Heterochromia iridis is when a person has two different coloured eyes, which is a rare condition, affecting around six in 1,000 people.

Sometimes this is very noticeable, for example if someone has one brown and one blue eye, but sometimes it's much subtler, e.g. one brown and one hazel eye.

In most cases, it's nothing to worry about - but it can be linked to a medical condition such as Waardenburg Syndrome, Horner's Syndrome or Sturge-Weber Syndrome.

Eyes can also change colour later in life. This could be caused by:

1. Glaucoma (a condition where the eye's optic nerve is damaged)

2. Taking medication to lower eye pressure

3. A benign tumour/abcess of the iris

4. Eye cancer

5. Trauma to the eye (e.g. in an accident)

If a child is born with heterochromia, it's unlikely that they have any other eye or health problems - Sometimes blood tests and chromosome studies are done, if it looks like they may have other medical conditions.

Benedict Cumberbatch’s specific condition is known as secoral heterochromia and explains why his eyes seem to change from green to blue, depending on the light.

More Info: www.thesun.co.uk