A uncommon trait noticed on Madeleine McCann on posters and TV after her disappearance only effects one in every 10,000 births.
Her misshaped pupil is due to a condition called coloboma. But what does it mean and what are the effects?
What is coloboma?
Coloboma is a gap in part of the eye’s structure, normally towards the bottom of the eye.
It can affect just one or both eyes, and does not mean that there is a hole in the eyes – just that they did not fully form during pregnancy.
Coloboma can affect the iris, lens and retina.
It is hard to tell how much a child’s vision has been affected until they are older.
The most common form of coloboma is the one affecting the iris – often giving the sufferer a pupil shaped like a keyhole.
Children with this form tend to have fairly good vision, although they might dislike bright lights.
How common is coloboma?
Coloboma is extremely rare, only occurring in one in 10,000 births, while Maddie’s mark could affect as few as seven out of one million people.
Speaking of facial recognition software, retired detective chief inspector Mick Neville told The Sun: “If an image search was carried out for females in an age range of three to 15 with this eye marking then you may only have a few hundred in the UK and tens of thousands worldwide.
“It would be an easily manageable number to scan through.”
What causes coloboma?
Coloboma occurs when a baby’s eye or eyes do not develop properly during pregnancy – which happens between the fourth and 15th week after conception.
Sometimes it is inherited, but in most cases there is not a genetic link.
However, if your child has coloboma then you yourself should get your eyes tested – in case you have undiagnosed problems.
Not much is known about other causes of coloboma.
How is coloboma treated?
Coloboma cannot be cured – but is monitored with six monthly and then yearly eye checks.
Some children with coloboma may need to wear glasses, and adults can get cosmetic contact lenses to make the pupil look round.
Prescription sunglasses are sometimes advised, because of the light sensitivity.
Where did Madeleine McCann go missing?
Little Maddie, then three, disappeared from her bed in a holiday apartment in Rua Dr Agostinho da Silva, Praia da Luz, a resort in the Algarve region of Portugal.
The McCanns arrived on Saturday, April 28, 2007, for a seven-night spring break at the two-bedroom, ground-floor apartment.
It was in the fifth block of a group of apartments known as Waterside Village.
But on the evening of May 3, the little girl vanished from the apartment where she had been sleeping with her brother and sister.
Her parents were at a nearby restaurant.