Glossary of terms

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Microscopic, free-living protozoa that are relatively common in the natural environment. Although they can cause infections, most people are exposed to acanthamoebae during their lives and do not contract the disease.

Acanthamoeba keratitis
Acanthamoeba can cause several infections in humans, including keratitis, a local infection of the cornea of the eye. This is usually accompanied by severe pain and can result in permanent visual impairment or blindness.

In Ophthalmology, accommodation describes the ability of the eye to change its focus from distant to near objects and vice versa. This process is achieved by the lens changing its shape due to muscle contraction.

Astigmatism is most commonly caused by an irregularly shaped cornea, and in rare cases by the lens of the eye. Vision can be impaired, as the eye does not focus light evenly on the retina. Objects appear stretched and distorted. Mild astigmatism does not affect vision and does not require treatment.

Complete or partial vision loss. Blindness is a very severe impairment of visual acuity and/or visual field. It is defined by law in every country. In Germany, among other things, blindness is defined as having a visual field of less than 5° or a visual acuity of the better corrected eye of no more than 0.02, which roughly corresponds to 2% vision. In the UK, blindness is defined as having a visual acuity of less than 3/60 in the better corrected eye, which roughly corresponds to 0.05 % vision. In the US, someone is legally blind when, among other things, having a visual field of less than 20° or a visual acuity of less than 20/200 in the better corrected eye, which roughly corresponds to 1 % vision.

Contrast sensitivity
Contrast sensitivity is the ability of the retina to perceive differences in brightness.

Small, yellowish deposits that accumulate under the outer layer of the retina due to aging processes or in connection with retinal degenerations. Vision is rarely affected.

Small groups of cells in the vitreous body which cast shadows on the back of the eye (retina), noticed as dark spots or threads. It is common to have floaters that come and go, they are also associated with aging. Floaters may rarely indicate a more serious eye condition, such as a retinal detachment.

A small pit in the retina of the eye where visual acuity is highest (yellow spot or macula). The center of the field of vision is focused in this region where a high number of photoreceptor cells are located.

In Ophthalmology, the fundus is the inner back surface of the eye. The retina and the optic nerve head (optic disc) are located within this inner wall of the eyeball.

The iris is the colored part of the eye. In clinical terms, it is the mobile, ring-shaped structure between the cornea and the lens. The muscles of the iris control the size of the pupil, and thus the amount of light passing through the pupil to the retina.

An inflammation of the cornea. It can have a variety of causes, including bacteria, viruses and fungi. Keratitis is frequently associated with long-term contact lens wear.

Occurs when the cornea thins and gradually bulges outward into a cone-like shape. Keratoconus progresses painlessly and causes distorted vision and deterioration of vision.

Optic disc
Also called the optic nerve head or blind spot. It is the circular area in the back of the inside of the eye, where all retinal nerve fibers exit the eye and form the optic nerve, with blood vessels in the middle, supplying the eye.

Optic nerve
The largest sensory nerve of the eye; transmits sensory impressions in the form of electrical impulses from the retina to the brain.