Important terms from the field of visual aids

Accommodation is the adjustment of the refractive power of the eye (“focusing”), e.g. from a distant object (TV) to a near object (newspaper).

ACHROMATOPSY is a rare genetic disorder that leads to complete color blindness. People with achromatopsia cannot see colors and often have impaired visual acuity and sensitivity to light.

The cause of achromatopsia is a malfunction of the cones in the retina of the eye. Cones are the sensory cells responsible for color vision. In people with achromatopsia, these cones are missing or do not function properly, resulting in an inability to perceive colors.

The symptoms of achromatopsia can vary from person to person, but typically include

• Complete color blindness: affected individuals cannot see colors and see the world in black and white.
• Reduced visual acuity: Visual acuity can be severely impaired, resulting in blurred vision.
• Sensitivity to light: People with achromatopsia are often very sensitive to bright light and therefore need special sunglasses or other protective measures.
• Nystagmus: An uncontrollable shaking or wobbling of the eyes can occur in some people with achromatopsia.

Afocal in optics, the term “afocal” refers to an optical arrangement or system in which the rays enter and exit parallel to the optical axis. In other words, an afocal system has no focal point and does not change the path of the light. Binoculars are an example: the light enters and leaves the binoculars in parallel.

Age-related macular degeneration is an eye disease that leads to a loss of central vision over time. It often occurs in older people and is one of the main causes of visual impairment and blindness in people over the age of 50. Age-related macular degeneration causes damage to the macula, the central area of the retina responsible for sharp vision and recognising details. There are two forms of age-related macular degeneration:

1. Dry age-related macular degeneration: This is the more common form and occurs slowly. Deposits (drusen) form in the macula, which can lead to a gradual deterioration in vision.
2. Wet age-related macular degeneration: This form is rarer but more serious. Abnormal blood vessels grow under the macula, which secrete fluid or blood and can lead to rapid loss of vision.

The symptoms of age-related macular degeneration include blurred or distorted vision in the central field of vision, difficulty reading or recognising faces, problems distinguishing colours and a general deterioration in central vision.

There is no cure for age-related macular degeneration, but there are several treatment options to slow the progression of the disease and alleviate symptoms. These include medication to treat wet age-related macular degeneration, laser therapy and special visual aids such as magnifying glasses or magnifying spectacles.

It is also important to have regular eye examinations to detect age-related macular degeneration early and take appropriate action. In addition, certain lifestyle changes such as a healthy diet, smoking cessation and protecting the eyes from UV radiation can help to reduce the risk of developing or progressing age-related macular degeneration.

Amaurosis fugax is a medical term that describes a temporary visual impairment. It is a sudden and temporary loss of vision in one or both eyes, usually lasting only a few minutes. The term ‘amaurosis’ refers to complete blindness, while ‘fugax’ means that the symptoms are temporary.

Amotio retinae, also known as retinal detachment, is a medical condition in which the retina detaches from the underlying layer of tissue. The retina is the light-sensitive tissue at the back of the eye that is responsible for converting light into electrical signals that are then transmitted to the brain.

Aniridia is a rare congenital eye disorder in which the iris (iris) of the eye is partially or completely missing. The iris is the coloured part of the eye that surrounds the pupil and narrows or widens depending on the amount of light entering the eye.

In people with aniridia, the iris is either absent or only present in a rudimentary form. This leads to various problems related to vision and other eye functions. The most common characteristics of aniridia include:

1. Reduced visual acuity: As the iris normally helps to control and focus incoming light, its absence can lead to reduced visual acuity. People with aniridia often have difficulty recognising details and seeing in bright light.
2. Sensitivity to glare: Without a normal iris, people with aniridia may be more sensitive to bright light. This can lead to glare and discomfort.
3. Nystagmus: Many people with aniridia also have nystagmus, an uncontrolled rhythmic movement of the eyes. This can further impair vision.
4. Malformations of other eye structures: In some people with aniridia, other parts of the eye may also be affected, such as the lens or the optic nerve.

