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The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina. [1] It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil.
The iris consists of two layers: the front pigmented fibrovascular layer known as a stroma and, behind the stroma, pigmented epithelial cells.. The stroma is connected to a sphincter muscle (sphincter pupillae), which contracts the pupil in a circular motion, and a set of dilator muscles (dilator pupillae), which pull the iris radially to enlarge the pupil, pulling it in folds.
When pupils are dilated, it means that they grow larger in size. This can happen for a number of different reasons, including drug use and arousal. 7 reasons why your pupils may be dilated, from ...
Mydriasis is the dilation of the pupil, usually having a non-physiological cause, [3] or sometimes a physiological pupillary response. [4] Non-physiological causes of mydriasis include disease, trauma, or the use of certain types of drug.
Opioids such as fentanyl, morphine, heroin and methadone (the notable exception being pethidine); Products containing nicotine such as cigarettes, chewing tobacco or gum ...
Videos like this have helped the content creator find an audience with young fans, including Cindy Marie Jenkins's two kids, ages 6 and 9. “My kids laugh a lot at watching how long four ...
The irises of human eyes exhibit a wide spectrum of colours. Eye color is a polygenic phenotypic trait determined by two factors: the pigmentation of the eye's iris [1] [2] and the frequency-dependence of the scattering of light by the turbid medium in the stroma of the iris.
Make sure your shoes and clothing fit well and don’t rub your skin, Dr. Lizarzaburu says. “Anything that’s causing friction will put you at risk of developing a blister.”