Do monsters under the bed keep your child awake at night? Or could it be the bogeyman hiding in the closet?

But what if your child’s fear of the dark doesn’t stem from some imaginary creature or irrational fear?

It’s a rare problem, but experts say a retinal disorder called congenital stationary night blindness could explain why some children are terrified of the dark… they can’t see.

Most people’s eyes adjust after a minute or two in the dark. But this adjustment never happens for people with congenital night blindness, even if they can see perfectly fine in the light.

The inherited eye disease causes the eye’s light-processing photoreceptors linked to night vision to malfunction, preventing those who have it from seeing in the dark.

Scottish researchers who study night blindness say the condition can cause an intense fear of the dark in children.

And this retinal disorder isn’t the only condition that can lead to night blindness. The most common causes are untreated nearsightedness and the degenerative retinal disorder retinitis pigmentosa. Studies also show that a diet deficient in vitamin A can lead to night blindness.

University of Florida researchers are aiming to uncover the secrets behind a protein that could help those who suffer from night blindness. The protein arrestin regulates how sensitive cells are to light.

But currently few treatments exist for children with congenital stationary night blindness.

And until science sheds more light on this condition, a nightlight may be the best solution for parents.