Why does the pupil size decrease with age?

useful information

What is the job of the pupil?

The opening in the middle of the eye, surrounded by the iris (rainbow skin), is called the pupil. It has an important function in the visual process. By regulating their size, the amount of light falling into the eye can be controlled and the image quality can be improved. Changes in the pupillary response can be caused by neurological disorders or by eye diseases themselves.

Natural pupil size

The width of the pupil normally ranges from approx. 1mm to 8mm. In daylight or in bright rooms, the pupil becomes constricted (miosis) while it expands in the dark (mydriasis). When looking at objects close by, the pupils are also constricted; this increases the depth of field. The pupil diameter is usually the same in both eyes (isokor), but minor deviations are not necessarily pathological. While adolescents tend to have dilated pupils, pupils constrict with age. Other natural deviations occur with:

  • Joy, fear, stress, fright: dilated pupils
  • Fatigue while sleeping: narrow pupils

Disorders of the pupil size

Pupillary motor disorders can be caused by a variety of triggers. In addition to diseases of the eyes, from the neurological and internal medicine group, the intake of certain medications, drugs and poisoning can also lead to changes in the pupil size.

Horner syndrome

Local damage to the sympathetic, autonomic nervous system can result in what is known as Horner's syndrome. In addition to a pupillary constriction on the affected side, there is a hanging upper eyelid (ptosis), a smaller-looking eye (pseudoenophthalmos) caused by a higher position of the lower eyelid and, in some cases, a reduced secretion of sweat. The Horners syndrome can be triggered by different diseases:

  • Tumors
  • Injuries
  • Dilated blood vessels
  • Inflammation
  • Blood circulation disorders

The ophthalmologist can make the diagnosis by checking the light reaction and applying special eye drops. Treatment depends on the cause.

Rigid, unresponsive pupils

If the pupils fail to respond to light, this is known as pupillary rigidity. A medical examination should always be carried out. Depending on the cause and location of the damage, a distinction can be made between:

Absolute pupillary rigidity

The pupil motor skills of the diseased eye are suspended here. Causes can be bleeding, inflammation, tumors or vasodilatation in the area of ​​the eye socket or the base of the skull. This results in damage to the nerve fibers that are responsible for the muscles of the eyes and thus for the pupillary motor skills.

Reflective pupillary rigidity

When the eye is illuminated, the pupils naturally react by constricting both the illuminated and the partner's eye (indirect reaction to light stimulus). In the case of reflex pupillary rigidity, the width of both pupils remains unchanged despite the light stimulus. Convergence, however, is intact; if an object is fixed, the pupils are constricted on both sides. In addition to tumors and bleeding, the cause of this disorder can be an infectious disease (tick bite, sexually transmitted diseases) or it can be caused by alcoholism.

Amaurotic rigidity of the pupil

Amaurosis means blindness or the complete lack of light perception. If the sick eye is illuminated, neither this nor the partner eye reacts with a narrowing. The cause lies in a one-sided malfunction of the sensors. It can occur due to retinal detachment, inflammation of the optic nerve, damage to the optic nerve, or occlusion of blood vessels in the eye.

Amaurotic pupillary rigidity is a disorder of the pupillary reaction caused by blindness. The diseased eye does not react to direct light stimuli, but the indirect pupil reaction is retained (i.e. if the healthy eye is illuminated, the pupil of the diseased one also becomes smaller).

Poisoning, drugs and medication

Ingested toxins, medication and drugs also reach the eye via the blood vessels and can lead to changes in the pupil size. In these cases, both eyes are equally affected.

Dilated pupils (mydriasis) can occur in connection with the consumption of the following substances:

  • Poisoning with carbon monoxide (CO) or atropine (deadly nightshade)
  • Overdose of antidepressants and Parkinson's medication
  • cocaine

Constricted pupils (miosis) occur with mushroom poisoning and after taking opiates (morphine, heroin).

Changes in the pupil can occur as a result of body reactions in certain situations or age-related in the course of life and are then harmless. However, a change in the pupil size or a lack of reaction to light can also be an expression of a serious illness or poisoning and should therefore always be assessed by a doctor. Contact your ophthalmologist in Zurich Wallisellen, we will be happy to help you.

This article corresponds to the current state of science

Ophthalmologists Zurich2017-06-25Ophthalmologists Zurich - Wallisellen Center