Night blindness

The phenomenon of night blindness

The signpost on the motorway is illegible and the course of the road can hardly be seen.

Many people suspect they are night blind if their vision is blurred or out of focus in the dark. Even if they come from a light to a dark room and can no longer see anything, many think of night blindness.

However, these symptoms are perfectly normal and do not indicate any illness. Because the human eye first has to adapt to the changed lighting conditions . The rods, sensory cells on the retina, which are responsible for seeing through light and dark, make the eye more sensitive to light. From the age of 50, vision deteriorates in the twilight.

In actual night blindness, however, a serious illness is the cause of the vision problems in the dark. It is difficult to distinguish between illness and the normal process of getting used to the dark. Therefore, people who experience difficulty seeing at night, increased sensitivity to glare, or involuntary eye tremors should definitely see an ophthalmologist .

Night blindness and its symptoms

People who actually suffer from night blindness see very little or nothing at all at dusk and at night . In the night blind, however, the eye loses the ability to adapt to the darkness. Doctors refer to this clinical picture as hemeralopia . In daylight, however, the ability to see is completely intact.

Hemeralopia is due to an eye disease: the rods, sensory cells on the retina that are responsible for seeing through light and dark, no longer function. The reason for the vision problems can be various diseases that primarily occur in the eye or that affect the eye as a symptom. They never only affect one eye, but always both eyes.

Symptoms of Congenital Night Blindness

The congenital hereditary disease retinopathia pigmentosa is usually responsible for night blindness in childhood . Other gene mutations rarely lead to severe night vision problems, for example Oguchi syndrome, the nougaret type, the Riggs type or the Schubert-Bornschein type. These disorders in the genetic material hinder the function of the rods in the eye.

Retinopathia pigmentosa slowly destroys the rods - first at the edge of the field of view, later also in the middle. Other accompanying symptoms of retinopathia pigmentosa are nearsightedness and a restricted field of vision .

In addition to night blindness, affected patients often experience nearsightedness or eye tremors (medically known as nystagmus). If night blindness is caused by the hereditary retinal disease retinopathia pigmentosa, the field of vision gradually shrinks. This means that over time, patients can see an increasingly smaller part of the field of vision.

If a severe vitamin A deficiency is the cause of night blindness, color vision disorders and extremely dry (and therefore watery) eyes often occur at the same time.

Symptoms of acquired night blindness

The later, acquired night blindness in adults can trigger various diseases: a Diabetes mellitus, a gastrointestinal disorder, or liver damage . Night blindness is then the result of these chronic diseases. A vitamin A deficiency can also lead to night blindness, but this is almost non- existent in Europe. In developing countries, however, the low vitamin A level is the reason that an estimated five million children go blind every year.

Since the vitamin A metabolism is directly dependent on the trace element zinc , a severe zinc deficiency can indirectly lead to sudden night blindness. Indeed, the dietary intake of the trace element zinc is often inadequate in Europe, but the deficiency has extremely rare consequences such as night blindness.

Signs of an inherited form are :

• additional myopia
• strong blurring
• Eye tremors (nystagmus)

What are the causes of night blindness?

The sensory cells are located in the retina of a person : around seven million cones are responsible for sharp, day and color vision, and around 120 million rods for night and twilight vision. Both types of sensory cells normally work together so that the eye can adapt to changing light conditions. 

They register the light falling into the eye and convert it into electrical impulses that reach the brain via the optic nerve. If the rods fail, however, vision becomes worse or impossible at night. On the other hand, daytime vision remains unimpaired. Both eyes are almost always affected.

Causes of Congenital Night Blindness

Some babies are night blind from birth. Then an innate (congenital) form is the reason for this, it cannot be treated and remains throughout life. The cause can be mutations in the genome that disrupt the function of the rods, for example the following :

• Oguchi syndrome
• Nougaret type
• Riggs type
• Schubert-Bornschein type
   

Causes of Acquired Night Blindness

If night blindness does not develop until adulthood between the ages of 30 and 50, various diseases that lead to the eye disease can be responsible

Acquired night blindness from diabetes

Diabetics, for example, have a higher risk of night blindness because the metabolic disease can damage the retina and the sensory cells of the retina. In medical jargon, this damage is referred to as diabetic

Retinopathy . It can lead to complete blindness .

Acquired night blindness from vitamin A deficiency

Almost eradicated in Europe - but a great danger in developing countries: Vitamin A deficiency can lead to night blindness and complete blindness. Because the A vitamin is an indispensable component of rhodopsin, the visual purple.

This molecule is made up of the vitamin A derivative retinal and the protein opsin. It is located in the rods and cones and is significantly involved in the visual process. Vitamin A is mainly found in fruits and vegetables such as carrots, broccoli, apricots, peppers, spinach and tomatoes . Since many people in poor developing countries do not have the opportunity to eat enough fruit and vegetables, they lack the important vitamin.

Also liver damage, various gastrointestinal disease and a severe zinc deficiency can vitamin A intake interfere in the body, causing a shortage and thus lead to night blindness. In addition to night blindness, liver damage is accompanied by color vision disorders and pronounced dryness of the eye.

Acquired night blindness as a result of other eye disorders

Diseases directly in the eye also to blame for the poor may be seeing at night: iron deposits in the eye (called siderosis ) or diseases of the optic nerve and the retina, such as a glaucoma (glaucoma).

