macular degeneration

Macular degeneration: description

The retina is a special part of the nervous system that lines most of the inside of the eyeball. It is responsible for converting light stimuli into nerve impulses: The light strikes certain molecules in the photocells of the retina, which generates the nerve impulses. These impulses are in turn directed by the optic nerve to the brain, where they are processed and finally recognized as images.

The retina construction and its function

The retina consists of many layers that are formed by different types of nerve cells. The first link in the processing of light signals to nerve impulses are the light-sensory cells, the so-called cones and rods. They convert the light stimuli and pass them on to other nerve cells, which in turn are connected to other cells. In this way, the signal is transported via several intermediate stations to the optic nerve and from there to the brain.

The light-sensory cells are located in the deepest layer of the retina, so that the light must first pass through all other layers. When the light has arrived there, a certain cell component, the retinal, changes and splits off small parts (“membrane discs”). It is consumed and must be renewed.

Disturbed waste removal

This reprocessing of the photoreceptor cells is the responsibility of the associated retinal pigment epithelium (RPE). It transports the resulting waste products and regenerates the cones and rods.

If this degradation component is damaged, accumulating metabolic products in the retina, for example, the lipofuscin and split membrane discs can no longer be properly removed. They pile up and destroy the RPE first. As a result, the photoreceptor cells also perish and macular degeneration occurs.

What happens with macular degeneration?

Although the macular degeneration is a disease of the retina, it is not the entire retina damaged, but mainly a specific area. The area is called macula lutea or “yellow spot”. This is a roundish, approximately five millimeters large area in the center of the retina, which stands out from its environment by a special density of light sensory cells.

The light-sensory cells of the macula are predominantly cones that allow sharp vision in color. The other group of light-sensing cells (photoreceptors) represent the rods. They are responsible for the black-and-white vision in low light conditions and therefore important above all in dim light or at night. Without the yellow spot, one would not be able to read, recognize faces, and only dimly perceive the environment.

If the macula is destroyed, it results in a massive visual impairment. Since the retina around the yellow spot often remains intact, one does not completely blind in this disease. Accordingly, in the macular degeneration, the edges of the field of view are still perceived, but not what is fixed in the center of the visual field.

Which forms of macular degeneration are there?

A distinction is made between the age-related macular degeneration of those in which gene defects or other factors are the cause. In addition, a distinction is made between wet and dry macular degeneration.

Age-related macular degeneration (AMD)

The most common form is called age-related or age-related macular degeneration. The destruction of the yellow spot rarely begins before the age of 60.

Overall, this disease is the leading cause of blindness in western industrialized countries. In Germany alone, about 4.5 million people are affected. The term “blindness” may be misleading, because even a low vision is maintained. In the later stage of the disease, one can almost speak of blindness.

In poorer countries, age-related macular degeneration is often not the first cause of blindness because of the dominance of other eye diseases that can not be treated adequately due to lack of medical care. Examples are the green star (glaucoma) or infectious diseases like the trachoma.

The dry macular degeneration

75 percent of patients with age-related macular degeneration are known as dry macular degeneration. The insufficiently transported away waste products of the photoreceptors and especially lipofuscin are deposited and form in some places larger associations, which are called “drusen”.

Drusen-induced extensive damage to the retinal pigment epithelium is also known as “geographic atrophy”. As dry macular degeneration progresses slowly, it initially has little effect on vision. However, it can change into a wet macular degeneration at any time.

The wet macular degeneration

The wet macular degeneration (exudative form) is almost always the result of a dry macular degeneration. The pathological deposits in the retina lead to the destruction of the cells of the retinal pigment epithelium and create gaps in the membranes under the retinal layer. In addition, the blood supply is disturbed by the choroid and the retina at the affected sites are no longer sufficiently supplied with oxygen.

Vessels destroy the retina

The body therefore forms certain messenger substances, so-called growth factors, which stimulate the regeneration of small blood vessels. These factors also play an important role in macular degeneration treatment. Their action sprouts small vessels from the choroid. The process is called choroidal neovascularization (CNV).

Although the body thus wants to counteract the oxygen deficiency, the new vessels also grow through the membrane gaps under the retina, where they actually do not belong. As a result, the retina may detach, leading to impaired vision and eventually partial or even total blindness. In addition, the walls of the newly formed vessels are not as stable as the normal blood vessels. Therefore, a little bit of fluid constantly leaks into the environment, which further promotes retinal detachment. This phenomenon also explains the term “wet macular degeneration”. The small vessels can also tear, bleeding into the retina.

The wet macular degeneration is much faster and more dangerous than the dry form. It is estimated that about every seventh dry macular degeneration eventually passes into a damp.

