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A limbal ring is a dark ring around the iris of the eye, where the sclera meets the cornea. It is a dark-colored manifestation of the corneal limbus resulting from optical properties of the region. The appearance and visibility of the limbal ring can be negatively affected by a variety of medical conditions concerning the peripheral cornea.
Contents. Iris (anatomy) This article is about the part of the eye. For other uses, see Iris (disambiguation). The iris in humans is the colored (typically brown, blue, or green) area, with the pupil (the circular black spot) in its center, and surrounded by the white sclera.
Green irises, for example, have some yellow and the blue structural color. Brown irises contain more or less melanin. Some eyes have a dark ring around the iris, called a limbal ring. Eye color in non-human animals is regulated differently.
Heterochromia is a variation in coloration most often used to describe color differences of the iris, but can also be applied to color variation of hair or skin. Heterochromia is determined by the production, delivery, and concentration of melanin (a pigment). It may be inherited, or caused by genetic mosaicism, chimerism, disease, or injury.
The corneal limbus manifests as a dark ring around the iris. Its prominence varies by individual. The corneal limbus is the border between the cornea and the sclera. It is highly vascularised. Its stratified squamous epithelium is continuous with the epithelium covering the cornea.
Lisch nodule, also known as iris hamartoma, is a pigmented hamartomatous nodular aggregate of dendritic melanocytes affecting the iris, named after Austrian ophthalmologist Karl Lisch (1907–1999), who first recognized them in 1937.
Brushfield spots are a characteristic feature of the chromosomal disorder Down syndrome or trisomy 21. They occur in 35–78% of newborn infants with Down syndrome. [2] Brushfield spots tend to be obscured by pigmentation of the anterior border layer of the iris in patients with darker irides.
Aniridia is the absence of the iris, a muscular structure that opens and closes the pupil to allow light into the eye. It is also responsible for eye color. Without it, the central eye appears all black. It can be congenital, in which both eyes are usually involved, or caused by a penetrant injury. [1]
A colorful rainbow and ring-billed gull. A rainbow is an optical phenomenon caused by refraction, internal reflection and dispersion of light in water droplets resulting in a continuous spectrum of light appearing in the sky. The rainbow takes the form of a multicoloured circular arc.
Iris is an ambiguous color term, usually referring to shades ranging from blue-violet to violet. However, in certain applications, it has been applied to an even wider array of colors, including pale blue, mauve, pink, and even yellow (the color of the inner part of the iris flower).