Iris
It is the colored part of the eye : the iris , also known as the iris. This part of tissue, colored by pigmentation, separates the anterior from the posterior chamber of the eye. The iris regulates the incidence of light, similar to a camera aperture.
Definition
The iris is an organ tissue composed of muscle tissue and pigment (melanin) and plays an important role in vision. The pigments give the eye the color that depends on their concentration. Weak pigmentation makes the eyes appear blue, green, or gray. If they are heavily pigmented, they are brown.
An infant’s eyes are not fully developed at birth, so almost all babies start out with either blue or gray eyes. In the course of the first year of life or even later, the pigmentation develops and the children get their final eye color.
If there is no pigmentation, for example due to albinism, the iris appears red because the dense tissue network becomes visible. The iris uses two muscles to regulate the incidence of light on the retina . A process that happens unconsciously.
Anatomy
The uvea, the middle layer of the eye, is made up of three parts: the choroid (choroid), the corpus ciliare (ciliary body) and the iris (rainbow membrane). The iris is at the front, directly at the transition from the cornea to the white skin of the eye, separating the anterior from the posterior chamber of the eye.
The iris itself is composed of two sheet-like layers and consists of muscle fibers, the epithelial tissue, which is one of the four basic tissues, and a stroma (intermediate tissue), which consists of connective tissue, various cell types , vessels and nerves . On the front of the iris is a layer of mesothelial cells, on the back is a two-layered pigmented tissue. In the center of the iris is the pupil , a visual hole that allows light to enter the eye.
Two muscles, also located in the stroma, ensure that the pupil narrows (in light) or widens (in darkness). The sphincter pupillae muscle lies close to the free edge of the pupil and narrows the pupil. The dilatator pupillae muscle is located at the attached edge of the iris and dilates the pupil. The structure of the stroma is not identical in every human being. Therefore, iris recognition, similar to fingerprints, is used for biometric person recognition.
Function
The iris plays its most important role in regulating the incidence of light. It can adapt dynamically to the lighting conditions and works like the aperture of a camera. The more light that enters, the smaller the aperture and vice versa. The pupil is the central opening for light to enter. Depending on the strength of the light intensity, the two muscles of the iris can regulate the diameter of the pupil in the range of 1.5 to 12 millimeters. Temporary narrowing of the pupil is called miosis, dilation of the pupil is called mydriasis.
The iris muscles cannot be consciously controlled as they are subject to the autonomic nervous system. Dilation of the pupil occurs in the dark, distant vision, pain, cocaine abuse, a migraine attack or stress. With strong brightness, night vision and tiredness, the pupils let less light through. The pupils also narrow when we are tired, when we abuse alcohol or when we abuse morphine.
Diseases
- Heterochromiezyklitis
- Irismelanoma
- albinism
- Aniridia
- Iris-Heterochromie
- iris inflammation
One of the most common forms of inflammation of the iris and the ciliary body is iridocyclitis, which usually occurs together with an internal disease such as herpes simplex, rheumatic diseases, gonococcal infection or Crohn’s disease . However, it also occurs as an independent clinical picture.
The symptoms of iridocyclitis include eye pain, sensitivity to light, color changes in the pupil, poor vision due to clouding of the vitreous body and protein deposits in the cornea. Anti-inflammatory drugs and antibiotics can usually be treated successfully.
A special form, the so-called heterochromic cyclitis, has a good prognosis. It is noticeable through depigmentation of the iris, and patients complain of pain.
The prospects of healing are also good for iris melanoma, which usually does not cause any symptoms. Since this tumor is very easy to recognize in the eye, it can be treated quickly.
Albinism is a special form of visual impairment. Due to the lack of pigmentation, the iris cannot regulate the incidence of light. This leads to glare and impaired development of the visual function even in infancy. The visual disturbance is often combined with a malformation of the retina.
Aniridia is a rare, hereditary condition in which the iris is absent from birth and usually affects both eyes.
Iris heterochromia, in which the irises differ in color, also occurs relatively rarely. This pigmentation disorder can occur in connection with Waardenberg syndrome, a genetic disease. It can also develop after an iris infection. This does not affect vision or field of vision.
Hello and welcome to my Health Guide & Encyclopedia! My name is Dorothy Farrar, and I'm the founder and main author of this platform.
My passion for health and wellness started at a young age when I became interested in the connection between the food we eat and the way we feel. This fascination led me to study nutrition and dietetics in college, where I learned about the importance of a balanced diet and the impact of various nutrients on the body.