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The pupillary light reflex (PLR) or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity of light that falls on the retinal ganglion cells of the retina in the back of the eye, thereby assisting in adaptation of vision to various levels of lightness/darkness.
Pupillary response is a physiological response that varies the size of the pupil, via the optic and oculomotor cranial nerve. A constriction response ( miosis ), [ 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".
The reflex, controlled by the parasympathetic nervous system, involves three responses: pupil constriction, lens accommodation, and convergence. A near object (for example, a computer screen) subtends a large area in the visual field, i.e. the eyes receive light from wide angles. When moving focus from a distant to a near object, the eyes converge.
A mydriatic pupil will remain excessively large even in a bright environment. The excitation of the radial fibres of the iris which increases the pupillary aperture is referred to as a mydriasis. More generally, mydriasis also refers to the natural dilation of pupils, for instance in low light conditions or under sympathetic stimulation.
Scheme showing sympathetic and parasympathetic innervation of the pupil and sites of a lesion in Horner's syndrome. Horner's syndrome is usually acquired as a result of disease, but may also be congenital (inborn, associated with heterochromatic iris) or iatrogenic (caused by medical treatment). In rare cases, Horner's syndrome may be the ...
Adie syndrome [4] is tonic pupil plus absent deep tendon reflexes. Adie syndrome is a fairly common, benign, idiopathic neuropathy that selectively affects the ciliary ganglion and the spinal cord neurons involved in deep tendon reflex arcs. It usually develops in middle age, although it can occur in children.
These fibres are then distributed to deep structures, including the superior tarsal muscle and pupillary dilator muscle. [2] It includes fibres destined for the pupillary dilator muscle as part of a neural circuit regulating pupillary dilatation component of the pupillary reflex. [3] Some fibres of the plexus converge to form the deep petrosal ...