Anisocoria is a common condition, defined by a difference of 0.4 mm or more between the sizes of the pupils of the eyes.

Anisocoria has various causes:

- Physiological anisocoria: About 20% of normal people have a slight difference in pupil size which is known as physiological anisocoria. In this condition, the difference between pupils is usually less than 1 mm.

- Horner's syndrome

- Mechanical anisocoria: Occasionally previous trauma, eye surgery, or inflammation (uveitis, angle closure glaucoma) can lead to adhesions between the iris and the lens.

- Adie tonic pupil: Tonic pupil is usually an isolated benign entity, presenting in young women. It may be associated with loss of deep tendon reflex (Adie's syndrome). Tonic pupil is characterized by delayed dilation of iris especially after near stimulus, segmental iris constriction, and sensitivity of pupil to a weak solution of pilocarpine.

- Oculomotor nerve palsy: Ischemia, intracranial aneurysm, demyelinating diseases (e.g., multiple sclerosis), head trauma, and brain tumors are the most common causes of oculomotor nerve palsy in adults. In ischemic lesions of the oculomotor nerve, pupillary function is usually spared whereas in compressive lesions the pupil is involved.

- Pharmacological agents with anticholinergic or sympathomimetic properties will cause anisocoria, particularly if instilled in one eye. Some examples of pharmacological agents which may affect the pupils include pilocarpine, cocaine, tropicamide, MDMA, dextromethorphan, and ergolines. Alkaloids present in plants of the genera "Brugmansia" and "Datura", such as scopolamine, may also induce anisocoria.

- Migraines

The eye is made up of the sclera, the iris, and the pupil, a black hole located at the center of the eye with the main function of allowing light to pass to the retina. Due to certain muscle spasms in the eye, the pupil can resemble a tadpole, which consists of a circular body, no arms or legs, and a tail.

When the pupil takes on the shape of a tadpole, the condition is called tadpole pupil. Tadpole pupil, also known as episodic segmental iris mydriasis, is an ocular condition where the muscles of the iris begin to spasm causing the elongation, or lengthening, of parts of the iris. These spasms can affect any segment, or portion, of the iris and involve the iris dilator muscle. Contractions of the iris dilator muscle, a smooth muscle of the eye running radially in the iris, can cause irregular distortion of the pupil, thus making the pupil look tadpole shaped and giving this condition its name. Episodic segmental iris mydriasis was first described and termed “tadpole pupil” in 1912 by HS Thompson

The primary symptom is pupillary distortion (changing of the size or shape of the pupil). Distortion can occur in any segment of the iris. One part of the iris is pulled to a peak, and then returns to normal after the episode. Other symptoms may include blurred vision, abnormal periocular sensations (unusual feelings around the eyes), migraines, and feelings of a chilled face. Some patients who demonstrate tadpole pupil symptoms also experienced Horner’s syndrome or Adie’s tonic pupil

Tadpole pupil symptoms occur in episodes. Episodes are generally brief and less than 5 minutes, however, some episodes have been reported to last anywhere from 3 to 15 minutes. The episodes can occur multiple times a day for days, weeks, or months.

Studies show that a majority of those experiencing tadpole pupil are younger women from an age range of 24 to 48 years old, with no apparent health problems. Although women generally have the tadpole pupil, men are not unaffected by this disease and some have been reported to experience the symptoms.

Many people of East Asian descent are prone to developing angle closure glaucoma due to shallower anterior chamber depths, with the majority of cases of glaucoma in this population consisting of some form of angle closure. Higher rates of glaucoma have also been reported for Inuit populations, compared to white populations, in Canada and Greenland.

No clear evidence indicates vitamin deficiencies cause glaucoma in humans. It follows, then, that oral vitamin supplementation is not a recommended treatment for glaucoma. Caffeine increases intraocular pressure in those with glaucoma, but does not appear to affect normal individuals.

Anisocoria is a condition characterized by an unequal size of the eyes' pupils. Affecting 20% of the population, it can be an entirely harmless condition or a symptom of more serious medical problems.

As the name implies, it is the bulge of weak sclera lined by ciliary body, which occurs about 2–3 mm away from the limbus. Its common causes are thinning of sclera following perforating injury, scleritis & absolute glaucoma.

it is part of anterior staphyloma

Hemeralopia is known to occur in several ocular conditions. Cone dystrophy and achromatopsia, affecting the cones in the retina, and the anti-epileptic drug Trimethadione are typical causes. Adie's pupil which fails to constrict in response to light; Aniridia, which is absence of the iris; Albinism where the iris is defectively pigmented may also cause this. Central Cataracts, due to the lens clouding, disperses the light before it can reach the retina, is a common cause of hemeralopia and photoaversion in elderly. C.A.R (Cancer Associated Retinopathy) seen when certain cancers incite the production of deleterious antibodies against retinal components, may cause hemeralopia.