Diagnosing night blindness

Anyone who notices that they can see worse at night than before should definitely see an ophthalmologist soon. The doctor will ask the patient (or, in the case of small children, his parents) whether night blindness already occurs in the immediate family, i.e. whether there is a family history. If so, it is an indication of the inherited form, retinopathia pigmentosa.

Diagnostics with an electroretinogram

An electroretinogram can help doctors diagnose the congenital disease before symptoms appear. However, the electroretinogram was not specifically developed to detect night blindness. It measures the activity of the retinal cells that receive stimuli, i.e. the rods and cones. The study shows how the sensory cells of the retina react to light stimuli and adapt to the darkness.

Diagnostics through a visual field examination (perimetry)

The patient then usually has a restricted field of vision, which can be determined by a visual field examination (perimetry) . Here the ophthalmologist or optician measures the condition of the field of vision. In a darkened room, the patient looks up at a screen through a type of glasses.

He has to fix a fixed point with his eyes and then recognize and name small, bright points of light at the edge of the field of vision. The doctor determines how far the so-called field of vision extends and in which environment the patient can still perceive light stimuli.

If the congenital form is not to blame for the night blindness, the doctor will ask about other chronic diseases such as diabetes, liver and gastrointestinal diseases .

Diagnostics with an adaptometer

With an adaptometer according to Goldmann-Weekers, the doctor measures how the eye adapts to darkness (so-called dark adaptation examination). The patient looks into a brightly lit field, then the light is switched off. In this way, the doctor can measure the perception of brightness at short intervals.

In addition to night blindness, the doctor can also use the adaptometer to determine the extent of the disorder, namely whether the patient has already developed additional night myopia or increased sensitivity to glare .

Above all, the sensitivity to glare decides whether the patient can and should still drive a car at night - or whether he is no longer fit to drive.

Treatment of night blindness

A possible therapy for night blindness depends crucially on the cause of the impaired twilight and night vision. Treatment must be geared towards this - doctors cannot treat some forms of night blindness at all.

Can you cure night blindness?

There is no cure for the congenital form of night blindness. The doctor cannot completely cure the acquired form of hemeralopia either. However, he can treat the causative diseases, so that the health of the eyes improves and the intensity of the night blindness decreases.

Again and again there are reports that gene therapy could offer treatment approaches: For example, doctors put capsules with genetically modified cells in the eye for the night blind. These cells are supposed to produce the protein CNTF themselves. This is to prevent the cells in the retina from dying off. However, this therapy can only be used preventively - it is not possible to bring dead cells back to life.

Treatment of vitamin A deficiency as a cause of night blindness

If a vitamin A deficiency is to blame for the disease, the vitamin level must be increased. This is possible with a healthy diet rich in vitamins. In addition, however, dietary supplements should be taken. As a preventive measure, it makes sense to strengthen the health of the eyes with a diet rich in vitamin A (especially during pregnancy and breastfeeding). The vitamin is found in fish, meat, eggs. The precursor to vitamin A, beta-carotene, is found mainly in fruits and vegetables, for example in carrots, tomatoes and peppers.

Treatment of other conditions that cause night blindness

Acquired diseases that lead to night blindness can be treated by the ophthalmologist in cooperation with the respective specialist (internist, diabetologist). If this person treats the disease appropriately, night blindness can also improve or its progression can be stopped.

In order to prevent the impending deterioration of vision, diabetics should change their lifestyle and adjust their blood sugar perfectly. If the vision loss progresses, it can be treated with laser therapy. However, there is also the risk that night blindness may develop as a possible side effect, which is why the therapy should be carefully considered

Night blindness surgery

Although the impaired vision caused by a cataract in the medical sense is not night blindness at twilight, it should be mentioned here that a cataract operation can eliminate or at least improve the vision problems caused by the cataract. During the operation, the clouded lens is replaced by a clear artificial lens. This surgery is a common and safe method. The visual difficulties at night can thus be almost completely eliminated.

Treatment of night blindness with low vision aids

Unfortunately, there are no glasses against night blindness, as many sufferers would like. Special glasses, on the other hand, can improve night myopia, which occurs in some people because the pupils dilate in the dark.

In people who are generally already nearsighted, the vision problems can increase at night. The rays of light that enter the eye at the edge of the pupil are refracted more than necessary. Again, this is not night blindness in the medical sense. Additional glasses can correct the vision problem at night.

Consequences of night blindness

Good visibility is an indispensable requirement for participating in road traffic . Driving in the dark is extremely dangerous: Less than a quarter of all journeys in Germany take place at night, but 40 percent of all fatal traffic accidents happen at night. In the case of pedestrians who died, the figure is as high as 72 percent. It is therefore extremely important to have healthy and functioning eyes in order to drive safely.

If the doctor diagnosed congenital or acquired night blindness, the patient is prohibited from driving at dusk and at night. He has to hand in his driver's license. If there is only a so-called glare sensitivity (lights dazzle those affected in the dark, which makes them unsafe when driving) and impaired twilight vision (vision problems at dusk), the patient and the ophthalmologist must decide together whether it is still advisable to drive at night.

Older drivers in particular are then often no longer fit to drive, because sensitivity to glare increases from the age of 50. According to the professional association of ophthalmologists, 11.5 percent between 50 and 59 years of age are no longer fit to drive at night. From the age of 60, the proportion increases to around 20 percent and from 70 even to 35 percent without glare and to 54 percent with dazzling oncoming traffic.