Night blindness is caused by impaired vision in dim light or darkness. The symptoms sometimes lead to serious restrictions in everyday life. What signs are typical, what tests are used to detect night blindness and what helps?
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Quick overview: Frequently asked questions and answers
What are the signs of night blindness? With night blindness, the eye is unable to adapt to darkness. Those affected have difficulty seeing in poor lighting conditions. How severe the visual impairment is can vary greatly.
What is the reason for night blindness? The visual impairment can be congenital. Sometimes the cause is a vitamin A deficiency or an underlying disease such as retinitis pigmentosa or diabetes mellitus.
How is night blindness treated? Congenital night blindness cannot be treated. If other underlying diseases lead to poor eyesight, they must be treated.
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What is night blindness?
Night blindness (hemeralopia) is the limited ability to see in dim light or darkness. It is caused by defective or missing cells in the retina (rods). Rods are receptors that mediate black and white vision.
If these cells are impaired, the retina’s adaptation reaction to the dark (dark adaptation) is disrupted or not possible. This visual impairment can be acquired or inherited. Experts refer to the latter as congenital stationary night blindness (CSNB).
Daytime vision is normal with night blindness, provided there are no other eye diseases.
Various disturbances in night vision are possible
While congenital hemeralopia is rare, so-called night myopia is more common. The term twilight vision is also common.
The eye becomes slightly short-sighted in the dark or existing short-sightedness becomes worse. The reason is that the pupils dilate at night. As a result, poor eyesight has a greater impact on visual acuity.
Night myopia is often noticeable when driving at night. For those affected, glasses can be useful for night driving.
Various eye diseases also lead to, among other things, limited night vision. For example, cataracts, which are associated with clouding of the lens. Experts speak of reduced contrast vision in this regard.
Symptoms: This is how night blindness becomes noticeable
While people with healthy eyes still have relatively good visual acuity in low brightness, a person with night blindness can only see outlines or nothing at all.
In dim light, orientation and the recognition of objects or people are severely limited or impossible. Small obstacles can therefore become a problem – the night-blind person moves unsteadily not only in the dark, but also at dusk.
This has serious consequences for everyday life. For example, driving at night is difficult or impossible due to limited visibility. During the day, however, visual acuity, color vision and field of vision are not restricted – provided there are no other eye diseases other than night blindness.
Causes of night blindness
The visual sensory cells, the so-called cones and rods, are located in the retina of the eye. The approximately seven million cones are used for color vision, daytime vision and sharp vision. The approximately 120 million rods, on the other hand, are responsible for night and twilight vision. They cannot recognize colors.
Through the interaction between cones and rod cells, the eye adapts to the respective lighting conditions. If rod function decreases or fails completely, daytime vision is initially unaffected. However, vision at dusk or at night is impaired.
Eye diseases are often the cause of night blindness
One of the main causes are diseases of the retinal edge. This includes, for example, the hereditary eye disease retinitis pigmentosa (retinopathy). It is one of the most common degenerative retinal diseases that affects both eyes and often leads to night blindness in childhood.
This is often the case if the child has inherited a defective gene from the father and mother. If there is only one defective gene, the eye disease does not appear until the third decade of life. The rods gradually die off, and later also the cones, resulting in a severe restriction of the field of vision and a significant reduction in visual acuity. In extreme cases, blindness can occur.
Vitamin A deficiency can cause night blindness
Other possible causes of night blindness include:
Vitamin A deficiency: Too little intake of vitamin A in food (e.g. in developing countries) can promote poor eyesight. Vitamin A is needed so that the molecule rhodopsin (visual purple), which is important for the visual process, can regenerate from the vitamin A derivative retinal and the protein opsin. In industrialized countries, vitamin A deficiency is relatively rare.
Green Star: The optic nerve is damaged by increased intraocular pressure or an oversensitive optic nerve. This leads to visual field restrictions and also damages the rods.
myopia: Night blindness can also occur as a result of severe nearsightedness (myopia) when this causes retinal tears and holes.
Chorioretinitis: Another cause of night blindness is chorioretinitis. The retina is nourished by the vascular-rich choroid. If the choroid is inflamed, the inflammation can spread to the retina. There is a great risk that the sensory cells will be destroyed. Inflammation of the choroid can occur as a result of various diseases, for example Lyme disease, toxoplasmosis or sarcoidosis.
Retinal changes as a result of vascular damage or blood sugar disease (diabetes mellitus) and lack of oxygen can also severely impair the function of the rods.
Intestinal absorption disorders or zinc deficiency in liver cirrhosis can also result in night blindness.
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Diagnosis: What tests are used to determine night blindness?
Anyone who has poorer vision in certain situations or suspects hemeralopia should visit an ophthalmologist. In general, possible eye diseases should always be clarified promptly.
A series of tests are performed to diagnose hemeralopia. For example, a so-called Goldmann-Weekers adaptometer is used. The test shows the light/dark adaptation of the eyes. First, the patient looks into a brightly lit field in the adaptometer. Then the light is turned off. The perception of brightness for a light source is measured at short intervals.
Another way to diagnose is with the nyctometer. Beforehand, those affected stay in a dark room for ten to 15 minutes so that their eyes can adjust to the darkness. The person is then shown various optotypes. The brightness of the surroundings and the contrast to the surroundings vary.
From the information provided by the patient, the ophthalmologist can determine the degree of night blindness. This test can also be used to determine your ability to drive at night.
Therapy: How can night blindness be treated?
There is no specific treatment for congenital night blindness. If there are other underlying diseases, these must be treated specifically.
In the case of diabetes mellitus, laser treatment can improve the oxygen supply to the sensory cells. Using lasers, it is also possible to improve the outflow of aqueous humor in cases of increased intraocular pressure (glaucoma). Alternatively, the intraocular pressure can be lowered using surgery or eye drops. Laser surgery also repairs retinal tears and holes, while conventional surgery repairs retinal detachments.
There is currently no treatment for retinitis pigmentosa. For some sufferers, nutritional supplements can have a beneficial effect on the course of the disease.
Night blindness: Prevention with an eye check
There is no targeted prevention of night blindness. It is important to visit the ophthalmologist regularly – and at Vision problems immediately – so that any changes in the eyes can be seen.
An eye check will also reveal any increased intraocular pressure or damage to the optic nerve. The intraocular pressure can then be lowered with eye drops or surgery to prevent further damage to the optic nerve. If retinitis pigmentosa runs in the family, genetic testing can be used to determine whether there is a risk of night blindness.
In order to avoid diabetic retinal disease, care should be taken to maintain well-controlled blood sugar levels.
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