It can either occur in isolation or be part of a syndrome associated with other physical or mental developmental disorders. Genetic mutations are thought to be responsible for the development of aniridia, but the exact cause is not yet fully understood.

There is no cure for aniridia, but there are several treatment options to alleviate symptoms and improve vision. These include wearing sunglasses or special contact lenses to reduce glare, using magnifying vision aids and participating in vision therapy programmes to maximise vision.

People with aniridia should have regular eye examinations to recognise potential complications early and take appropriate action. Working closely with an ophthalmologist or rare eye disease specialist is important to receive appropriate care and support.

Aniseikonia is an eye disorder in which the two eyes perceive different image sizes. This means that the image projected on the retina of one eye is larger or smaller than the image on the retina of the other eye. This can lead to a distorted perception of size and depth.

The causes of aniseikonia can be varied. One common cause is a difference in refractive power between the two eyes, which leads to a different magnification or reduction of the image. This can be caused by an unequal length of the eyeball, a different curvature of the cornea or a different refractive power of the lens.

Another possible cause of aniseikonia is a one-sided visual impairment or strabismus, in which one of the eyes cannot focus properly on the object. This results in a difference in image size between the two eyes.

The symptoms of aniseikonia can vary, depending on the severity and extent of the disorder. Possible symptoms include blurred vision, difficulty with spatial vision and activities that require accurate perception of size, such as reaching for objects.

Treatment for aniseikonia aims to equalise image size in both eyes to allow normal perception. This can be achieved through the use of special glasses or contact lenses that enlarge or reduce the image in one eye to match the other eye. In some cases, refractive surgery may also be considered to equalise the refractive power of the eyes.

It is important to recognise and treat aniseikonia at an early stage, as it can affect vision and quality of life. Regular ophthalmological examinations are therefore recommended, especially for children, who are more prone to aniseikonia. An ophthalmologist can make an accurate diagnosis and recommend appropriate treatment options, and it is important to recognise and treat aniseikonia early as it can affect vision and quality of life. Regular ophthalmological examinations are therefore recommended, especially for children, who are more prone to aniseikonia. An ophthalmologist can make an accurate diagnosis and recommend suitable treatment options.

Anisometropia is an eye disorder in which the two eyes have different refractive powers. This means that one eye has a different visual defect (refractive error) than the other eye. The most common forms of anisometropia are anisometropic myopia (a form of short-sightedness), anisometropic hyperopia (a form of long-sightedness) and anisometropic astigmatism (a curvature of the cornea).

The causes of anisometropia can be varied. One possible cause is a difference in the length of the eyeball between the two eyes, which leads to a difference in refractive power. This can be genetic or caused by environmental factors such as unequal visual exposure during childhood.

Anisometropia can lead to various visual problems. As each eye perceives a different image, this can lead to blurred vision, double vision or a distorted perception of size and depth. People with anisometropia may also have difficulty focussing their eyes properly on objects or even experience problems with spatial vision.

The treatment of anisometropia aims to equalise the refractive power in both eyes and thus enable normal visual perception. This can be achieved through the use of glasses or contact lenses that correct the refractive error in one eye to match the other eye. In some cases, refractive surgery may also be considered to equalise the refractive power of the eyes.

It is important to recognise and treat anisometropia early, especially in children, as it can affect vision and visual development. Regular ophthalmological examinations are therefore recommended to diagnose anisometropia and discuss suitable treatment options. Early treatment can help to minimise visual problems and promote normal visual development.

Aphakia is a medical term used to describe the condition where a person has no natural lens in their eye. This can either be congenital or have been removed by surgery. The lens in the eye is normally responsible for focussing light to create clear images on the retina. With aphakia, this ability is missing, which can lead to severely impaired vision. To improve vision, special contact lenses or spectacles can be used to mimic the function of the natural lens. In some cases, an artificial lens can also be implanted in the eye.

Aqueous humour - fluid inside the eye.

