page_title: Pupil
section_title: Effect of drugs
hierarchical_section_title: Pupil / Clinical significance / Effect of drugs
caption_attribution_description: English: Pupil of eye dilated with eye drops for retinal examination.
context_page_description: The pupil is a black hole located in the center of the iris of the eye that allows light to strike the retina. 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 term “pupil” was created by Gerard of Cremona.
  In humans, the pupil is round, but its shape varies between species; some cats, reptiles, and foxes have vertical slit pupils, goats have horizontally oriented pupils, and some catfish have annular types. In optical terms, the anatomical pupil is the eye's aperture and the iris is the aperture stop. The image of the pupil as seen from outside the eye is the entrance pupil, which does not exactly correspond to the location and size of the physical pupil because it is magnified by the cornea. On the inner edge lies a prominent structure, the collarette, marking the junction of the embryonic pupillary membrane covering the embryonic pupil.
context_section_description: If the drug pilocarpine is administered, the pupils will constrict and accommodation is increased due to the parasympathetic action on the circular muscle fibers, conversely, atropine will cause paralysis of accommodation (cycloplegia) and dilation of the pupil.
  Certain drugs cause constriction of the pupils, such as opioids. Other drugs, such as atropine, LSD, MDMA, mescaline, psilocybin mushrooms, cocaine and amphetamines may cause pupil dilation.
  The sphincter muscle has a parasympathetic innervation, and the dilator has a sympathetic innervation.  In pupillary constriction induced by pilocarpine, not only is the sphincter nerve supply activated but that of the dilator is inhibited.  The reverse is true, so control of pupil size is controlled by differences in contraction intensity of each muscle.
  Another term for the constriction of the pupil is miosis.  Substances that cause miosis are described as miotic.  Dilation of the pupil is mydriasis.  Dilation can be caused by mydriatic substances such as an eye drop solution containing tropicamide.
caption: Pupil dilated for retina examination
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