Mydriasis ( ) is pupil dilation, usually having non-physiological causes, or sometimes physiologic pupil responses. Causes of non-physiological mydriasis include illness, trauma, or drug use.
Usually, as part of the light pupil reflex, the pupil dilates in the dark and contracts in the light to each increase the vividity at night and to protect the retina from sun damage during the day. A mydriatic disciple will remain very large even in a bright environment. Excitation of radial fibers from the iris that increases the pupillary aperture is referred to as the midriasis. More generally, midriasis also refers to the natural dilation of the pupil, for example in low light conditions or under sympathetic stimulation.
The informal term for midriasis is pupil burst , and is used by medical providers. Usually it is used to refer to fixed, unilateral, fixed midriasis, which may be a symptom of increased intracranial pressure.
Conversely, narrowing of the pupil, referred to as miosis. Both midriasis and miosis can be physiological. Anisocoria is a condition of one pupil that is wider than the other.
Video Mydriasis
Mekanisme
There are two types of muscles that control the size of the iris: the sphincter slice, composed of circularly regulated muscle fibers, and the iris dilator, composed of muscle fibers arranged radially. The sphincter is innervated by (marked by the nerves) the parasympathetic nervous system, and the dilator by the sympathetic nervous system. The sympathetic stimulation of adrenergic receptors causes radial muscle contraction and subsequent pupillary dilation. In contrast, parasympathetic stimulation causes circular muscle contraction and pupillary narrowing.
The mechanism of midriasis depends on the agent used. It usually involves impaired parasympathetic nerve supply to the eye (which usually constricts the pupil) or overactive sympathetic nervous system (SNS).
The pupil diameter also increases as a reaction to cognitive tasks requiring memory and attention, and this phenomenon is used as an indicator of mental activation ('arousal') in psychophysiological experiments.
Effects
The release of the hormone oxytocin naturally can cause mild to moderate midriasis.
Autonomic neuropathy
The parasympathetic fibers travel with the cranial nerve III, the oculomotor nerve, to infect the circular layer of the eye muscle (sphincter pupillae). This nerve damage usually manifests itself as the midriasis, because the sympathetic supply of the pupil, which causes the midriasis, remains unaffected, and therefore unaffected.
Some central nervous system disorders such as epilepsy, stroke, and brain herniation are known to be known to cause temporal mydriasis as well. Plagues of the brain, or rapidly increasing brain mass, can cause oculomotor nerve compression.
Traumatic
In cases of head injury or orbital trauma (eye injury), the sphincter iris (the muscle responsible for closing the pupil) or the nerves that control it can be damaged, reducing or eliminating the reflexes of normal pupil light.
Drugs
Neurotransmitter norepinephrine regulates many physiological processes in the body and brain, including conscious muscle groups and unconscious muscles of the autonomic nervous system (such as dilation or narrowing of the pupillary hole through the iris muscles).
When intended as a useful effect, various drugs such as Tropicamide are used as an obstruction agent during surgery. Anticholinergics such as atropine, hyoscyamine, and scopolamine are hostile to acetylcholine muscarinic receptors in the eye. By blocking these receptors, the pupils are no longer capable of narrowing and widening (which is essential in eye surgery procedures such as LASIK requiring uninterrupted access to the inner eye through the pupillary opening, requiring the eye to become paralyzed and anesthetized before the procedure can be continued.
Classical stimulant drugs (such as cocaine) serve as a powerful inhibitor of norepinephrine reuptake in the brain (increases the concentration of norepinephrine), with some (especially amphetamines and MDMA) also a norepinephrine release, "liberating" from synapses where it has been sequestered through reuptake. The effect of the newly active norepinephrine torrent is the classic "force push" of the speed users, one of the most widespread characteristics and the unresponsive student, trapped "squeezed open" due to ongoing muscle stimulation. In contrast, opiates such as heroin and morphine operate as large dopamine releasers, which create the opposite effect (depression, not stimulation and miosis, not midriasis). As a hard and fast rule, medical professionals, teachers and police are taught to observe drunk students, with students who "explode" usually indicate amphetamines, cocaine or some "upper" and "pinned" students usually show opiates (such as heroin, oxycodone or some other "downer"). "Archive copy" (PDF) . Archived from the original (PDF) in 2007-09-27 . Retrieved 2007-08-07 . Mydriatics
A mydriatic is an agent that induces dilation of the pupil. Drugs such as tropicamide are used in medicine to allow for retinal examination and other deep eye structures, as well as to reduce painful spinal muscle spasms (see cycloplegia). Phenylephrine (eg Cyclomydril) is used if stronger midriasis is necessary for surgical intervention. One effect of mydriatic administration is the intolerance to bright light (photophobia). Intentionally triggered mydriasis through mydriatics is also used as a diagnostic test for Horner's syndrome.
Maps Mydriasis
See also
- Miosis
- Anisocoria
Note
References
Source of the article : Wikipedia
0 Comments