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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.
The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle [2] of the eye, running radially in the iris and therefore fit as a dilator. The pupillary dilator consists of a spokelike arrangement of modified contractile cells called myoepithelial cells.
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 ...
By analogy with a camera, the pupil is equivalent to aperture, whereas the iris is equivalent to the diaphragm. It may be helpful to consider the Pupillary reflex as an 'Iris' reflex, as the iris sphincter and dilator muscles are what can be seen responding to ambient light. [2] Whereas, the pupil is the passive opening formed by the active iris.
The iris controls the size of the pupil by means of contracting the iris sphincter muscle and/or the iris dilator muscle. The size of the pupils is dependent on many factors (including light, emotional state, cognitive load, arousal, stimulation), and can range from less than 2 mm in diameter, to as large as 9 mm in diameter.
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.
Although the pupillary response, in which the pupil dilates or constricts due to light is not usually called a "reflex", it is still usually considered a part of this topic. Adjustment to close-range vision is known as "the near response", while relaxation of the ciliary muscle to view distant objects is known as the "far response".
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.