Another known cause is a rare genetic condition called Cohen Syndrome (aka Pepper Syndrome). Cohen syndrome is mostly characterized by obesity, mental retardation, and craniofacial dysmorphism due to genetic mutation at locus 8q22-23. Rarely it may have ocular complications such as hemeralopia, pigmentary chorioretinitis, optic atrophy or retinal/iris coloboma, having a serious effect on the person's vision.

Yet another cause of hemeralopia is uni- or bilateral postchiasmatic brain injury. This may also cause concomitant night blindness.

According to recent research not a single theory is able to explain the cause fully. However current plausible theories include infection with "Toxoplasma gondii", Herpes simplex virus, Rubella, neurogenic causes, and autoimmune pathology.

It is the name given to the localised bulge in limbal area, lined by the root of the iris. It results due to ectasia of weak scar tissue formed at the limbus, following healing of a perforating injury or a peripheral corneal ulcer. There may be associated secondary angle closure glaucoma, may cause progression of the bulge if not treated. Defective vision occurs due to marked corneal astigmatism. Treatment consists of localised staphylectomy under heavy doses of oral steroids.

Pigment dispersion syndrome (PDS) is an affliction of the eye that can lead to a form of glaucoma known as pigmentary glaucoma. It takes place when pigment cells slough off from the back of the iris and float around in the aqueous humor. Over time, these pigment cells can accumulate in the anterior chamber in such a way that it can begin to clog the trabecular meshwork (the major site of aqueous humour drainage), which can in turn prevent the aqueous humour from draining and therefore increases the pressure inside the eye. With PDS, the intraocular pressure tends to spike at times and then can return to normal. Exercise has been shown to contribute to spikes in pressure as well. When the pressure is great enough to cause damage to the optic nerve, this is called pigmentary glaucoma. As with all types of glaucoma, when damage happens to the optic nerve fibers, the vision loss that occurs is irreversible and painless.

This condition is rare, but occurs most often in Caucasians, particularly men, and the age of onset is relatively low: mid 20s to 40s. As the crystalline lens hardens with age, the lens zonules pull away from the iris and the syndrome lessens and stops. Most sufferers are nearsighted.

There is no cure yet, but pigmentary glaucoma can be managed with eye drops or treated with simple surgeries. One of the surgeries is the YAG laser procedure in which a laser is used to break up the pigment clogs, and reduce pressure. If caught early and treated, chances of glaucoma are greatly reduced. Sufferers are often advised not to engage in high-impact sports such as long-distance running or martial arts, as strong impacts can cause more pigment cells to slough off.

A 2016 Cochrane Review sought to determine the effectiveness of YAG laser iridotomy versus no laser iridotomy for pigment dispersion syndrome and pigmentary glaucoma, in 195 participants, across five studies. No clear benefits in preventing loss of visual field were found for eyes treated with peripheral laser iridotomy. There was weak evidence suggesting that laser iridotomy could be more effective in lowering intraocular pressure in eyes versus no treatment.

A synechia is an eye condition where the iris adheres to either the cornea (i.e. "anterior synechia") or lens (i.e. "posterior synechia"). Synechiae can be caused by ocular trauma, iritis or iridocyclitis and may lead to certain types of glaucoma. It is sometimes visible on careful examination but usually more easily through an ophthalmoscope or slit-lamp.

Anterior synechia causes closed angle glaucoma, which means that the iris closes the drainage way of aqueous humour which in turn raises the intraocular pressure. Posterior synechia also cause glaucoma, but with a different mechanism. In posterior synechia, the iris adheres to the lens, blocking the flow of aqueous humor from the posterior chamber to the anterior chamber. This blocked drainage raises the intraocular pressure.

Fuchs heterochromic iridocyclitis (FHI) is a chronic unilateral uveitis appearing with the triad of heterochromia, predisposition to cataract and glaucoma, and keratitic precipitates on the posterior corneal surface. Patients are often asymptomatic and the disease is often discovered through investigation of the cause of the heterochromia or cataract. Neovascularisation (growth of new abnormal vessels) is possible and any eye surgery, such as cataract surgery, can cause bleeding from the fragile vessels in the atrophic iris causing accumulation of blood in anterior chamber of the eye, also known as hyphema.

Cycloplegia is paralysis of the ciliary muscle of the eye, resulting in a loss of accommodation. Because of the paralysis of the ciliary muscle, the curvature of the lens can no longer be adjusted to focus on nearby objects. This results in similar problems as those caused by presbyopia, in which the lens has lost elasticity and can also no longer focus on close-by objects. Cycloplegia with accompanying mydriasis (dilation of pupil) is usually due to topical application of muscarinic antagonists such as atropine and cyclopentolate.