Asthenopic complaints refer to symptoms that occur in connection with overexertion of the eyes. These symptoms can occur when the eyes are subjected to excessive strain, for example due to prolonged work at the computer, reading or other activities that require intensive use of the eyes.

Typical asthenopic complaints include:

Eye fatigue: Eyes feel tired and heavy.

• Dryness of the eyes: Eyes may be dry and irritated, resulting in a burning or scratching sensation.
• Blurred vision: Vision may be temporarily blurred or hazy.
• Headaches: Strained eyes can lead to headaches, especially in the forehead or back of the head.
• Sensitivity to light: Eyes may be more sensitive to bright light than usual.

The following measures can be helpful in alleviating asthenopic complaints:

• Take regular breaks and relax your eyes.
• Light the workplace well and position the screen at an appropriate distance.
• Blink regularly to maintain moisture in the eyes.
• If necessary, use special screen glasses or anti-glare filters.
• Carry out regular eye exercises to strengthen the eye muscles.
• If symptoms persist, consult an ophthalmologist to rule out possible underlying problems and discuss further treatment options.

Carotid artery stenosis refers to a narrowing or blockage of the carotid artery, which carries blood to the brain. This narrowing usually occurs due to deposits of fat, cholesterol and other substances on the inner walls of the artery, leading to the formation of plaques.

Cataracta senilis, also known as senile cataract, is an eye condition in which the natural lens of the eye becomes cloudy. This condition usually occurs in advanced age and is one of the most common causes of vision loss in older people.

The lens of the eye is normally clear and allows light to reach the retina and produce clear images. However, in cataracta senilis, parts of the lens darken and impair the eye's ability to focus light properly. This leads to blurred vision, reduced colour perception and increased sensitivity to glare.

The exact cause of cataracta senilis is not fully understood, but it is thought that various factors such as ageing, genetic predisposition, chronic sun exposure, smoking and certain medications may contribute.

The ciliary body consists of ciliary muscles that can contract or relax with the help of nerve impulses. These muscles are connected to the zonular fibers that extend around the lens. When the ciliary muscles contract, the zonular fibers relax, allowing the lens to curve and increase its refractive power. This process is called accommodation and allows the eye to see objects at different distances in focus.

Colour vision deficiency, also known as colour blindness, is a visual disorder in which a person has difficulty recognising or distinguishing between certain colours. There are different types of colour vision deficiency, but the most common form affects the ability to distinguish between red and green.

People with colour vision deficiency often have difficulty recognising or distinguishing between certain hues. For example, they may confuse red and green or have difficulty distinguishing between different shades of red or green. In some cases, colour vision deficiency can be so pronounced that only shades of grey are perceived.

Comfort filter is an optical filter designed to improve the visual experience and increase visual comfort. It is used to block or reduce certain types of light or radiation that can be perceived as disturbing or uncomfortable. Comfort filters are often used in spectacle lenses to alleviate various problems associated with vision.

Cone dystrophy is a group of hereditary eye diseases that lead to progressive damage to the cones in the retina. This disease mainly affects the function of the cones and impairs colour vision, visual acuity and central vision.

Cones are cells in the retina of the eye that are responsible for colour vision and daylight vision. They are one of the two main types of photoreceptors in the retina, alongside the rods.

The cornea is the transparent, curved structure at the front of the eye. It plays an important role in the refraction of light and thus enables sharp vision. The cornea consists of several layers of cells and has no blood vessels, which keeps it clear.

The main functions of the cornea are to focus the incoming light onto the retina and to protect the eye from external influences such as dust, dirt and bacteria. It is also responsible for transferring nutrients to the lens and other parts of the eye.

Hyperevaporative dry eye is a form of dry eye in which the evaporation of tear fluid is increased due to a disturbed lipid layer of the tear film. The tear film consists of three layers: an outer lipid layer, a middle aqueous layer and an inner mucous layer. The lipid layer forms a protective film on the surface of the tear film and prevents excessive evaporation.

