It is rare, but some people have eyes that are different colours, usually one blue eye and one green or brown one. This condition is called heterochromia and there are various reasons why this can happen, which we will examine below.
The colour change within the eye can be complete heterochromia which means the iris (the coloured part of the eye) is completely a different colour to the other, or segmental heterochromia which means that the iris is partially the ‘normal’ colour and partially the different colour. Let us look at the causes of heterochromia.
Genetic heterochromia happens in approximately six out of every 1000 people. For genetic heterochromia, both parents must carry the gene mutation that either causes the condition directly, or causes the illness that causes the eye colour to change. These conditions can present in the womb too, so a baby born with heterochromia could have it as a genetic mutation or as a result of the mother having a condition. However it happens, heterochromia that occurs before, during or very shortly after birth is considered to be ‘genetic’ heterochromia.
It is important to have any incidences of heterochromia checked out as sometimes the condition can be a symptom of a number of illnesses that can have other, more serious consequences. For example, Waardenburg Syndrome, which causes heterochromia, also causes deafness and colour changes in the skin and hair too. Tuberos sclerosis (also called Bourneville disease) causes benign tumours in organs such as the eyes. There are many similar conditions which can be managed, but they must be diagnosed early in order to minimise the long-term effects of these genetic issues.
Perhaps the most famous person with injury induced heterochromia was David Bowie, who had one pupil permanently dilated as well as the iris being a slightly different colour following a fist fight with a school friend over a girl. The two made up their differences, but Bowie’s eye was permanently damaged. The muscles responsible for contracting the pupil were paralysed by this injury, leaving the pupil permanently wide open.
When to see a doctor
As with genetic heterochromia, if you suffer any injury that causes a change to your eye, whether it is the pupil or the iris, be sure to seek medical help sooner, rather than later. Injuries can worsen if untreated, or cause eye infections and – in worse case scenarios – cause blindness and pain. It is always better to be safe than sorry.