The pupil is the black central part of the eye. The pupils enlarge (dilate) in dim light and get smaller (contract) in bright light.
Discordia is when human pupils differ in size. Discordia is the medical term used to refer to any abnormality in the shape of the pupil of the eye.
Some people have pupils that are slightly different in size or shape, so the variations can be expected and are generally harmless.
It is generally considered benign, although it must be distinguished from congenital Horner syndrome, drug dilation, or other conditions related to the sympathetic nervous system.
The prevalence of Discordia is not influenced by the subject’s sex, age, or iris color.
However, if there is a significant difference or one of the pupils has recently changed, there could be an underlying problem.
The pupil is the hole in the center of the iris (the colored part of the eye), and its primary function is to control the amount of light that enters the eye. The pupils do this by contracting and dilating, making them appear smaller and more significant.
It is called anisocoria, with several different causes when your pupils are of different sizes.
Sometimes your pupils will return to standard size without needing treatment, but you should seek medical attention if the condition persists or trauma or head injury has followed.
Is it serious?
Discordia is not a disease in itself and may not affect the patient’s health, but it can also be a sign caused by various conditions, from eye nerve damage caused by strokes to tumors or trauma.
Therefore, if a difference in pupil size is detected, it is imperative to urgently go to the ophthalmologist to rule out any risky situation.
In that case, an appointment should be made with the Department of Neuro-ophthalmology, where all the necessary tests will be performed.
Around AD 200, Galen compared the iris to an elastic circular ring passively inflated or deflated by vital spirits sent from the brain to improve vision.
It was not until the first half of the 18th century that it was widely accepted that the iris movement and pupil size were due to the active interaction of two muscles of the iris: a longitudinal radial dilator and a circular sphincter muscle.
Many contributions were made to our understanding of the physiology and pathology of the pupils in the 20th century, including the description of the oscillating lantern test to assess a relative afferent pupillary defect by Thompson in 2003.
If the size of the pupils is very uneven, a person may notice the discrepancy. More often, uneven pupils are noticed only during a medical exam.
The unequal pupils usually cause no symptoms, but a person may occasionally have trouble focusing on nearby objects.
The main distinguishing feature of Discordia is a difference in the shape and size of the pupil or both pupils, such that the pupils differ between the two eyes.
In any given eye exam, up to 41% of healthy patients may show an anisocoria of 0.4 mm or more at one time or another. It can also happen since the difference between the two pupils varies daily.
An average population survey showed that differences of 1 mm were found on average between the pupils in low light or near dark conditions.
The presence of Discordia has been estimated in 20% of the average population, so a certain degree of pupil difference can be expected in at least 1 in 5 clinical patients.
These more noticeable symptoms are often the reason people seek medical attention. If you have no other symptoms, you can compare the size of your pupils with old photos of yourself to figure out when it happened.
This is rare, but it can be a sign of a bigger problem if the anisocoria occurs or if the size of your two pupils is suddenly different for no reason.
Causes of Discordia
The pupil is an opening in the center of the iris through which light enters the eye. The size of the pupil can vary in response to the intensity of light and neurological stimuli.
Any disorder that physically damages the mechanical compliance of the iris or the iris musculature can result in an irregular pupil. Blunt trauma to the eye can cause focal tears in the sphincter muscle.
An iridodialysis occurs when the outer edge of the iris separates from its ciliary connection. Intraocular inflammation can damage the iris or cause it to adhere to the lens or cornea (synechiae).
Neovascularization can also distort the iris and alter pupillary reactivity. Iris malformation, such as coloboma and aniridia, will affect the size and function of the pupil.
The leading cause of a deformed pupil in an adult is probably cataract surgery, but any surgical procedure in the anterior segment can have similar results.
To avoid unnecessary extensive neurological evaluation, it is essential to recognize that these structural abnormalities of the iris cause abnormal pupil size, shape, and reactivity.
It should be considered a genetic or developmental phenomenon when detected during childhood, without any other symptoms and when other disorders are ruled out through clinical testing.
Asymmetric pupil or slag, a potential cause of anisocoria, refers to an abnormal pupil shape due to developmental and intrauterine abnormalities.
There are many causes of pupillary abnormalities. Any process that affects the autonomic innervation of the iris muscles or damages the iris muscles themselves will cause an abnormality in the pupil.
For example, a dorsolateral brain stem stroke can damage the central neuron of the oculosympathetic pathway to cause ipsilateral meiosis and poor pupillary dilation (Horner syndrome).
