The pigmented membrane in front of the lens of the eye that acts as a diaphragm to control the amount of light entering the eye through its central opening, the pupil.
A coloured ring in the eye, with the pupil at its centre.
Coloured, muscular ring at the centre of the eye.
Circular, colored part of the eye suspended in the aqueous humor and perforated by the pupil.
A circular tissue of the eye whose color is genetically determined.
The pigmented circular muscle that surrounds the pupil of the eye and controls the amount of light entering it. The iris is made of thin layers of muscle that open or close the dark hole (the pupil) at its center in response to the intensity of surrounding light. In bright light and for near vision, the iris constricts the pupil. In dim light and for more distant vision, it widens (dilates) the pupil. Emotions can also affect the size of the pupil. For instance, the iris widens the pupil in response to fear or danger. The color of the iris, determined by heredity, depends on the amount of pigment cells it contains; blue eyes have less pigment than darker eyes.
The part of the eye that regulates the amount of light that enters. It forms a colored muscular diaphragm across the front of the lens; light enters through a central opening, the pupil. A ring of muscle around the margin contracts in bright light, causing the pupil to become smaller. In dim light a set of radiating muscles contract, increasing the size of the pupil. The outer margin of the iris is attached to the ciliary body.
The opaque, pigmented continuation of the choroid layer of the eye that partly covers the lens, surrounding the pupil and regulating the amount of light that strikes the retina. The iris lies in the aqueous compartment of the eye. It divides the posterior chamber of the aqueous compartment (into which aqueous fluid is secreted) and the anterior chamber (from which aqueous fluid is absorbed). Muscles in the iris can expand or contract the pupil.
The colored disk at the front of the eye, with an opening in its center through which light passes.
The vibrant circular band positioned immediately behind the transparent front layer of the eye, known as the cornea, and situated before the lens, plays a pivotal role in regulating the quantity of luminosity directed towards the delicate membrane lining the inner surface of the eye, referred to as the retina.
The iris is the colored portion of the eye. Located behind the cornea and in front of the lens, it consists of transparent collagen and two sets of muscle fibers, one radial and one circular. The outer edge of the iris connects to the ciliary body. The center of the iris has an opening called the pupil, which allows light to enter the eye and reach the retina. The iris adjusts the size of the pupil to regulate the amount of light that hits the retina.
The color of the iris is inherited from one’s parents and is largely influenced by the amount of melanin, a dark pigment, present in its tissues. Brown eyes have a high concentration of melanin, while blue and grey eyes have minimal melanin; their hue is derived from the collagen tissues. Hazel and green eyes possess moderate melanin levels, with their color originating from both the pigment and the collagen tissues. Specks of color in the iris result from light scattering off blood vessels and muscle tissues. Some individuals, though rare, exhibit two different eye colors, a condition known as heterochromia iridium. People with albinism lack melanin in their bodies, so their eye color is determined by the tissues, resulting in shades of light blue or even pink.