Night blindness runs in our family: inherited retinal disease and when to test a child

Atuk never could see in the dark, and your husband needs a torch at dusk to find the car. Now your daughter hesitates at the top of the stairs when the lights are low, and you wonder whether this runs in the family and whether she should be tested.

This page is about inherited retinal conditions, the group of eye diseases that can pass down in families. It sets out the early signs in a child, what an eye exam, an electrical test of the retina and a gene test can and cannot tell us, and what help exists. Most children who see poorly in dim light do not have one of these conditions, and nothing here is a verdict on any child. An earlier look is simply kinder than a late one.

What is inherited retinal disease, and why does night blindness run in some families?

It is a group of conditions in which the light-sensing layer at the back of the eye, the retina, works less well because of a change in a gene. Retinitis pigmentosa is the best known. The American Academy of Ophthalmology's EyeWiki puts it at about 1 in 3,000 to 1 in 5,000 people.

The cells that work in dim light, the rods, are usually affected first, which is why poor vision in dim light is the most common early symptom according to AAPOS. The condition can pass down in a dominant, recessive or X-linked pattern, or appear with no family history at all.

That is why one family has a grandfather and a grandson with the same trouble, and another family has a single child with no one else affected. The action: write down which relatives have had night blindness, tunnel vision or early sight loss, and bring that list to the eye visit.

What are the early signs in a child?

In an older child, the first sign is usually trouble in dim light: slow to adjust when coming indoors, reluctant to walk in the dark, bumping into furniture at dusk, or needing more light to read. Side vision tends to go before central vision, so a child may knock into things she did not notice at the edge of her view. AAPOS notes that most people begin to have problems in their teenage years.

In a baby or toddler the picture can be different. EyeWiki describes one severe early form, Leber congenital amaurosis, with eyes that move or shake from birth or soon after, poor vision from the start, slow or weak pupil responses, sensitivity to bright light, and a habit of pressing or rubbing the eyes. It is rare, at two to three per 100,000 births. Wobbly eyes in a baby explains why shaking eyes need an examination. Another sign at any age is vision that glasses do not improve.

The action: if your child shows any of these, book an eye examination and do not wait for the next school screening.

Is trouble seeing in the dark always an inherited condition?

No, and most of the time it is not. Other eye problems can make dim light hard too, which is why the whole eye is examined. Low vitamin A causes night blindness too, a cause covered in vitamin A deficiency and children's eyes.

The AAO does not currently recommend vitamin A supplements for retinitis pigmentosa, so a bottle from the pharmacy is not a treatment for the inherited type. For the wider question of food and sight, see do carrots or fish oil improve eyesight. The action: have the eyes examined before changing the diet or buying a supplement, so that the cause is found rather than guessed.

Why does a family history mean an earlier eye check?

Because these conditions can begin before a child can describe them. A young child does not say "I cannot see in the dark"; she may hold your hand on the stairs and assume everyone does. A baseline examination in a child with a family history gives the doctor a starting point to compare against later.

A family history is a reason to check early and not a diagnosis. Many conditions that run in families do not reach every child. A different family condition, glaucoma, follows the same logic: see glaucoma runs in families: who should be checked, and from what age.

For a wider habit of checking, eye checks for the whole family covers it. The action: if a parent, grandparent or sibling has an inherited retinal condition, tell the eye doctor at your child's first visit, and bring any report or diagnosis name you have.

What can an eye exam and an ERG tell us, and what can they not?

The exam looks at the back of the eye, measures sight and the side vision as far as the child can cooperate, and may include a scan of the retinal layers. An electroretinogram (ERG) goes further. According to EyeWiki it measures the electrical response of the rods and cones to light, and is essential to the diagnosis of retinitis pigmentosa.

Two limits matter. First, the back of the eye can look normal early on, particularly in babies with the severe early forms, so a normal-looking exam does not exclude a problem, and the ERG can settle the question. In Leber congenital amaurosis a normal ERG effectively rules it out. Second, the tests describe how the retina is working now. They do not forecast how it will change, which varies even within one family. The action: if the doctor suggests an ERG, ask what the result would change in the plan.

What can genetic testing tell us, and what can it not?

A gene test can name the change behind the condition, help the doctor work out the inheritance pattern for the family, and show whether a specific treatment exists. It cannot always find an answer. EyeWiki says more than 100 gene locations are known, and about half of cases still have no gene identified. A result may also be "uncertain".

The American Academy of Ophthalmology's task force advises that skilled counselling go with every test, because a result can affect family plans and relationships, and can bring worry or guilt. It also advises avoiding tests on children with no symptoms for conditions that have no treatment, except in extraordinary circumstances and after formal counselling.

For a child who does have symptoms, the case for testing is stronger. The action: ask for genetic counselling, a written copy of the result, and a plain explanation of what each possible result would mean for other children and relatives.

Is there a treatment, and what helps at school and at home?

For most types there is no cure yet. For one narrow type there is a gene therapy. Voretigene neparvovec is approved for people with confirmed biallelic RPE65 mutation-associated retinal dystrophy, and in Europe for adults and children with enough viable retinal cells remaining.

It is given as an injection under the retina in each eye. It applies to this one type only, which is why a gene test matters. EyeWiki and the AAO also list low vision services, sunglasses that block ultraviolet and blue light, and treatment for complications such as cataract.

Daily support makes a real difference to a child. Low vision rehabilitation teaches ways of working and devices such as magnifiers. Teachers can be told so that seating, lighting and the walk home at dusk are managed. Some children also need glasses, and the eye doctor will check.

The action: if your child has been given a diagnosis, ask for a low vision referral and a letter for the school. If you are worried and have no diagnosis yet, an examination is the next step, and how we test children's eyes shows what it involves.

Common questions

References

1. American Academy of Ophthalmology EyeWiki · Retinitis Pigmentosa · eyewiki.aao.org
2. AAPOS · Retinitis pigmentosa · aapos.org
3. American Academy of Ophthalmology · What is retinitis pigmentosa? · www.aao.org
4. American Academy of Ophthalmology EyeWiki · Leber Congenital Amaurosis · eyewiki.aao.org
5. American Academy of Ophthalmology Task Force · Recommendations for Genetic Testing of Inherited Eye Diseases (2014) · www.aao.org
6. European Medicines Agency · Luxturna (voretigene neparvovec) EPAR · www.ema.europa.eu
7. US Food and Drug Administration · Luxturna · www.fda.gov

By Dr Chan Li Yen. General information only. It does not replace a consultation. If you are worried about your child's eyes or vision, please see an eye doctor.