Diabetic retinopathy is an eye disease that occurs as a complication of diabetes. It is caused by damage to the blood vessels of the retina of the eye due to high blood sugar levels. Symptoms can include visual disturbances, blurred vision, dark spots in the field of vision and even blindness.

Diabetic retinopathy can occur in two main forms: non-proliferative retinopathy, where the blood vessels leak and fluid leaks into the retina, and proliferative retinopathy, where new but weak blood vessels grow and can burst easily.

Dioptre is a unit of measurement used in optics to measure the strength of spectacle lenses or contact lenses. It indicates how strongly the lens focuses or scatters the light. The higher the dioptric power, the greater the correction for short-sightedness or long-sightedness.

In the case of short-sightedness (myopia), spectacle lenses or contact lenses have a negative dioptric value, as they diverge the incident light in order to focus it on the retina. In the case of long-sightedness (hyperopia), spectacle lenses or contact lenses have a positive dioptric value, as they converge the incident light in order to focus it on the retina.

Dry macular degeneration, also known as age-related macular degeneration (AMD)

Dry macular degeneration is characterised by a gradual accumulation of yellow deposits, known as drusen, in the macula. These drusen consist of deposited metabolic products and can impair the function of the light-sensitive cells in the macula.

Edge filter is an optical filter specifically designed to block or absorb certain wavelengths of light. It is used to reduce unwanted reflections or stray light and improve the contrast ratio in an image.

Fovea - centre of the macula.

Glaucoma is an eye disease in which the pressure inside the eye is increased and damages the optic nerve. This can lead to a gradual loss of peripheral vision and even blindness if left untreated.

There are different types of glaucoma, but the most common form is primary open-angle glaucoma. In this form of glaucoma, the outflow of aqueous humour from the eye is obstructed, leading to an increase in intraocular pressure. The increased pressure gradually damages the optic nerve and impairs vision.

Hyperevaporative dry eye - the lipid layer of the tear film is impaired, which leads to increased evaporation of the tear fluid. This can have various causes, such as a disorder of the meibomian glands, which are responsible for the production of the lipid layer. Blockage or inflammation of these glands can lead to a lack of lipids and thus to a disturbed lipid layer.

An intraocular lens is an artificial lens that is usually inserted into the eye after cataract surgery to allow the patient to see as normally as possible.

Intraocular pressure, also known as intraocular pressure (IOP), refers to the pressure within the eye. IOP is regulated by the production and drainage of aqueous humour in the eye. A normal intraocular pressure is usually between 10 and 21 mmHg (millimetres of mercury).

Intraocular pressure refers to the pressure inside the eye, more specifically in the anterior part of the eye, which is filled with aqueous humour. IOP is important for maintaining the shape of the eyeball and plays a role in nourishing the tissues in the eye.

The IOP is regulated by the flow of fluid in the eye. The aqueous humour is produced by the ciliary body and then flows through the pupil into the anterior chamber of the eye. From there it is drained through the trabecular meshwork canal, which is located between the iris and the cornea. If the outflow of aqueous humour is impeded or production is increased, the IOP can rise. A normal IOP is in the range of around 10 to 21 mmHg (millimetres of mercury). Elevated IOP, also known as elevated intraocular pressure, can be a risk factor for various eye diseases, especially glaucoma. A high IOP can damage the optic nerve and lead to a gradual loss of vision.

Juvenile macular degeneration is a rare hereditary eye disease that usually occurs in childhood or adolescence. It affects the macula, the central part of the retina, which is responsible for sharp vision and recognising details.

Light requirement is the amount of light needed to fulfil a specific task or function. The light requirement can vary depending on the application and optical system. The more light required for certain tasks, the less magnification is needed.

The lipid layer is the uppermost layer of the tear film, whose main task is to prevent evaporation of the underlying aqueous layer.

The macula is an area in the centre of the retina of the eye that is responsible for sharp vision. It is about 5 mm in diameter and contains a high concentration of photoreceptors, especially cones. The cones are specialised sensory cells responsible for colour vision and daylight vision. The macula is particularly important for activities such as reading, writing, driving and recognising details. It enables us to recognise fine details and see sharp images. In the centre of the macula is a small depression called the fovea centralis, which is the sharpest point of vision.

