The pupils and their reflexes

The pupil, from the Latin pupilla, is nothing more than an opening located in front of the lens. It is the central part of the iris (the coloured part of the eye). The diameter of the lens is between 3 and 8 mm. It is responsible for the amount of light falling on the retina and, importantly, protects the entire interior of the eyeball from too much illumination. The diameter of the pupil varies according to the contractions of the sphincter and dilation muscles and changes in light. A healthy pupil responds smoothly to changes in illumination, with the help of the iris muscles. When the iris contracts, the pupil becomes very small, allowing little light to enter. On the other hand, when the pupil dilates, a large amount of light enters the eye.

The size of the pupil changes during the lifespan of an individual, in early childhood the pupil is very narrow, in adolescence the pupil widens, and in middle age the pupil narrows again.

Changes in pupil size and shape and their causes

A person's pupils should be the same size. Small disproportions are not a cause for panic (an almost imperceptible difference in the size of the right and left pupil may be a physiological or congenital feature). Pathological pupillary constriction can be of two types.

These include:

spastic constriction (caused by contraction of the pupil sphincter),
paralytic constriction (resulting from paralysis of the pupil dilator).

Changes in pupil size and shape also occur during:

Strong fear, terror - the pupil becomes large and takes on a round shape.
When experiencing various strong emotions e.g. love, emotion (pupil enlargement).
Damage to the oculomotor nerve (strong pupil dilation).
Diseases of the stomach (small pupils).
Disorders of the blood supply to the brain (distortion and oval shape of the pupils).
Neurosis (enlarged pupils).
Insomnia (large, round or oval pupils).
Use of various types of medication (e.g. atropine, homatropine, hyoscine and eumydrin) where severe pupillary dilatation occurs.
Drug use (e.g. cocaine)-increased pupil size.
Eye or head injuries.
Tumours of the brain, which at first gently over time presses more and more heavily on the neural structures leading to disturbances in the normal function of the eye. This can also result from increased intracranial pressure. This condition poses a direct threat to the patient's health and life
Various types of illnesses, including lung disease, with multiple sclerosis.
Pre-migraine aura (anisocoriasis often occurs).
Ocular infections.
Damage to the oculomotor nerve, i.e. the 3rd cranial nerve (here we are most often dealing with unilateral pupillary dilatation).
Stroke (especially with primary vascular damage to the brainstem).
Trauma or following neurosurgery.
Presence of aneurysms in the brain (severe pupillary dilation).
Pupillitis (dilated pupils).
Acute glaucoma and chronic inflammatory glaucoma (the pupil takes on an oval shape, is dilated and a greenish glare is visible in the pupil).
Pott's disease (constriction of both pupils or only one).
Spinal cord tumours (constriction of only one pupil).
Thyroid excision (pupil dilation albeit short-lived).

The pupillary reflexes are very often examined by various types of doctors (usually neurologists, ophthalmologists or neurosurgeons) after any trauma (blows, haemorrhages, accidents) in which the patient has lost consciousness. it is worth remembering that after trauma, one of the pupils may be dilated or constricted and the other normal.

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Change in pupil size and shape - causes

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