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  2. Iris (anatomy) - Wikipedia

    en.wikipedia.org/wiki/Iris_(anatomy)

    The iris (brown coloured portion of the eye) controls the size of the pupil by contracting the sphincter pupillae and dilator pupillae muscles. The sphincter pupillae is the opposing muscle of the dilator pupillae. The pupil's diameter, and thus the inner border of the iris, changes size when constricting or dilating.

  3. Iris sphincter muscle - Wikipedia

    en.wikipedia.org/wiki/Iris_sphincter_muscle

    The pupil constricts when the iris sphincter muscle is stimulated and contracts In humans, it functions to constrict the pupil in bright light ( pupillary light reflex ) or during accommodation . [ citation needed ] In lower animals, the muscle cells themselves are photosensitive causing iris action without brain input.

  4. Pupillary response - Wikipedia

    en.wikipedia.org/wiki/Pupillary_response

    Dilation and constriction of the pupil. Pupillary response is a physiological response that varies the size of the pupil, via the optic and oculomotor cranial nerve.. A constriction response (), [1] is the narrowing of the pupil, which may be caused by scleral buckles or drugs such as opiates/opioids or anti-hypertension medications.

  5. Intraocular muscles - Wikipedia

    en.wikipedia.org/wiki/Intraocular_muscles

    The pupillary sphincter muscle and pupillary dilator muscle control the iris to adjust the size of the pupil to adjust how much light enters into the eye. The pupillary dilator muscle increases the pupillary diameter and it is arranged radially, but the pupillary sphincter muscle is responsible for the constriction of the pupil's diameter and ...

  6. Human eye - Wikipedia

    en.wikipedia.org/wiki/Human_eye

    An area termed the limbus connects the cornea and sclera. The iris is the pigmented circular structure concentrically surrounding the centre of the eye, the pupil, which appears to be black. The size of the pupil, which controls the amount of light entering the eye, is adjusted by the iris' dilator and sphincter muscles.

  7. Pupil - Wikipedia

    en.wikipedia.org/wiki/Pupil

    A human adult exhibiting voluntary control over his iris muscles, which grants him the ability to dilate and constrict his pupils on command Pupil dilated naturally to 9 mm due to dim light. The subject is an extreme case, as most individuals are not able to naturally dilate their pupils to that extent Pupil constriction can be in response to ...

  8. Accommodation reflex - Wikipedia

    en.wikipedia.org/wiki/Accommodation_reflex

    Light from a single point of a distant object and light from a single point of a near object being brought to a focus. The accommodation reflex (or accommodation-convergence reflex) is a reflex action of the eye, in response to focusing on a near object, then looking at a distant object (and vice versa), comprising coordinated changes in vergence, lens shape (accommodation) and pupil size.

  9. Iris dilator muscle - Wikipedia

    en.wikipedia.org/wiki/Iris_dilator_muscle

    The pupil widens when the iris dilator muscle is stimulated and contracts. An extreme, though natural, case is shown. The pupillary dilator acts to increase the size of the pupil to allow more light to enter the eye. It works in opposition to the pupillary constrictor. [7]