Macula lutea Yellow spot, point of sharpest vision in which only the cones are active.

Macular degeneration (AMD) see Age-related macular degeneration

Magnifying visual aids are optical aids that help people with visual impairments to magnify objects or texts and thus see better. These aids are often used by people with age-related macular degeneration, glaucoma, diabetic retinopathy or other eye diseases that lead to a loss of visual acuity.

The meibomian glands are special sebaceous glands located at the edge of the eyelid. They produce an oily substance called meibum, which is an important component of the lipid layer of the tear film.

The meibomian glands have several functions:

1. Production of meibum: The glands continuously produce meibum, an oily substance rich in lipids. The meibum is released into the tear film where it forms the lipid layer. This layer prevents evaporation of the aqueous part of the tear film and helps to retain moisture on the surface of the eye.
2. Stabilisation of the tear film: The meibomian glands play an important role in stabilising the tear film. The production of meibum reduces the surface tension of the tear film, helping it to spread evenly over the surface of the eye and form a smooth surface.
3. Protection against irritants: Meibum produced by the meibomian glands also forms a physical barrier against foreign bodies, dust particles and other irritating substances. It helps to protect the eye from external influences.

Metamorphopsia - straight lines are seen distorted.

Night blindness - also known as nyctalopia, is a visual disorder in which a person has difficulty seeing in poorly lit or dark environments. People with night blindness may have reduced vision or complete blindness in dimly lit situations, making it difficult to orientate or perform tasks at night.

Nystagmus is an eye movement disorder in which the eyes make uncontrollable, rhythmic movements. These movements can be horizontal, vertical or rotating and can change from side to side. Nystagmus can be congenital or develop over the course of a lifetime.

Ocular albinism is a genetic disorder that affects the eye. It is a rare form of albinism in which the production or transport of melanin in the eyes is impaired. Melanin is a pigment that is responsible for the colouring of skin, hair and eyes.

People with ocular albinism usually have light skin and hair and a light iris colour. The eyes may also be more sensitive to light than in people without albinism.

The optic canal, also known as the optic tract or optic nerve canal, is a tunnel in the skull bone through which the optic nerve (Nervus opticus) runs. The optic nerve unfolds at the base of the skull and allows the optic nerve to pass from the eye to the brain.

The optic nerve consists of many nerve fibres that transmit information from the eye to the brain. This information is then processed in the brain and represented as visual perception.

Ora serrata is an anatomical structure in the eye that marks the transition between the retina (the seeing part of the eye) and the non-seeing part of the eye (ciliary body). The ora serrata plays an important role in attaching the retina to the surrounding structures of the eye.

Papilla - Blind spot, also known as a physiological scotoma, is an area on the retina of the eye where there are no light receptors. This area is caused by the optic nerve leaving the eye.

Photopic vision refers to vision in daylight or in well-lit environments. It is the state of vision in which the cones in the retina of the eye are primarily responsible for the perception of light and colour.

The cones are specialised photoreceptors in the retina that are sensitive to different wavelengths of light and enable us to see colours. They are particularly active in bright light and provide high resolution and detail.

Presbyopia - age-related visual impairment that usually occurs from middle age onwards. It is a natural change in the lens of the eye and its ability to focus on near objects. In young people, the lens of the eye can change shape to adjust focus between near and far objects. This process is called accommodation. However, as we age, the lens loses elasticity and flexibility, making it more difficult to maintain focus on near objects.

Prismatic effect refers to the ability of a prism to deflect and refract light rays. A prism is a transparent material with a triangular shape that is used in optics to manipulate light. The prismatic effect has various applications in optics. It can be used in spectacle lenses to correct visual defects such as strabismus or double vision. By using prismatic lenses, the light rays can be refracted so that they are focussed on one point again and allow clear vision.

