How can the pupillary reflex be tested? | The pupil reflex

How can the pupillary reflex be tested?

The examination of the pupillary reflex is one of the standard examinations in neurology. The pupillary reflex can be tested by means of a flashlight examination. This involves illuminating one eye and examining the reaction of both eyes.

If deviations occur, this is called anisocoria. Normally, the doctor examines each eye individually, i.e. the illuminated eye is tested for the direct pupil reaction and the unilluminated eye for the consensual reaction. Often one hand is held between the eyes so that the other eye does not receive light from the flashlight.

  • The incidence of the flashlight causes the pupils to contract, this is called a direct pupillary reaction.Under healthy conditions, however, not only the illuminated eye, but also the eye on the opposite side reacts with a narrowing of the pupils. This is called a consensual or indirect pupil reaction. Both eyes should have the same width, this is called isocorrection.

What causes disorders of the pupillary reflex?

In disorders of the pupillary reflex, a distinction is made between damage that affects the afferent thigh, i.e. the nerves that transmit information from the retina to the brain, and damage that affects the efferent thigh, i.e. the nerves that carry information from the brain to the eye muscles.

  • Damage to the afferent thigh usually affects parts of the optic nerve.

    During the examination, a disturbed direct pupil reaction can be detected, i.e. when the affected eye is illuminated, there is no pupil constriction, whereas when the healthy eye is illuminated, there is a constriction in both. Causes can be injuries, inflammations or tumors in the area of the optic nerve, but also cerebral hemorrhages and multiple sclerosis.

  • Damage to the efferent leg affects the motor nerve, which is responsible for the innervation of the muscles responsible for the pupillary response (oculomotor nerve). A disorder in this area is manifested by a lack of direct or consensual pupil response in the affected eye.

    This can be caused by inflammation, injuries or tumors in the area of the oculomotor nerve, but also by a lack of oxygen.

Drugs and other drugs exert their effect by inhibiting or activating sympathetic or parasympathetic nerves in the CNS. The pupil reaction is also innervated via such fibers. While the sympathetic nerve causes a dilation (mydriasis) of the pupil, activation of the parasympathetic nerve causes a constriction (miosis) of the pupil.

Further interesting information on this topic can be found at Which medications or drugs influence the pupil?

  • Drugs like opiates and nicotine activate the parasympathetic nervous system. This triggers relaxation, anxiety release and pain relief in the body.

    In addition, they also lead to a narrowing of the pupil. In the case of an overdose of opiates, patients often have a pupil that is as small as possible, which is why it is called a pin-sized pupil.

  • Other drugs, such as amphetamines, speed, ecstasy, cocaine, etc. activate the sympathetic nervous system.

    The intoxicating effect is noticeable in increased euphoria, increased concentration, increased self-confidence, increased libido, etc. Side effects include a dilation of the pupils, which is often very quickly noticeable during police checks.

Multiple sclerosis is a chronic inflammatory disease of the central nervous system, in which the myelin sheaths in the nerves are destroyed. The symptoms are very diverse and the causes are still not completely understood.

However, it is assumed that demyelination of the nerve fibers in MS leads to damage in the area of the afferent thigh, i.e. the optic nerve. Often, damage to the pupillary reflex is not the only symptom of MS patients, and they usually also suffer from double vision due to eye muscle paresis and other visual disorders.

  • This damage is noticeable by the absence of direct pupillary response in the affected eye.
  • However, the consensual pupillary response in the illuminated contralateral eye remains the same.