Pupil size abnormalities

Dilated pupils (more than 5 mm in diameter) are called mydriasis.

Constricted pupils (less than 2 mm in diameter) are called miosis.

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Bilateral pupillary dilation (mydriasis)

This phenomenon is observed:

1. As a harmless benign feature in vegetatively labile sympathicotonic people.
2. For contact lens wearers.
3. In case of damage to the midbrain.
4. As a result of a disturbance in the reaction to light (often during deep coma).
5. Often with local or internal use of drugs that cause mydriasis (also with hidden use of atropine drugs).

The pupils may dilate with anxiety, fear, pain, hyperthyroidism, cardiac arrest, cerebral anoxia, and sometimes with myopia. The pupils may also dilate with muscular activity, loud sounds, and deep inspiration.

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Bilateral pathological constriction of the pupils (miosis)

Bilateral miosis is observed:

1. As a benign feature (especially in old age) and sometimes with farsightedness.
2. As a normal reaction to bright light in the room where the study is being performed.
3. When the pons and cerebellum are affected, bilateral miosis is observed among other neurological symptoms and is often accompanied by impaired consciousness (the pupils here become very small - “pinpoint”).
4. With local application of drugs (pilocarpine in patients with glaucoma) or internal administration of drugs (morphine derivatives).
5. For syphilis, diabetes, and treatment with levodopa.

Miosis can also occur during sleep, in deep coma, increased intracranial pressure with bilateral involvement of fibers to the m. dilatator.

Difference in pupil size at rest (anisocoria)

Anisocoria indicates either unilateral pathological dilation or unilateral pathological constriction of the pupil.

Unilateral pathologically dilated pupil

Possible reasons:

1. Oculomotor paralysis (accompanied by ptosis and often paralysis of the external eye muscles).
2. Eddie syndrome usually has unilateral or predominantly unilateral manifestations (absence of pupillary light response with preserved convergence response with tonic dilation, often absent tendon reflexes; mainly found in women; usually familial).
3. Unilateral local application of drugs that cause mydriasis.
4. Ciliary ganglionitis.
5. Unilateral damage to the anterior parts of the eye (often accompanied by dilation of blood vessels, deformation of the pupil by synechiae).
6. Unilateral mydriasis in migraine (but also often miosis with Horner's syndrome, especially in cluster headache).

Unilateral pathologically constricted pupil

(possible reasons):

1. Horner's syndrome.
2. Unilateral local application of miotic drugs.
3. Some unilateral local lesions of the anterior chambers of the eye (for example, with a foreign body in the cornea or intraocular).
4. Syphilis (rarely unilateral).
5. For irritation of the third nerve.

"Benign central anisocoria":

The difference in pupil size is rarely more than 1 mm, is more noticeable in poor lighting; the size of the smaller pupil often changes.

Abnormal shape and position of one or both pupils

Shape abnormalities (oval or other deformations) are usually the result of an eye disease and are observed in:

1. Congenital ectopic pupil, when the deformation is directed mainly upward and outward, often accompanied by dislocation of the lens and other ocular anomalies
2. Iritis or partial absence of the iris, with adhesions and partial atrophy of the iris (eg, in tabes dorsalis).

Other disorders include pupillary hippus (spontaneous, partially rhythmic contractions that may occur normally but are also seen in cataracts, multiple sclerosis, meningitis, contralateral vascular strokes, or during recovery from oculomotor nerve palsy).

Bilaterally constricted pupils with normal or slightly weakened reaction to light may be found in some people - as an individual feature; among healthy individuals as a normal reaction to intense lighting, traumatic objects in front of the eyes, various threatening moments (protective reflex); in patients with severe diabetic damage to the postganglionic sympathetic fibers going to the dilator pupil; in patients with gliomas, ependymomas of the spinal cord, with a process in the area of the ciliospinal center; in patients with syringomyelia.

