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eye health

anisocoria

Generality

Anisocoria is the different amplitude of the two pupils, which can also be observed when they are placed at the same degree of illumination. It may be a physiological anomaly, which you need not worry about, or the sign of a morbid condition that requires immediate medical intervention.

Figure: note the different diameter between the right pupil and the left pupil. From the site: wikipedia.org

Some of the most dangerous causes of anisocoria are: brain cancer, brain aneurysm, meningitis and severe head injuries.

The symptoms that accompany the anisocoria are very varied and depend on the underlying pathological state (ie on the reasons that caused the anisocoria itself).

In order to cure the anisocoria, it is necessary to diagnose the exact causes of the problem; otherwise, or if prompt action is not taken, the patient runs serious risks.

What is anisocoria?

The anisocoria is the different amplitude of the ocular pupils, observable also in identical lighting conditions of the two eyes.

In other words, there is anisocoria when the pupils, despite being exposed to the same amount of light, have different diameters from one another.

WHAT IS PUPIL?

The pupil of the eyes is a hole located in the center of the iris, which allows light to strike the lens first and then the retina. The crystalline, in fact, is a lens that focuses the incoming light; the retina, on the other hand, is the membrane located on the inner surface of the eye, which, thanks to the presence of photoreceptors (cones and rods), is sensitive to light and able to communicate with the brain via the optic nerve .

The diameter of the pupil varies according to the light present in the environment and which affects the eye; these changes are regulated by a very precise system of muscles, which is dependent on the third pair of cranial nerves (or oculomotor nerves ).

The pupil narrowing occurs by a muscle that surrounds the iris, called the constrictor muscle (or sphincter) of the iris ; in full light, this muscle narrows the pupil up to 1.5 millimeters.

The dilation, instead, takes place thanks to the muscles that are placed perpendicularly to the constrictor muscle of the iris; these, in the dark, make the pupil widen up to about 8 millimeters in diameter.

WHAT DIFFERENCE DOES THEY HAVE TO DO BETWEEN THE TWO PUPILS TO TALK ABOUT ANISOCHORY?

In order to talk about anisocoria, there must be a difference of at least 0.4 mm between the two pupils.

A lower deviation is not considered an anomaly worthy of note and cannot be classified as anisocoria.

Causes

Anisocoria can arise from different causes, being linked to particular morbid states but also to the intake of certain pharmacological substances or to unusual health conditions. Furthermore, it is good to remember that a part of people with anisocoria has no predisposing diseases or uses drugs or toxic agents due to the disorder; in all these conditions we speak of physiological anisocoria.

Below is a list of the main causes of anisocoria.

  • Physiological anisocoria . It has been calculated that about 20% of healthy people (ie without any nerve-ocular pathology and who do not take drugs or predisposing substances) have a singular difference (greater than 0.4 millimeters but less than a millimeter) between the two ocular pupils.
  • Horner syndrome . It is a disease caused by a defect of nerve transmission between the brain and the oculo-facial muscles of only one side of the face; it is mainly characterized by three signs: persistent miosis, ptosis of the eyelid and anhidrosis.

    Persistent miosis is the condition in which the pupil remains narrow in diameter even in the absence of light; the ptosis of the eyelid is the complete or partial lowering of the upper or lower eyelid (in fact, it is also called the lowered eyelid); finally, anhidrosis is the inability to produce (or secrete) sweat which, in the case of Horner's syndrome , can affect all half of the face involved or only a small part.

  • Events of a traumatic nature that affect the eye . One-eye contusion, cataract surgery, or eye inflammation (such as uveitis, closed-angle glaucoma, etc.) can cause adhesion between the back of the iris and the anterior part of the lens; this may affect the pupil narrowing and dilation mechanisms (obviously, at the level of the eye involved). The anisocoria that has traumatic origin is also called mechanical anisocoria.
  • Adie tonic pupil (or Adie's syndrome) . It is a neurological disease characterized by a pupil that responds more slowly (than normal) to light stimuli. In other words, dilation and pupillary constriction occur longer than normal. The tonic pupil of Adie mainly affects women.
  • Paralysis of the oculomotor nerve . The paralysis of the oculomotor nerve can be caused by a cerebral aneurysm, a blow to the head, an ischemia of the oculomotor nerve or a brain tumor. These conditions generally act by compressing the oculomotor nerve and impairing its normal functions.
  • Pharmacological agents . May cause anisocoria: the drops based on pilocarpine or tropicamide, a cough medicine called dextromethorphan, the alkaloids (for example the scopolamine) contained in some plant species (genera Brugmansia and Datura ) and, finally, some drugs such as cocaine and MDMA (Ecstasy).
  • Meningitis . It is the inflammation of the membranes (meninges) and / or of the cerebrospinal fluid (liquor) that surround the brain and the spinal cord. It can be triggered by infectious agents (viruses and bacteria) or non-infectious agents (sarcoidosis, systemic lupus erythematosus, etc.).
  • Migraine . It is a pathological condition characterized by unilateral headaches (ie on only one side of the head), which tend to worsen and are capable of causing intense and throbbing pain.
  • Epilepsy . It is a neurological disease characterized by a hyperactivity of some brain nerve cells.

Anisocoria, therefore, can be the sign of a serious pathology, which, if not treated immediately, can also lead to death.