Progressive myopia, also known as progressive short-sightedness, is a form of short-sightedness in which visual acuity deteriorates over time. In contrast to normal myopia, where the visual acuity remains stable or changes only slowly, progressive myopia increases continuously.

Refraction - measurement of eye strength (eye glass determination).

The retina is a layer of specialised nerve cells at the back of the eye. It is responsible for converting light into electrical signals, which are then transmitted to the brain to generate visual information. The retina consists of several layers of cells, including photoreceptors (rods and cones), bipolar cells, ganglion cells and various other supporting cells. The photoreceptors are responsible for receiving light and converting it into electrical signals. The rods are more sensitive in dim light and enable twilight vision, while the cones are responsible for colour vision and vision in bright light. The electrical signals are transmitted from the photoreceptors to the bipolar cells and then to the ganglion cells, whose axons form the optic nerve. The optic nerve transmits these signals to the brain, where they are interpreted and are responsible for visual perception.

Retinal detachment (amotio retinae) is a medical emergency in which the light-sensitive layer of the eye, the retina, detaches from the underlying tissue layer. This can lead to sudden loss of vision and requires immediate medical treatment. Symptoms of retinal detachment may include sudden loss of vision or the appearance of ‘floating’ spots or a curtain sensation in the field of vision. It is important to see an ophthalmologist immediately if retinal detachment is suspected, as early diagnosis and treatment offer the best chance of vision recovery.

Retinopathia pigmentosa (RP) is a hereditary eye disease that affects the retina. It is characterised by the gradual loss of photoreceptors (rods and cones), which leads to a progressive deterioration in vision. In RP, problems with night vision usually occur first, as the rod cells, which are responsible for seeing in dim light, are most severely affected. As the disease progresses, day vision can also deteriorate if the cone cells are affected. Symptoms of retinopathy pigmentosa can vary, but often include night blindness, reduced peripheral vision (tunnel vision), sensitivity to glare and gradual loss of central vision. In some cases, other eye problems such as cataracts or glaucoma may also occur.

Rods are specialised sensory cells in the retina of the eye that are responsible for seeing in dim light and perceiving contrasts. They are one of the two main types of photoreceptors in the retina, alongside the cones.

Scotomas - areas in the field of vision in which vision is restricted or completely extinguished. They can be perceived as blind spots or dark areas and can occur both centrally and peripherally in the field of vision.

Sooty rain - Sudden appearance of red-black spots in front of the eyes.

Subretinal haemorrhage - haemorrhage of vascular clots under the retina, leading to detachment of the retina.

Tonometry - procedure for measuring intraocular pressure, i.e. the pressure within the eye. Intraocular pressure is important as increased pressure on the optic nerve and retina can be harmful and can lead to diseases such as glaucoma.

UV-blocking lenses are spectacle lenses that are able to block or absorb ultraviolet (UV) rays. UV rays are a form of electromagnetic radiation emitted by the sun and are invisible to the human eye but very harmful.

Visual acuity refers to a person's visual acuity or ability to recognise details and contours of objects. Visual acuity is often measured using an eye test and expressed as a series of numbers, e.g. 6/6. The first number in the visual acuity indicates the distance at which a person can see a particular object clearly. In many countries, a distance of 6 metres is used. The second number indicates how far away a person with normal vision would have to be from this object in order to see it as clearly as the person being tested. It is important to note that visual acuity is only a measure of visual acuity and does not take into account all aspects of vision. Other factors such as contrast sensitivity, colour vision and peripheral vision may also play a role and should be considered when assessing the overall picture of vision.

Wet macular degeneration is an eye disease that causes damage to the macula, the central area of the retina responsible for sharp vision. In contrast to dry macular degeneration, which is more common, the wet form is less common but usually more severe.wet AMD causes abnormal blood vessels to form under the retina, which leak and leak fluid or blood into the macular area. This leads to tissue damage and loss of central vision. The exact cause of the development of these abnormal blood vessels is not fully understood, but it is thought that inflammation and genetic factors may play a role.