Bilaterally constricted pupils with a sharply weakened or absent reaction to light may occur in conditions accompanied by trophotropic shifts (during sleep, digestion, moderate arterial hypotension, vagotonia); in neurological diseases (meningeal processes, encephalitis, brain tumors, syphilis, Argyll Robertson syndrome); in psychogenic and mental diseases (hysteria, epileptic dementia, depression, imbecility); in intraorbital diseases (glaucoma, increased blood pressure in the vessels of the iris in the elderly); in poisoning with opium, morphine, bromine, aniline, alcohol, nicotine; in uremic coma.

Bilaterally dilated pupils with preserved pupillary response to light may occur in the following cases: in conditions and diseases accompanied by ergotropic shifts (thyrotoxicosis, arterial hypertension, eclampsia of pregnant women, feverish conditions, acute inflammatory process, increased attention, danger); as a characteristic feature of vegetatively labile individuals, sympathotonics; in the same pathological conditions as constricted pupils with normal response to light, only at earlier stages, stages of diseases, i.e. at the stage of irritation of the sympathetic pathways going to the pupil (diabetes mellitus, syringomyelia, gliomas, ependymomas of the spinal cord); in people using contact lenses.

Dilated pupils with absent or sharply weakened reaction to light occur in cases of poisoning with atropine, cocaine; mushrooms, plants containing anticholinergic poisons; quinine, carbon monoxide; when using mydriatics (including drugs that at least partially contain atropine); botulism; severe damage to the midbrain.

Anisocoria is the inequality of the pupils of the right and left eyes. Dilation of the pupil on one side and preservation of the reaction to light can be observed in Pourfour du Petit syndrome (pupil dilation, exophthalmos, lagophthalmos), irritation of the sympathetic pathways to the pupil by pathological processes in the neck area, local action of sympathomimetic drugs (when instilled into the eye), migraine, cluster syndrome. Irritation of the sympathetic pupillary pathways on one side leads to dilation of the pupil on the same side.

Dilation of the pupil on one side with absence or weakening of the reaction to light can be observed in Adie syndrome, unilateral damage to the oculomotor nerve, posttraumatic iridoplegia, diphtheria (damage to the ciliary nerves). The cause is paresis or paralysis of the sphincter of the pupil due to interruption of the parasympathetic pupillary pathways in the ciliary ganglion or distal.

Constriction of the pupil on one side and preservation of the reaction to light are most often found in Horner's syndrome. This syndrome occurs with damage to the lateral parts of the pons, medulla oblongata, as well as with damage to the ciliospinal center and the corresponding pre- and postganglionic sympathetic fibers (alternating syndromes of Babinski-Nageotte, Sestan-Chene, Wallenberg-Zakharchenko; syndromes of Villaret, Pancoast, Dejerine-Klumpke, Murphy, Naffziger, Romberg, Godtfredsen).

Constriction of the pupil on one side with a sharply weakened reaction to light or its absence occurs in pathology of the ciliary node (Charlin syndrome: pain in the inner angle of the orbit, rhinorrhea, herpetic keratitis, lacrimation), local action of cholinomimetics, a combination of Horner's syndrome with intraorbital pathology on the same side (glaucoma). The reason for this is irritation of the parasympathetic pupillary fibers on one side, leading to spasm of the sphincter of the pupil on the same side.

Perfect symmetry is not characteristic of the body: a small difference in pupil size is quite common. Almost a quarter of the normal population has clinically noticeable (0.4 mm or more) anisocoria. This phenomenon becomes more pronounced with age; this degree of anisocoria occurs in 1/5 of people under 17 years of age and in 1/3 of people over 60 years of age. There is anisocoria that decreases in bright light. It is not a sign of any disease and is called "simple anisocoria".

Hippus - rapidly alternating constriction and dilation of the pupil, independent of external stimulation - can occur in healthy people, but is also observed in the onset of cataracts, multiple sclerosis, meningitis, strokes, narcolepsy, and during recovery from damage to the third cranial nerve.

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