Dilation of pupils - mydriasis – when in daylight or artificial illumination, their diameter is more than 4 mm (that is more than 33 % of the iris diameter), and can be caused by several reasons:
* Paralysis of the pupils sphincter in the injury of parasympathetic pupil innervation (no reaction on light, piloracpine does not have the influence on the diameter of pupil);
* Irritation of sympathetic pupil innervation (spastic option of mydriasis - in so doing the reaction on light still be present);
* Dysfunction of pupils sphincter in case of not working afferent pupillary neurons, and, to the lower extent, mesencephalic internuncial neurons (pilocrpine stimulates constriction of pupils).
The reasons of physiological mydriasis, besides the reasons same to physiological miosis (constitution, age, refraction), can be as follows:
* Sex (the differences take place only in people with light eyes and are not more than 0.25 mm);
* Pain (associated with the increased secretion of adrenaline);
* Emotional (pleasure, fear, irritation, anger, indignation, increased attention, desire etc.);
* Vestibular-pupillary (irritation of vestibular apparatus causes long dilation of pupils after small transient constrictions);
* Cochleo-pupillary;
* Promortal (moment of death and first 2-3 hours after it).
Pathological mydriasis appear under the influence of different etiologic and pathogenetic factors:
* Comatose states (thyrotoxic, epileptic, eclamptic, liver, hypochlorinemic);
* Endocrinopathy (Basedow's disease);
* Severe infectious diseases (botulism);
* Lingering pain syndrome;
* Irritation of meningeal membrane (Flatau symptom);
* Visceral diseases, accompanied by hyperthermia, hypertensive crisis, dyspnea;
* Intoxications (alcohol, narcotic hallucinogen, carbon disulfide, dinitrophenol etc.);
* Pharmacological action (adrenomimetic drugs, anticholinergic novocain et al),
* Hysterical fit (Raedlich's symptom).
Unilateral mydriasis is of interest for topic diagnosis of the central nervous diseases system and is a part of a number of syndromes: Pty's, Notnaghel's, of superior orbital fissure, of external wall of sinus cavernous, Webber's, Benedict's, neuritis of optic nerve and paralysis of oculomotor nerve, post-traumatic encephalopathy.
Diagnosis of unilateral miosis or mydriasis, which is a part of multi-component clinical syndromes, is rather easy. Difficulties take place in differential diagnosis of mono-symptom - isolated unilateral miosis or mydriasis. In such cases pharmacological tests are applied (adrenaline or homatropine).