Night blindness casts bogeyman into the shadows

Dermot McGrath
in Glasgow, Scotland

THE bogeyman has traditionally taken the blame for children’s fear of the dark. But researchers in Scotland believe that a type of nyctalopia — or night blindness — could be the real culprit in some cases.

In an article published in the British Medical Journal, consultant ophthalmologist Gordon Dutton MD and his colleagues at Gartnavel General Hospital in Glasgow describe two children with an inherited form of stationary night blindness.
Both were very frightened of the dark, had a history of bumping into things at night and one child expressed a fear of shadows.

The first case was a three-year-old girl with no apparent visual problems who had always been scared of the dark. She complained to her parents of being able to see when the bedroom lights were off and refused to go to the bathroom, which was down a dark hallway, during the night. It was only when the girl’s younger sister was diagnosed with retinal problems that the parents had the older child’s eyes tested.

The second girl, aged two, also had a history of frequently tripping over and bumping into objects as well as problems seeing in the dark. Her parents reported that when she woke at night she would cry but would not go to her parents’ bedroom. She also needed to have curtains drawn at night because of her fear of the darkness beyond the windows.

In both cases, electrophysiology tests revealed a “negative” electroretinogram consistent with a diagnosis of congenital stationary night blindness.
Congenital stationary night blindness — so called because it doesn’t change throughout life — is rare and its prevalence has not been well established, although it is about three times more common in boys than in girls, according to the researchers.

The condition is an inherited, non-progressive disorder principally affecting rod photoreceptor function in the retina, resulting in impaired night vision, although there is commonly a mild impairment in cone function, which may affect daytime central visual acuity.
The defective pathway appears to result from a signal transmission defect from the photoreceptors.

It principally manifests itself as an increase of the dark adaptation threshold, nystagmus, and often moderate to high short-sightedness, although the refractive state may be far-sighted or normal. Squint, pale or tilted optic discs, and paradoxical pupil responses have all been linked to the condition.

There is usually no visual deficit in good lighting conditions but mild central visual loss is common in some inherited forms. Fundus examination is usually normal, distinguishing it from the progressive conditions causing nyctalopia.

The researchers said children’s fear of the dark is often dismissed as little more than attention-seeking behaviour or irrational fear that will fade over time.
They recommend that in cases where children are afraid of the dark, doctors need to take a full family history to find out about visual problems. This should then be followed by a complete ocular examination and electroretinography to determine whether the children are suffering from night blindness.

“Night blindness in children can bring about profound fear of the dark. Recognition of the diagnosis and the simple expedient of giving the child control of lighting conditions can transform family life,” the researchers’ report concluded.

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