a circular group called the sphincter pupillae, and a radial group called the dilator pupillae. (wikipedia.org)
When the sphincter pupillae contract, the iris decreases or constricts the size of the pupil. (wikipedia.org)
The dilator pupillae, innervated by sympathetic nerves from the superior cervical ganglion, cause the pupil to dilate when they contract. (wikipedia.org)
a circular group set to decrease pupil size on contraction ( sphincter pupillae ). (wikidoc.org)
The dilator pupillae is stimulated through noradrenergic receptors by the sympathetic nervous system . (wikidoc.org)
It consists of loosely arranged collagenous network in which are embedded the sphincter pupillae muscle, dilator pupillae muscle, vessels, nerves, pigment cells and other cells which include lymphocytes, fibroblasts, macrophages and mast cells. (opthametry.com)
Sphincter pupillae muscle forms one millimetre broad circular band in the pupillary part of the iris. (opthametry.com)
Dilator pupillae muscle lies in the posterior part of stroma of the ciliary zone of iris. (opthametry.com)
This layer gives rise to the dilator pupillae muscle. (opthametry.com)
Dilate4
Furthermore, the pupil will dilate if a person sees an object of interest. (wikipedia.org)
When cycloplegic drugs are used as a mydriatic to dilate the pupil, the pupil in the normal eye regains its function when the drugs are metabolized or carried away. (wikidoc.org)
Topical atropine is used as a cycloplegic, to temporarily paralyze accommodation, and as a mydriatic, to dilate the pupils. (the-medical-dictionary.com)
In atropine-induced mydriasis, the mechanism of action involves blocking the contraction of the circular pupillary sphincter muscle (which is normally stimulated by acetylcholine release), thereby allowing the radial pupillary dilator muscle to contract and dilate the pupil. (the-medical-dictionary.com)
Pupillary3
On the inner edge lies a prominent structure, the collarette, marking the junction of the embryonic pupillary membrane covering the embryonic pupil. (wikipedia.org)
In pupillary constriction induced by pilocarpine, not only is the sphincter nerve supply activated but that of the dilator is inhibited. (wikipedia.org)
The size of the pupil is controlled by the action of the pupillary sphincter muscle and dilator muscle. (msdmanuals.com)
Dilation of the pupil3
citation needed] 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. (wikipedia.org)
Some cycloplegic drugs can cause dilation of the pupil for several days. (wikidoc.org)
Regulates the amount of light2
Light enters the eye through the pupil, and the iris regulates the amount of light by controlling the size of the pupil. (wikipedia.org)
In its centre is an aperture of about 4 mm diameter called pupil which regulates the amount of light reaching the retina. (opthametry.com)
Posterior1
Pupil-involving third nerve palsy is considered a neurological as it is most often due to a posterior communicating artery aneurysm compressing the nerve. (nih.gov)
Regulate the amount of light1
The middle portion of the iris has an opening, called the pupil, that helps regulate the amount of light that passes through the retina. (scopeheal.com)
Fibres2
the former, supplied by branches from the oculomotorius nerve, is under control of the will, whilst the dilator fibres belong to the sympathetic system. (yourdictionary.com)
Below this is a circular, and below that again a longitudinal, layer of muscle fibres. (yourdictionary.com)
Contraction1
The reverse is true, so control of pupil size is controlled by differences in contraction intensity of each muscle. (wikipedia.org)
Parasympathetic2
When bright light is shone on the eye, light-sensitive cells in the retina, including rod and cone photoreceptors and melanopsin ganglion cells, will send signals to the oculomotor nerve, specifically the parasympathetic part coming from the Edinger-Westphal nucleus, which terminates on the circular iris sphincter muscle. (wikipedia.org)
The sphincter muscle has a parasympathetic innervation, and the dilator has a sympathetic innervation. (wikipedia.org)
Mydriatic1
All cycloplegics are also mydriatic (pupil dilating) agents and are used as such during eye examination to better visualize the retina . (wikidoc.org)
Dilates2
It is supplied by cervical sympathetic nerves and dilates the pupil. (opthametry.com)
Thus, the pupil dilates and constricts like the aperture of a camera lens as the amount of light in the immediate surroundings changes. (msdmanuals.com)
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. (wikipedia.org)
Light enters the eye through the cornea , the clear, curved layer in front of the iris and pupil. (msdmanuals.com)
After passing through the cornea, light travels through the pupil (the black dot in the middle of the eye). (msdmanuals.com)
Light passing through the cornea is converged (bent) where it passes through the anterior chamber and the pupil, a circular opening regulating the amount of light entering the eye. (medscape.com)
Nerve2
Pupil-sparing third nerve palsy is most often due to an ischemic vascular cause and usually resolves spontaneously in 3 months. (nih.gov)
therefore, the optic nerve must cross through the retina en route to the brain. (wikipedia.org)
Enters the eye1
The iris -the circular, colored area of the eye that surrounds the pupil-controls the amount of light that enters the eye. (msdmanuals.com)
Retina2
The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina. (wikipedia.org)
The pupil changes in size so that the retina receives the optimal light level. (scopeheal.com)
Anterior1
The anterior epithelium and the dilator muscle. (scopeheal.com)
Lens2
It has a contractile diaphragm in front of the lens with a central opening called the pupil. (wikidoc.org)
The iris makes a small circular opening in front of the lens, called the pupil. (scopeheal.com)
Aperture1
In optical terms, the anatomical pupil is the eye's aperture and the iris is the aperture stop. (wikipedia.org)
Prominent1
However, in low-light environments, the pupils will appear much more prominent (or dilated). (scopeheal.com)
Muscle2
The iris is a contractile structure, consisting mainly of smooth muscle, surrounding the pupil. (wikipedia.org)
When this muscle contracts, it reduces the size of the pupil. (wikipedia.org)
Amount of light1
citation needed] The size of the pupil is controlled by the iris, and varies depending on many factors, the most significant being the amount of light in the environment. (wikipedia.org)
Size2
However, in any human age group there is considerable variation in maximal pupil size. (wikipedia.org)
After 25 years of age, the average pupil size decreases, though not at a steady rate. (wikipedia.org)
Bright2
The iris allows more light into the eye (enlarging or dilating the pupil) when the environment is dark and allows less light into the eye (shrinking or constricting the pupil) when the environment is bright. (msdmanuals.com)
This is why, on a bright day, you will notice that the pupils are more constricted. (scopeheal.com)
Vision1
The constriction of the pupil and near vision are closely tied. (wikipedia.org)
Narrow1
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. (wikipedia.org)