Macular degeneration: symptoms

The macula is the most important area of ​​the retina for seeing, if you fix something sharply, it is only possible through the yellow spot. In the peripheral areas of the visual field, the environment is only dimly perceived. But even the blurred vision of the edges around the macula is important. Only in this way can one orientate oneself in space and register movements around oneself.

Macular degeneration symptoms in the early stages

In early stages of macular degeneration, there is often no noticeable visual impairment. Although in the course of both eyes are usually affected by the disease, but often it first appears only in one eye. This can be compensated for the first sight loss on the diseased eye of the still healthy eye. The person concerned initially does not notice anything of the macular degeneration. For example, symptoms first appear when reading. The middle of the text may appear slightly blurry, distorted, or overlaid by a gray shadow. Often, the macular degeneration in the early stages but a coincidence with the ophthalmologist, especially since it causes no pain.

Macular degeneration symptoms later

The further the macular degeneration progresses, the more pronounced the symptoms become. Especially when both eyes are affected, so the deficits of one can not be compensated by the other eye. In general, the destruction of the yellow spot in the center of the field of vision leads to:

• Decrease in visual acuity
• Decrease in the contrast sensation
• Decrease in color perception
• Disruption of adaptation to changing light and increased photosensitivity
• distorted perception of the environment (metamorphopsia)

Due to the fuzzy perception of the central field of view, differences in brightness of the macula can no longer be detected so well. Contrasts then appear blurred. Because adapting to changing light conditions (adaptation) is also limited, those affected quickly feel dazzled in bright light. Since macular degeneration destroys a large part of the cones in the retina, color vision also suffers. The affected increasingly see only in black and white.

Straight lines appear as waves

The distorted perception (metamorphopsia) is particularly evident when viewing straight lines, such as lattice patterns or tile joints. The straight lines suddenly appear bent or wavy. This is how the macular degeneration test works.

When the macular degeneration is well advanced, the vision in the center of the field of view may be completely lost. At this point the patients only see a bright, gray or black spot. This spot is referred to in ophthalmology as a “central scotoma”.

Macular degeneration: causes and risk factors

Although the mechanism leading to macular degeneration is well known, it is still the subject of research to find out why, especially in old age, the removal of metabolic products in the eye is no longer sufficient. In addition to drugs or inflammation on the eye, there are certain risk factors that can promote macular degeneration. These include:

• A high age
• Toxic influences, for example the drug chloroquine
• Inflammatory processes on the eye due to infectious diseases
• Smoke
• Family bias

In fact, age is the biggest risk factor for macular degeneration. While about one percent of 65-74 year-olds are affected, five percent of those aged 75-84 have an age-related macular degeneration. As society grows older and older in Western industrialized nations, the incidence of macular degeneration is increasing.

Chloroquine is a drug for malaria prophylaxis and treatment of rheumatic arthritis. In some patients treated with it, macular degeneration was noted during the course. These are exceptions.

Smoking also worsens the blood circulation on the eye, so that the retina is not sufficiently supplied with oxygen. In addition, metabolites in the retina are removed by smoking worse. People who consume tobacco for many years increase the risk of developing macular degeneration.

As is the case with many diseases, a familial accumulation can also be detected in the case of macular degeneration. It is thought that a certain gene constellation makes the risk of (age-related) macular degeneration more likely.

Macular degeneration as a result of a genetic defect

If a true genetic defect is the cause, the typical symptoms of macular degeneration already occur in children and adolescents. Examples of such genetic defects are Best’s disease (vitelliform macular degeneration) or Stargardt’s disease. In the case of Stargardt’s disease, the photoreceptors destroy themselves.

Macular degeneration as a result of myopia

In rare cases, severe myopia can lead to macular degeneration. Myopia is usually the result of a too long eyeball. Due to the anatomical imbalance train is exerted on the retina. In the long term, this causes the choroid under the macula to thinn out, so that the blood supply at some point is no longer sufficient. This creates a wet macular degeneration.

Macular degeneration: examinations and diagnosis

Although the symptoms of macular degeneration are typical, they alone are not enough to diagnose. Ultimately, other diseases of the eye can lead to similar symptoms. From the age of 55, patients are entitled to regular check-ups. Thus, age-related macular degeneration can be detected early.

The Amsler grid

The Amsler grid is named after a Swiss ophthalmologist and represents a recorded, fine-meshed grid with a small black dot in the middle. The patient is located half a meter away from the Amsler grid. Now he must aim the point alternately with the right and left eye, whereby the other eye is closed. Affected macular degeneration sees holes or blurred dark spots in the grid. The grids may also appear distorted and wavy.

The Amsler lattice is not a pure macular degeneration test because it indicates all possible damage to the retina. However, the grid is used in many ophthalmological practices, especially in older patients, to detect age-related macular degeneration at an early stage. Since the Amsler grid is also available on the Internet, you can first test yourself if suspected.

