News » Pupil: the organ responsible for the transmission of light in constant motion
The pupil is a hole located in the iris center, precisely in front of the eye, whose function is to allow the light to penetrate the back of the eyeball.
It is protected by the cornea, the transparent layer that covers the entire front of the eye.
The size of the pupil can vary from 2 to 5 mm and are not fixed, but variable, since they are directly controlled by the iris that, precisely by means of the pupil, is able to modulate the amount of light that enters the eye: in case weak lighting it tends to expand to allow you to capture as much light as possible (miosis).
This peculiar and subtle activity is regulated by the parasympathetic neurons.
In case of particularly intense light, however, its constriction (mydriasis) allows that the photosensitive cells of the retina are not damaged.
In this case the contraction of the dilator muscles is dall\'ortosimpatico author.
Miosis: the defense of the excess pupil of light and stress
The response of the pupil to fatigue or to bright light stimuli to which it is called in sopposta miosis medical sense, from the greek meiosis (constriction).
This is a reflection of the presence of a light stimulus that is embodied in the decrease of the pupil diameter, which, in this case, rises to strictly physiological episode, however, also observed in certain diseases such as uveitis, the iridocyclitis, as well as in the presence of bodies corneal foreign, eye damage, neurological disorders, narcotic intoxication or chemicals.
Other causes of constriction of the pupil are chemical burns, deep anesthesia, the use of drugs for topical use. Opaque cornea often makes miosis difficult to detect.
Mydriasis: physiological reaction of the pupil to the presence of low light
At the constriction of the pupil, conversely, it also adds the opposite phenomenon, namely the expansion of the same, known as mydriasis, caused by the contraction of the dilator muscle of the iris, as a response, in this case, to an excessive reduction of the light.
Just as the photographer enlarges the aperture of the objective in order to capture light as possible, in the same way mydriasis represents the physiological response of the pupil in deficient light situations. However, this dilation of the pupil can also depend on strong emotions or by the administration of mydriatic drugs. Even some eye disorders or neurological trauma can cause mydriasis, as may be taking medications such as antihistamines, barbiturates, estrogens, tricyclic antidepressants, etc.
Pathologies that affect pupils
Among the diseases that affect the pupils can count anisocoria, an inequality in amplitude of the two pupils who sometimes is genetic in nature, and sometimes of a pathological kind, particularly when the asymmetry is present on the occasion of the stimuli light or the look activities. The anisocoria is also a symptom of other diseases, such as paralysis of the third cranial nerve.
It may depend on the irises congenital defects, trauma, by disruptions pupillary constriction and can also be induced by drugs (eye drops, scopolamine).
The therapy involves various treatments depending on the type of cause that is upstream.
It is therefore appropriate, in the light of what has been reported, see your doctor if there are any changes in size of the pupils, especially if unexplained or sudden, because, as explained, the causes can be the most numerous and diverse.
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