Miosis can also result from local trauma to the iris that causes mechanical restriction of pupillary movement.
Systemic autonomic neuropathies, such as diabetes mellitus, can denervate the iris sphincter muscle and cause a poor pupillary lumen reaction. A tonic pupil can also result from local inflammation of the ciliary ganglion.
The larger or smaller pupil may be abnormal depending on the cause.
Types of Discordia
Pupillary Discordia can involve the afferent or efferent pathways. Anisocoria, which is not physiological, indicates a problem with the efferent pupillary pathway, either parasympathetic or sympathetic.
Disorders of the parasympathetic system affect the light response, including third nerve palsy and a tonic pupil. Iris disorders, including the application of cholinergic agents, should also be considered in the impaired pupillary light reaction.
There are several main types of abnormalities in the pupil (Discordia):
Varying pupil size (anisocoria), irregular pupil shape, pupil displacement (corectopia), asymmetric pupillary reaction (relative afferent pupillary defect), and episodic abnormalities.
large unilateral pupil
This is a pupil that shows poor constriction in a well-lit room. Causes include:
- Traumatic damage to the iris.
- Third nerve palsy.
- Rubeosis iridis (neovascular eye disease).
- Holmes-Adie syndrome: can also be irregular and unusually one-sided.
- Drug dilation (i.e., dilation drops).
Small unilateral pupil
This is a pupil that shows poor dilation in low light conditions. Causes include:
- Physiologically small pupil.
- Uveitis with synechiae. Horner’s syndrome.
- Argyll Robertson pupil (can also be irregular, usually bilateral).
- Drug constriction (constriction of drops).
Poorly reactive to light with a good near response (near light dissociation), abnormal shape or position (corectopia), and change in size and reactivity.
The abnormality can be transient or constant. Pupillary abnormalities are often asymptomatic or observed by an observer.
Occasionally, patients complain of photophobia in an eye with a large pupil (mydriatic) because the increased light reaches the retina through the widest opening.
Because the parasympathetic system innervates the pupilloconstrictor and ciliary muscle to accommodate, patients with oculomotor nerve palsy or short ciliary nerve damage may report blurred near vision (such as while reading) in addition to the larger pupil size.
Abnormal pupil shape
The human pupil must be round. Many other pupillary shapes, including vertical and horizontal slits, rectangles, and crescents, are seen in nature.
A fixed oval pupil, associated with severe pain, red eye, cloudy cornea, and systemic discomfort, suggests acute angle-closure glaucoma.
Conditions that could be affecting the size or shape of the pupils
These are some reasons the pupils can be of different sizes or shapes.
Dilated pupils can be a symptom of certain migraines. This specific type of severe headache is believed to cause abnormal paralysis of the motor nerves in the eye.
This not only causes persistent dilated pupils, but the headache is focused around the eyes. Those who also suffer often complain of blurred vision.
Holmes-Adie syndrome (JHS) is a neurological disorder in which one pupil is significantly larger than the other and contracts slowly under bright lights.
It is believed to be caused by a viral infection that causes inflammation and damage to the part of the brain that controls eye movement.
The condition generally progresses slowly in one eye before developing in the other. People with Holmes-Adie syndrome can also experience profuse sweating, which is more common in young women.
Horner syndrome is another neurological disease that can arise for several reasons, including tumors and medical treatments. The condition affects the sympathetic nervous system, responsible for the body’s fight or flight mechanism.
Horner is characterized by abnormally small pupils and can be accompanied by a droopy eyelid and bloodshot eyes. Decreased sweating on the affected side of the body is also common.
A coloboma is a gap in one of the eye’s structures, and when it affects the iris, it can make the pupil misshapen. Colobomas are most common in the lower half of the iris, giving the pupil a characteristic keyhole shape.
Colobomas are congenital, which means they are present from birth and are due to the baby’s eyes not developing correctly during pregnancy.
The impact on your vision will depend on where the coloboma is located, although those in the iris generally have a limited effect on vision.
When the iris becomes inflamed, it is called iritis. The condition is classified as traumatic due to an injury to the eye, or non-traumatic, usually due to infection or disease.
The most common symptoms include bloodshot eyes, eye pain, headaches, blurred vision, and small or misshapen pupils. You are also likely to experience pain when a bright light is shone on the affected eye.
Other underlying causes
It is difficult to diagnose why you may have differently sized or irregularly shaped pupils without visiting an optometrist. However, there are several more serious reasons for suffering from anisocoria. These include:
- Brain abscess.
- The tumor is cerebral.
- Bleeding in the brain.
