A third cause of light-near dissociation is Parinaud syndrome, also called dorsal midbrain syndrome. This uncommon syndrome involves vertical gaze palsy associated with pupils that “accommodate but do not react." The causes of Parinaud syndrome include brain tumors (pinealomas), multiple sclerosis and brainstem infarction.

Due to the lack of detail in the older literature and the scarcity of AR pupils at the present time, it is not known whether syphilis can cause Parinaud syndrome. It is not known whether AR pupils are any different from the pupils seen in other dorsal midbrain lesions.

The condition is diagnosed clinically but physician

Argyll Robertson pupils (AR pupils or, colloquially, "prostitute's pupils") are bilateral small pupils that reduce in size on a near object (i.e., they accommodate), but do "not" constrict when exposed to bright light (i.e., they do not react to light). They are a highly specific sign of neurosyphilis; however, Argyll Robertson pupils may also be a sign of diabetic neuropathy. In general, pupils that accommodate but do not react are said to show light-near dissociation (i.e., it is the absence of a miotic reaction to light, both direct and consensual, with the preservation of a miotic reaction to near stimulus (accommodation/convergence).

AR pupils are extremely uncommon in the developed world. There is continued interest in the underlying pathophysiology, but the scarcity of cases makes ongoing research difficult.

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

Use of high doses of opioid drugs such as morphine, oxycodone, heroin, or hydrocodone can cause ptosis. Pregabalin (Lyrica), an anticonvulsant drug, has also been known to cause mild ptosis.

Relative afferent pupillary defect (RAPD) or Marcus Gunn pupil is a medical sign observed during the swinging-flashlight test whereupon the patient's pupils constrict less (therefore appearing to dilate) when a bright light is swung from the unaffected eye to the affected eye. The affected eye still senses the light and produces pupillary sphincter constriction to some degree, albeit reduced.

The most common cause of Marcus Gunn pupil is a lesion of the optic nerve (between the retina and the optic chiasm) or severe retinal disease. It is named after Scottish ophthalmologist Robert Marcus Gunn.

A second common cause of Marcus Gunn pupil is a contralateral optic tract lesion, due to the different contributions of the intact nasal and temporal hemifields.

It most commonly affects younger women (2.6:1 female preponderance) and is unilateral in 80% of cases. Average age of onset is 32 years.

Adie's syndrome is not life-threatening or disabling. As such, there is no mortality rate relating to the condition; however, loss of deep tendon reflexes is permanent and may progress over time.

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

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.

Ptosis occurs due to dysfunction of the muscles that raise the eyelid or their nerve supply (oculomotor nerve for levator palpebrae superioris and sympathetic nerves for superior tarsal muscle). It can affect one eye or both eyes and is more common in the elderly, as muscles in the eyelids may begin to deteriorate. One can, however, be born with ptosis. Congenital ptosis is hereditary in three main forms. Causes of congenital ptosis remain unknown. Ptosis may be caused by damage/trauma to the muscle which raises the eyelid, damage to the superior cervical sympathetic ganglion or damage to the nerve (3rd cranial nerve (oculomotor nerve)) which controls this muscle. Such damage could be a sign or symptom of an underlying disease such as diabetes mellitus, a brain tumor, a pancoast tumor (apex of lung) and diseases which may cause weakness in muscles or nerve damage, such as myasthenia gravis or Oculopharyngeal muscular dystrophy. Exposure to the toxins in some snake venoms, such as that of the black mamba, may also cause this effect.

Ptosis can be caused by the aponeurosis of the levator muscle, nerve abnormalities, trauma, inflammation or lesions of the lid or orbit. Dysfunctions of the levators may occur as a result of autoimmune antibodies attacking and eliminating the neurotransmitter.

Ptosis may be due to a myogenic, neurogenic, aponeurotic, mechanical or traumatic cause and it usually occurs isolated, but may be associated with various other conditions, like immunological, degenerative, or hereditary disorders, tumors, or infections

Acquired ptosis is most commonly caused by aponeurotic ptosis. This can occur as a result of senescence, dehiscence or disinsertion of the levator aponeurosis. Moreover, chronic inflammation or intraocular surgery can lead to the same effect. Also, wearing contact lenses for long periods of time is thought to have a certain impact on the development of this condition.

Congenital neurogenic ptosis is believed to be caused by the Horner syndrome. In this case, a mild ptosis may be associated with ipsilateral ptosis, iris and areola hypopigmentation and anhidrosis due to the paresis of the Mueller muscle. Acquired Horner syndrome may result after trauma, neoplastic insult, or even vascular disease.

Ptosis due to trauma can ensue after an eyelid laceration with transection of the upper eyelid elevators or disruption of the neural input.

Other causes of ptosis include eyelid neoplasms, neurofibromas or the cicatrization after inflammation or surgery. Mild ptosis may occur with aging.

A drooping eyelid can be one of the first signals of a third nerve palsy due to a cerebral aneurysm, that otherwise is asymptomatic and referred to as an oculomotor nerve palsy.

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.

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.