Some life-threatening causes of anisocoria:

  • Horner syndrome, especially when it is caused by a carotid or jugular problem.
  • Brain aneurysm
  • Strong blow to the head
  • Brain tumor
  • Use of cocaine and MDMA

Symptoms

Physiological anisocoria does not cause any particular symptoms or signs.

On the contrary, the anisocoria related to certain morbid states or particular health conditions may be accompanied by:

  • Blurred and / or double vision . It can be the result of a brain tumor, a brain aneurysm, a severe head trauma, an oculomotor nerve damage ischemia or uveitis.
  • Fever It can occur in case of meningitis.
  • Headache . It can be linked to various conditions: a meningitis, a migraine, a brain tumor, a brain aneurysm or a severe head injury.
  • Confusion . It may be related to a brain tumor, a brain aneurysm or a strong blow to the head.
  • Loss of sight . It can be induced by a brain tumor, a brain aneurysm or an oculomotor nerve ischemia.
  • Sensitivity to light . It may be related to Adie's syndrome, a brain aneurysm, or an oculomotor-damaged ischemia.
  • Nausea . It can come from a brain aneurysm, from a migraine, from a severe blow to the head or from a brain tumor.
  • Stiff neck . It can be the consequence of a brain aneurysm or migraine.
  • Epileptic crises . In addition to epilepsy, they may be due to a brain tumor, a brain aneurysm or an oculomotor nerve ischemia.
  • Waning eyelid . It can mean not only Horner syndrome, but also cerebral aneurysm.
  • Marked mydriasis . It may mean that an oculomotor nerve paralysis is underway (for example due to head trauma) or that cocaine has been used.

WHEN TO REFER TO THE DOCTOR?

Figure: person with Horner syndrome. From the site: wikipedia.org

If the anisocoria appears suddenly or after a blow to the head, or if it is associated with severe pain in the head, it is better to contact your doctor immediately and have him examined.

In the case of physiological anisocoria, a medical consultation is advised if the difference between the pupils worsens markedly or one of the previously mentioned symptoms is felt.

Diagnosis

Note a difference in diameter between the two pupils is quite simple, both for the doctor and for the same patient with anisocoria (as it is sufficient that you look in the mirror).

The most important thing to do, when presenting an anisocoria case, is to quickly establish what the causes may be; in fact, pupils of different diameters could be the consequence of a very serious and life-threatening pathology.

Therefore, the patient is obliged to communicate to the doctor any warning symptom and any unusual event that may have happened to him before the onset of anisocoria (for example a blow to the head, an injury to an eye, etc.).

Without an exact diagnosis of the triggering causes, it is impossible to plan a proper treatment; consequently, without appropriate and / or timely care, unpleasant consequences may occur.

DIAGNOSTIC EXAMINATIONS

In addition to the objective examination, through which the doctor evaluates the extent of anisocoria and with what symptoms it presents, the patient could be subjected to:

  • Complete blood count .
  • C-reactive protein test, erythrocyte sedimentation rate (ESR) and leukocyte formula . There are three special blood tests that measure the level of inflammatory markers in the bloodstream. They are useful in case of meningitis and in case of eye inflammation.
  • Lumbar puncture and cerebrospinal fluid analysis . It is particularly indicated in suspected cases of meningitis, as it allows to establish which are the triggers of inflammation at the level of the meninges.
  • Eye drops test . It consists in instilling, in the patient's eye, eye drops containing different pharmacological substances to study their effects at the pupil level. It is very useful in case of suspected Horner syndrome.
  • CT scan (or computerized axial tomography), nuclear magnetic resonance (or MRI) and head X-rays . There are three diagnostic imaging tests that can be used to identify a brain tumor, Adie's syndrome, a brain aneurysm, head trauma, damage to the oculomotor nerve, etc.

ANISOCORIA IN CONDITIONS OF LIGHT FIOCA AND IN CONDITIONS OF INTENSE LIGHT

For diagnostic purposes, it is useful to know that:

  • The anisocoria that appears or becomes accentuated in poorly lit environments could be linked to Horner's syndrome or to ocular trauma (mechanical anisocoria).
  • The anisocoria that occurs above all in the presence of intense light, on the other hand, could be a sign of Adie's syndrome, of a paralysis of the oculomotor nerve or of a recent intake of certain pharmacological / toxic substances.

Treatment

The therapy to be adopted in the presence of anisocoria varies according to the triggering causes. For example:

  • If infectious meningitis is in progress, antibiotics or antiviral drugs should be administered, depending on whether the cause is a bacterium or a virus, respectively.
  • If a tumor has formed inside the brain, surgery is required to remove it.
  • If the patient has suffered a severe blow to the head, it may be necessary to drain any hematoma formed inside the skull.

IN CASE OF PHYSIOLOGICAL ANISOCORY

For people with physiological anisocoria is not expected and no treatment is needed.

Prevention

Preventing anisocoria is somewhat complicated, because some conditions that cause its appearance are also difficult to prevent (for example, brain cancer is a neoplasm that arises suddenly and without precise reasons).

If you are practicing work or sports in which it is possible to suffer trauma to the eye (so you are at risk of mechanical anisocoria), it is advisable to wear the most appropriate protections (helmets, etc.).

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