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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 drugs .
Pupillary response is a physiological response that varies the size of the pupil between 1.5 mm and 8 mm, [1] via the optic and oculomotor cranial nerve. A constriction response ( miosis ), [ 2 ] is the narrowing of the pupil, which may be caused by scleral buckles or drugs such as opiates / opioids or anti-hypertension medications.
Myosis, pinpoint pupil: ... mydriasis, is the dilation of ... entrainment of the body's circadian rhythms and regulation of the size of the pupil. ...
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 size of the pupil (often measured as diameter) can vary between 8 to 1.5 mm. [4] Pupil size can be a symptom of an underlying disease. Dilation of the pupil is known as mydriasis and contraction as miosis.
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.
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 it encircles the pupil. [2] The pupillary dilation is also called mydriasis, and the constriction of the pupil is also called miosis. [1]
The most common agents used to dilate the pupil are phenylephrine (2.5% in pediatrics or 10% in adults) and tropicamide (0.5% or 1%). While phenylephrine stimulates receptors that contract the dilator muscle of the pupil, [6] tropicamide blocks stimulation of the pupillary sphincter muscle to allow for relaxation. [7]