According to an American study nearly three in 10 children (28.4%) between the ages of five and 17 have astigmatism. A recent Brazilian study found that 34% of the students in one city were astigmatic. Regarding the prevalence in adults, a recent study in Bangladesh found that nearly 1 in 3 (32.4%) of those over the age of 30 had astigmatism.

A Polish study published in 2005 revealed "with-the-rule astigmatism" may lead to the onset of myopia.

A number of studies have found the prevalence of astigmatism increases with age.

The Marcus Gunn pupil is a relative afferent pupillary defect indicating a decreased pupillary response to light in the affected eye.

In the swinging flashlight test, a light is alternately shone into the left and right eyes. A normal response would be equal constriction of both pupils, regardless of which eye the light is directed at. This indicates an intact direct and consensual pupillary light reflex. When the test is performed in an eye with an afferent pupillary defect, light directed in the affected eye will cause only mild constriction of both pupils (due to decreased response to light from the afferent defect), while light in the unaffected eye will cause a normal constriction of both pupils (due to an intact efferent path, and an intact consensual pupillary reflex). Thus, light shone in the affected eye will produce less pupillary constriction than light shone in the unaffected eye.

A Marcus Gunn pupil is distinguished from a total CN II lesion, in which the affected eye perceives "no" light. In that case, shining the light in the affected eye produces no effect.

Anisocoria is absent. A Marcus Gunn pupil is seen, among other conditions, in optic neuritis. It is also common in retrobulbar optic neuritis due to multiple sclerosis but only for 3–4 weeks, until the visual acuity begins to improve in 1–2 weeks and may return to normal.

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.

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.

A spasm of accommodation (also known as a ciliary spasm, an accommodation, or accommodative spasm) is a condition in which the ciliary muscle of the eye remains in a constant state of contraction. Normal accommodation allows the eye to "accommodate" for near-vision. However in a state of perpetual contraction, the ciliary muscle cannot relax when viewing distant objects. This causes vision to blur when attempting to view objects from a distance. This may cause pseudomyopia or latent hyperopia.

Although antimuscarinic drops (homoatropine 5%) can be applied topically to relax the muscle, this leaves the individual without any accommodation and, depending on refractive error, unable to see well at near distances. Also, excessive pupil dilation may occur as an unwanted side effect. This dilation may pose a problem since a larger pupil is less efficient at focusing light (see pupil, aperture, and optical aberration for more.)

Patients who have accommodative spasm may benefit from being given glasses or contacts that account for the problem or by using vision therapy techniques to regain control of the accommodative system..

Possible clinical findings include:

Normal Amplitude of accommodation and Near point of convergence

Reduced Negative relative accommodation

Difficulty clearing plus on facility testing

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.

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.

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.

When detected during childhood, without any other symptoms and when other disorders are discarded through clinical tests, it should be considered a developmental or genetic phenomenon.

Asymmetric pupil or dyscoria, potential causes of anisocoria, refer to an abnormal shape of the pupil which can happens due to developmental and intrauterine anomalies.

Parinaud's Syndrome results from injury, either direct or compressive, to the dorsal midbrain. Specifically, compression or ischemic damage of the mesencephalic tectum, including the superior colliculus adjacent oculomotor (origin of cranial nerve III) and Edinger-Westphal nuclei, causing dysfunction to the motor function of the eye.

Classically, it has been associated with three major groups:

1. Young patients with brain tumors in the pineal gland or midbrain: pinealoma (intracranial germinomas) are the most common lesion producing this syndrome.

2. Women in their 20s-30s with multiple sclerosis

3. Older patients following stroke of the upper brainstem

However, any other compression, ischemia or damage to this region can produce these phenomena: obstructive hydrocephalus, midbrain hemorrhage, cerebral arteriovenous malformation, trauma and brainstem toxoplasmosis infection. Neoplasms and giant aneurysms of the posterior fossa have also been associated with the midbrain syndrome.

Vertical supranuclear ophthalmoplegia has also been associated with metabolic disorders, such as Niemann-Pick disease, Wilson's disease, kernicterus, and barbiturate overdose.

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.

The eye findings of Parinaud's Syndrome generally improve slowly over months, especially with resolution of the causative factor; continued resolution after the first 3–6 months of onset is uncommon. However, rapid resolution after normalization of intracranial pressure following placement of a ventriculoperitoneal shunt has been reported.

Treatment is primarily directed towards etiology of the dorsal midbrain syndrome. A thorough workup, including neuroimaging is essential to rule out anatomic lesions or other causes of this syndrome. Visually significant upgaze palsy can be relieved with bilateral inferior rectus recessions. Retraction nystagmus and convergence movement are usually improved with this procedure as well.

The main characteristic that distinguishes physiological anisocoria is an increase of pupil size with lower light or reduced illumination, such that the pupils differ in size between the two eyes. At any given eye examination, up to 41% of healthy patients can show an anisocoria of 0.4 mm or more at one time or another. It can also occur as the difference between both pupils varies from day to day. A normal population survey showed that during poor light or near dark conditions, differences of 1 mm on average between pupils was found.

The presence of physiologic anisocoria has been estimated at 20% of the normal population, so some degree of pupil difference may be expected in at least 1 in 5 clinic patients.