Mydriatic/cycloplegic agents, such as topical homatropine, which is similar in action to atropine, are useful in breaking and preventing the formation of posterior synechia by keeping the iris dilated and away from the crystalline lens. Dilation of the pupil in an eye with the synechia can cause the pupil to take an irregular, non-circular shape (Dyscoria) as shown in the photograph. If the pupil can be fully dilated during the treatment of iritis, the prognosis for recovery from synechia is good. This is a treatable status.

To subdue the inflammation, use topical corticosteroids. If the intra-ocular pressure is elevated then use a PGA such as Travatan Z.

The number of cases is around 0.5 to 0.7 per 10,000 births, making it a relatively rare condition.

In segmental heterochromia, sometimes referred to as sectoral heterochromia, areas of the same iris contains two completely different colors.

Segmental heterochromia is rare in humans; it is estimated that only about 1% of the population have it.

Congenital heterochromia is usually inherited as an autosomal dominant trait.

Hemeralopia (from Greek "ημέρα", hemera "day"; and "αλαός", alaos "blindness") is the inability to see clearly in bright light and is the exact opposite of nyctalopia (night blindness). Hemera was the Greek goddess of day and Nyx was the goddess of night. However, it has been used in an opposite sense by many non-English-speaking doctors. It can be described as insufficient adaptation to bright light. It is also called heliophobia and day blindness.

In hemeralopia, daytime vision gets worse, characterised by photoaversion (dislike/avoidance of light) rather than photophobia (eye discomfort/pain in light) which is typical of inflammations of eye. Nighttime vision largely remains unchanged due to the use of rods as opposed to cones (during the day), which are affected by hemeralopia and in turn degrade the daytime optical response. Hence many patients feel they see better at dusk than in daytime.

Miosis is excessive constriction of the pupil. The term is from Ancient Greek , "mūein", "to close the eyes.

The opposite condition, mydriasis, is the dilation of the pupil. Anisocoria is the condition of one pupil being more dilated than the other.

A mydriatic is an agent that induces dilation of the pupil. Drugs such as tropicamide are used in medicine to permit examination of the retina and other deep structures of the eye, and also to reduce painful ciliary muscle spasm (see cycloplegia). Phenylephrine (e.g. Cyclomydril) is used if strong mydriasis is needed for a surgical intervention. One effect of administration of a mydriatic is intolerance to bright light (photophobia). Purposefully-induced mydriasis via mydriatics is also used as a diagnostic test for Horner's syndrome.

While the vast majority of hyphemas resolve on their own without issue, sometimes complications occur. Traumatic hyphema may lead to increased intraocular pressure, peripheral anterior synechiae, atrophy of the optic nerve, staining of the cornea with blood, re-bleeding, and impaired accommodation.

Secondary hemorrhage, or rebleeding of the hyphema, is thought to worsen outcomes in terms of visual function. Rebleeding occurs in 4-35% of hyphema cases and is a risk factor for glaucoma.

Mydriasis () is the dilation of the pupil, usually having a non-physiological cause, or sometimes a physiological pupillary response. Non-physiological causes of mydriasis include disease, trauma, or the use of drugs.

Normally, as part of the pupillary light reflex, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day. A "mydriatic" pupil will remain excessively large even in a bright environment. The excitation of the radial fibres of the iris which increases the pupillary aperture is referred to as a mydriasis. More generally, mydriasis also refers to the natural dilation of pupils, for instance in low light conditions or under sympathetic stimulation.

An informal term for mydriasis is blown pupil, and is used by medical providers. It is usually used to refer to a fixed, unilateral mydriasis, which could be a symptom of raised intracranial pressure.

The opposite, constriction of the pupil, is referred to as miosis. Both mydriasis and miosis can be physiological. Anisocoria is the condition of one pupil being more dilated than the other.

Cycloplegic drugs are generally muscarinic receptor blockers. These include atropine, cyclopentolate, homatropine, scopolamine and tropicamide. They are indicated for use in cycloplegic refraction (to paralyze the ciliary muscle in order to determine the true refractive error of the eye) and the treatment of uveitis. All cycloplegics are also mydriatic (pupil dilating) agents and are used as such during eye examination to better visualize the retina.

When cycloplegic drugs are used as a mydriatic to dilate the pupil, the pupil in the normal eye regains its function when the drugs are metabolized or carried away. Some cycloplegic drugs can cause dilation of the pupil for several days. Usually the ones used by ophthalmologists or optometrists wear off in hours, but when the patient leaves the office strong sunglasses are provided for comfort.

Colobomas can be associated with a mutation in the "PAX2" gene.

Eye abnormalities have been shown to occur in over 90% of children with fetal alcohol syndrome.