Examination of the ocular fundus (ophthalmoscopy)

The inner retina-lined surface of the eyeball is called the ocular fundus. By means of an ophthalmoscope, the doctor can look at the ocular fundus. He looks under illumination through a magnifying glass into the eye. In a macular degeneration, typical structures such as drusen and degenerated thinned tissue often show up, as well as inoculating vessels, exudates and hemorrhages in wet macular degeneration.

In most cases, the ocular fundus is photographed during ophthalmoscopy in order to be able to compare the condition with later pictures.

Fluorescence angiography (FAG)

Fluorescence angiography (FAG) clearly diagnoses macular degeneration. For this, the patient is injected with a special fluorescent dye into a vein, which circulates in the systemic circulation and, among other things, also accumulates in the vessels that supply the retina. If now the fundus is irradiated with short-wave light, the dye lights in the vessels, which can then be assessed. For example, newly formed vessels can be easily recognized in wet macular degeneration.

visual acuity

In order to specify the degree of vision loss objectively, the doctor determines the patient’s visual acuity (visual acuity). A healthy young person has a visual acuity between 1 and 1.6. In older people, it drops to 0.6. However, if there is age-related macular degeneration in the terminal stage, the visual acuity may fall below 0.02.

Macular degeneration: treatment

The procedure for macular degeneration therapy depends on whether it is a wet or dry macular degeneration. Basically, there is no treatment that can counteract the actual cause of the disease. Therefore, the progression of the disease in the long term usually can not be prevented. However, progress can be delayed by medication or certain technical procedures and the quality of life of patients can be increased. To at least initially compensate for the loss of vision, there are special reading glasses and magnifying glasses.

How to treat the dry macular degeneration

Dry macular degeneration focuses on the administration of substances that prevent damage to the retinal pigment epithelium in the macula. Among them are mainly zinc and copper oxide as well as so-called antioxidants such as vitamins C and E, or beta-carotene. Lutein is a substance that also naturally finds itself in the macula and helps to form the macular pigment. Similar to antioxidants, this natural “dye” protects photoreceptors in the retina from damage from short-wave light or free radicals.

In addition, recent studies have shown that the administration of vitamin B6, B12 and folic acid has a positive effect on the course of macular degeneration.

This is how to treat the wet macular degeneration

What makes the wet macular degeneration progress particularly fast is the neovascularization. The treatment options attack here. For example, one tries to destroy the vessels and thereby improve the visual acuity.

In some patients, a laser treatment helps, in which the laser rays erode the pathological vessels. This only works if the vessels are not directly in the macula. Another disadvantage is that in macular degeneration, scars develop in the intact tissue, which in turn can impair vision.

During photodynamic therapy, the doctor injects a non-toxic dye into the arm vein. This accumulates in the pathological vessels and makes them sensitive to low-energy laser light. This systematically destroys the vessels without harming the surrounding tissue.

Another treatment option for macular degeneration are drugs that contain antibodies (pegaptanib and ranibizumab). These drugs interfere with the action of the growth factor VEGF, which stimulates the formation of new vessels. The antibody injects the doctor directly into the vitreous body of the eye.

Surgical procedures, such as subretinal surgery or retinal rotation (retinal rotation) with displacement of the macula, are only in rare cases useful and are still partially in the testing or development.

Therapeutic approaches without guaranteed effectiveness

Through the so-called rheophoresis certain proteins can be removed from the blood. Rheophoresis is similar to dialysis and improves the flow properties of the blood. However, its effectiveness has not been proven.

There are also alternative treatment options for people with macular degeneration: acupuncture, for example, can have positive effects in individual cases, especially in dry macular degeneration.

Overall, one should undergo therapeutic measures that have no proven efficacy and the scientific background is questionable, possibly as a supplement to a proven in their effectiveness therapy method.

Macular degeneration: disease course and prognosis

How a macular degeneration proceeds is very different. As long as there is a dry macular degeneration, the disease usually progresses slowly. Sometimes the disease progress can stagnate completely for a long time. Then the patients do not notice any worsening of the symptoms for months, sometimes years. However, a complete stoppage is very unlikely, although occasionally such cases have been described.

In about 15 percent of the cases, a dry macular degeneration eventually results in a moist. The wet macular degeneration develops very rapidly. If one of the morbid vessels breaks, bleeding into the macula can lead to a sudden severe vision loss. The patients then look considerably worse from one moment to the next.

Since a macular degeneration is not curable so far, one should prevent the disease: This includes avoiding hypertension and obesity. It is especially important not to smoke. A smoking cessation reduces the risk for one macular degeneration in old age.