These are rare conditions, but it is essential to seek medical help if you have anisocoria and want to rule it out.
Drugs that affect the pupils
Many drugs can affect pupil size, both topically applied and generally ingested.
Such drugs can be drops to treat eye disorders (for example, homatropine used for certain inflammatory disorders or lesions or Pilocarpine used for glaucoma).
Pointed pupils caused by opiate use are a barrier to evaluating the brain-injured patient.
Topical mydriatics are widely used in ophthalmic practice to allow a complete eye examination.
Dilation: sympathomimetics (such as phenylephrine, Adrenaline (epinephrine)) and antimuscarinics (such as cyclopentolate, tropicamide, and Atropine).
Constriction: muscarinic agonists (such as Pilocarpine).
Dilation: sympathomimetics (such as Adrenaline (epinephrine)) and antimuscarinics (such as Atropine), tricyclic antidepressants, amphetamines, and ecstasy.
Constriction: opiates (such as morphine and organophosphates).
The goal is to decide whether the larger or smaller pupil represents the problem. This refers to uneven pupils. Discordia is physiological (and harmless) in about 20% of people.
New-onset Discoria may suggest a severe underlying condition, such as Horner syndrome due to carotid dissection or third nerve palsy due to an aneurysm.
It is necessary first to determine which pupil is behaving abnormally. Compare the pupils in dim and light conditions:
If a poor reaction (slow, partial, or absent) to light in one eye and the anisocoria is more evident in a well-lit room, the affected pupil is abnormally large.
If there is an excellent reaction to light in both eyes but poor, slow, or absent dilation in the dark (i.e., the Discordia is enlarged), the affected pupil is abnormally small.
The variation between the eyes should not be more than 1 mm: both eyes should react to light normally. Usually, the pupils react (that is, the contract) similarly.
Comparing the direct and consensual reaction to light in both eyes helps localize a lesion, remembering that the retina and optic nerve are necessary for the afferent signal and that the oculomotor nerve provides the efferent component of the direct and consensual reflexes.
If the optic nerve of the first eye is damaged: the reflection of direct light is lost in the first eye, as is the consensual effect in the second eye, since it does not receive any message.
However, the oculomotor nerve in the first eye is intact, so your pupil will still contract when light shines into the other eye.
If the optic nerve of the second eye is damaged, when the light is shone on the first (normal) eye, the second eye will still show a consensual constriction, as its oculomotor nerve is intact.
If the oculomotor nerve in the first eye is damaged, it cannot produce a direct light reflection as the motor component is lost. However, the optic nerve still transmits the afferent signal so that the other eye will contract consensually to the light.
If the oculomotor nerve of the second eye is damaged, when the light is shone in the routine first eye, there is no consensual constriction of the second.
When to see a doctor
People with warning signs should see a doctor immediately. People without warning signs but who have other symptoms should call a doctor.
The doctor can decide how quickly they should be seen based on your symptoms.
What the doctor does
Doctors first ask questions about the person’s symptoms and medical history, including questions about smoking.
Doctors then do a physical exam. What they find during the history and physical examination often suggests a cause for the uneven pupils and the tests that need to be done.
Doctors ask if the person has recently had a head or eye injury, what eye drops the person has used, and if they have ever had an eye disorder or eye surgery.
Doctors examine the entire eye, usually using a slit lamp (an instrument that allows the doctor to examine the eye under high magnification). Other ocular symptoms are evaluated as necessary.
Doctors may use eye drops to test how the pupils respond to medications that cause the pupils to contract or widen.
Tests for Discordia
Testing is usually unnecessary unless people have other symptoms.
Pupil testing can reveal severe neuro-ophthalmic and retinal disease and should be incorporated into every comprehensive eye exam.
With careful clinical examination, this test can aid in diagnosing and managing many of these conditions at the primary care level.
The pupil examination is to the eye what deep tendon reflexes are to the neurological examination: objective, helpful, and challenging to falsify. The “without fail” examination of the pupil includes:
Measurement of pupil size in light and dark, evaluation of the light reaction of the pupil in each eye, and the oscillating flashlight test to determine the presence of a relative afferent pupillary defect. If one or both pupils do not react well to light, more tests are done.
People with Horner syndrome or third cranial nerve palsy usually require magnetic resonance imaging (MRI) or computed tomography (CT). People who have Horner syndrome may also need a chest CT scan.
The treatment of uneven pupils is in itself unnecessary. However, the underlying disorder may need to be treated.
As it is not a disease in itself, Discordia may, in several cases, not need treatment.