Amaurosis: Description
The technical term amaurosis (amaurosis) stands for blindness, which is the complete inability to perceive light, in one or both eyes. This corresponds to the scientific definition of blindness.
What does the legislator understand by blindness and visual impairment?
According to the law, blindness is naturally present in all people with amaurosis. However, people are also classified as blind if their visual acuity in the better eye, even with glasses or contact lenses, is less than 0.02 (normal value: 1.0) – i.e. they see less than two percent of what a person with normal vision can perceive.
People whose visual field is less than five degrees are also considered blind by law. The field of vision is the area of the environment that can be seen without moving the head.
Blindness: Frequency
Unlike some other countries, Germany does not centrally record how many people with blindness or visual impairment there are in this country. The World Blind Union (WBU) estimates that there are 253 million blind and visually impaired people worldwide. Based on data from the World Health Organization (WHO), it is estimated that 1.2 million people in Germany are blind or visually impaired.
More precise data is provided by the statistics on severely disabled people: at the end of 2021, 66,245 severely disabled people in this country were blind, 43,015 were severely visually impaired and 225,340 had some other visual impairment.
The incidence of blindness in other regions of the world varies widely. Compared to industrialized countries, blindness is more common in developing countries because of the prevalence of various infectious diseases that threaten eyesight. These include, most notably:
- Onchocerciasis (“river blindness”): a form of filariasis (nematode infection). Second most common cause of blindness worldwide.
Two other diseases leading to amaurosis will be mainly considered below:
- Amaurosis fugax (transient blindness, also temporary blindness).
- Leber’s congenital amaurosis (amaurosis congenita Leber)
Amaurosis: Symptoms
If a patient suffers from amaurosis, he cannot see anything in the affected eye. Depending on the cause of this blindness, various other symptoms may occur.
Symptoms of amaurosis fugax
In amaurosis fugax, someone suddenly goes blind for a few minutes, almost always in one eye only. Pain does not occur. Among other things, this temporary blindness can be the harbinger of a stroke and can be accompanied by other neurological deficits such as sudden hemiplegia.
Symptoms of Leber’s congenital amaurosis
In addition, patients often suffer from involuntary eye tremor (nystagmus), strabismus and farsightedness. Furthermore, Leber`s congenital amaurosis may be associated with cataract (clouding of the eye lens, also called cataract) or keratoconus (protrusion of the cornea of the eye).
Amaurosis: Causes and risk factors
There are various diseases that can underlie amaurosis. Accordingly, the risk factors are also variable. The most common causes of blindness in Europe are as follows:
- Diabetes mellitus (diabetic retinal disease)
- Age-related macular degeneration (loss of the site of sharpest vision on the retina)
- Glaucoma
- Injuries
- Inflammations, e.g. inflammation of the iris (uveitis)
- Retinal detachment (Ablatio retinae)
Apart from these, there are specific causes that can lead to different types of amaurosis. These are described below.
Amaurosis fugax: Causes
Most often, the blood clot originates from carotid artery narrowed by arteriosclerosis: In arteriosclerosis, fat-rich deposits (plaques) form on the inner wall of the vessel. Blood clots can easily form on these plaques, which can break loose and be washed into the central retinal artery with the blood flow. When they clog this or its branches, temporary blindness results in the affected eye. It can be a warning signal for a stroke or a TIA (harbinger of a stroke) – the detached blood clots from the carotid artery can namely also block brain vessels.
Other possible causes of amaurosis fugax include:
- vascular inflammation (vasculitis) such as polyarteritis nodosa (an inflammation of medium-sized arteries) or arteritis temporalis
- connective tissue diseases (collagenoses), especially lupus erythematosus
Risk factors for amaurosis fugax
The most common cause of amaurosis fugax – arteriosclerosis with microembolism in the retina – can be promoted by the following factors, among others:
- Smoking
- High blood pressure
- elevated cholesterol
- overweight or obesity
Leber’s congenital amaurosis: Causes
Amaurosis: examinations and diagnosis
The eye doctor (ophthalmologist) is the right person to talk to if you cannot see in one or both eyes. He first takes your medical history by asking you various questions such as:
- How long has the vision loss been present?
- Are both eyes affected by the vision loss?
- Do the eyes hurt?
- Do you have any known underlying conditions, such as vascular disease?
- Are there any known hereditary diseases in your family?
The doctor then examines your eyes using various methods and devices. For example, he determines the visual acuity of each eye. To do this, you must recognize certain letters or numbers at a given distance on the wall, alternately covering the left and right eye.
Findings in amaurosis
In the case of amaurosis fugax, small, brightly shimmering deposits can often be seen in the vessels of the retina, which block them. To confirm the suspicion of this form of blindness and to detect any impending bottlenecks in the blood supply to the brain in good time, a neurologist and a vascular surgeon should still be consulted. They examine the arteries that supply the brain with blood, firstly with a stethoscope and secondly using ultrasound (sonography). In this way, they can detect possible constrictions.
Other possible causes of acute visual deterioration (e.g., migraine, optic neuritis) must be distinguished from amaurosis due to blood flow.
In Leber’s congenital amaurosis, the ophthalmologist can usually obtain the following findings during the examination in addition to the visual loss:
- nystagmus (eye tremor)
- strabismus (squint)
- no reaction of the pupils to incident light
In the case of this hereditary blindness, a pediatrician should rule out possible other diseases that often occur in addition. These include kidney disease, epilepsy, and mental retardation.
Amaurosis: Treatment
Blindness makes everyday life considerably more difficult. However, with the help of various aids, blind people can find their way in their environment. These include:
- Computer programs that read aloud the information on the screen
- household appliances that communicate with the blind person via sounds, for example when a cooking pot is filled to the brim
- @ a cane for the blind to detect obstacles when walking
In addition, guide dogs can increase safety while walking because they can detect higher obstacles, such as hanging mailboxes, that a guide cane misses.
Therapy for amaurosis fugax
In addition, a healthy lifestyle is of great importance to avoid a possible impending stroke. It includes, but is not limited to:
- abstaining from nicotine
- regular exercise
- good blood sugar control in the case of diabetes mellitus
- lowering blood pressure in case of hypertension
- healthy diet
If an arteritis temporalis is diagnosed as the cause of amaurosis fugax, the patient must be treated immediately with a cortisone preparation. Otherwise permanent blindness is imminent!
Therapy in Leber’s congenital amaurosis
If the congenital blindness is due to a mutation in the RPE65 gene, there is the possibility of gene therapy: In this case, the active substance Voretigen Neparvovec is injected below the retina. This should enable patients to orient themselves better in poor light conditions.
Further therapeutic options (also against other gene mutations) are still the subject of research.
Amaurosis: disease course and prognosis
Leber’s amaurosis congenita is an incurable disease. Affected children are often born blind or go blind during their first year of life. In some cases, a small part of the visual field remains, so that patients can even learn to read with appropriate visual aids.
