of different types of cells.  There’s another cell sitting next to the liver cell called a stellate cell and there are signals sent out by an injured liver cell to those stellate cells which scar the liver.  So the liver ends up being scarred in exactly the same way as someone who’s had an operation and there’s a scar on their skin, but this scar is spread finely and diffusely throughout the whole liver.

We put this to Graeme Alexander:

Graeme -   When I meet patients in the clinic, I get two types of question.  One, from a patient who’s scared that they’ll transmit hepatitis B to someone they love  - and then the other, from the person that they love, wondering if they’ll catch it from their partner.  And the answer is that you can't catch hepatitis B from urine.  These viruses are actually quite difficult to catch, both hepatitis B and hepatitis C.  And hepatitis B is acquired largely by contact with blood or through sex and hepatitis C pretty well only by contact through blood.  So, you can live with someone for many, many years and not catch hepatitis B or C from them because close contact in the family situation is entirely safe.

Chris -   And I think the other mitigation is that there is a good vaccine for hep-B, isn’t there?  So if we identify people in a family situation who have one carrier and one person who isn’t infected, we can vaccinate the uninfected person to protect them.

Graeme -   It’s probably the most effective vaccine that we’ve ever come across, very effective and very safe once you've been vaccinated.

Yes, certainly money can be a vector for infection and as an example, lets look at norovirus, which causes winter vomiting disease (but more recently, vomiting all around the world at all times of the year – it’s becoming incredibly common).  Norovirus is a tiny particle, one 30,000th of a millimetre across, can very easily be transmitted from one surface to another.  They can survive seven changes - so if you touch something, and someone else touches it and picks it up, they can then transfer it seven times and the virus still remains infectious.  You only need to pick up one of them to get infected.  Yuck!

We put this to Graeme Alexander:

Graeme -   Well a lot of viruses can affect the liver, but there’s five that we recognize as important in the liver and they're HepatitisA, B, C, D, and E - rather imaginative aren’t we?

The most important thing about hepatitis C is that it, by and large causes an infection that lasts for a lifetime while the other viruses don't (usually).  So that differentiates it quite easily.  And it’s an RNA virus whereas hepatitis B is a DNA virus infection.  But that’s sort of a semantic difference.  The important thing about hepatitis C is that it causes lifelong infection in many people.