An iris cyst, or uveal cyst, is a small hollow structure either attached to the iris of the eye or floating free in the anterior chamber. An iris cyst is composed of a single cell layer of epithelium and is filled with fluid. It is most commonly seen as secondary to inflammation in the eye, especially with canine glaucoma. They are most commonly seen in dogs. Golden Retrievers, Labrador Retrievers, and Boston Terriers are the most commonly affected breeds. Iris cysts also occur in cats and horses. The cysts are usually free floating in dogs, attached to the pupillary margin in cats, and present in the interior of the iris (especially blue irises) in horses.

Iris cysts usually cause no symptoms, but in large numbers they can cause glaucoma by obstructing the drainage angle of the eye. Golden Retrievers may have a higher rate of glaucoma associated with iris cysts.

Iris cysts need to be differentiated from iris melanoma, a tumor, by demonstrating their hollowness. A light directed at an iris cyst will cause it to transilluminate. Iris cysts can be collapsed if necessary by a veterinarian with a small needle carefully introduced into the anterior chamber. The cysts may also be destroyed by use of a semiconductor diode laser.

Measurement of the degree of exophthalmos is performed using an exophthalmometer.

Most sources define exophthalmos/proptosis as a protrusion of the globe greater than 18 mm.

The term exophthalmos is often used when describing proptosis associated with Graves' disease.

Exophthalmos (also called exophthalmus, exophthalmia, proptosis, or exorbitism) is a bulging of the eye anteriorly out of the orbit. Exophthalmos can be either bilateral (as is often seen in Graves' disease) or unilateral (as is often seen in an orbital tumor). Complete or partial dislocation from the orbit is also possible from trauma or swelling of surrounding tissue resulting from trauma.

In the case of Graves' disease, the displacement of the eye is due to abnormal connective tissue deposition in the orbit and extraocular muscles which can be visualized by CT or MRI.

If left untreated, exophthalmos can cause the eyelids to fail to close during sleep leading to corneal dryness and damage. Another possible complication would be a form of redness or irritation called "Superior limbic keratoconjunctivitis", where the area above the cornea becomes inflamed as a result of increased friction when blinking. The process that is causing the displacement of the eye may also compress the optic nerve or ophthalmic artery, leading to blindness.

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.

Symptoms range from dry eye, epiphora, and irritation, to localized pain, foreign body sensation, subconjunctival hemorrhage, and ulceration. Symptoms are often made worse by vigorous blinking. Diagnosis can be made under a slit lamp upon the observation of redundant conjunctival folds. These folds can be made more apparent by staining with fluorescin dye and by applying gentle upward pressure with a finger to the eyeball through the lower lid. A tear-clearance test can also detect irregularities in the tear-film.

Polycoria is a pathological condition of the eye characterized by more than one pupillary opening in the iris. It may be congenital or result from a disease affecting the iris.

Polycoria is extremely rare, and other conditions are frequently mistaken for it.

Persistent pupillary membrane (PPM) is a condition of the eye involving remnants of a fetal membrane that persist as strands of tissue crossing the pupil. The pupillary membrane in mammals exists in the fetus as a source of blood supply for the lens. It normally atrophies from the time of birth to the age of four to eight weeks. PPM occurs when this atrophy is incomplete. It generally does not cause any symptoms. The strands can connect to the cornea or lens, but most commonly to other parts of the iris. Attachment to the cornea can cause small corneal opacities, while attachment to the lens can cause small cataracts. Using topical atropine to dilate the pupil may help break down PPMs.

In dogs, PPM is inherited in the Basenji but can occur in other breeds such as the Pembroke Welsh Corgi, Chow Chow, Mastiff, and English Cocker Spaniel. It is also rarely seen in cats, horses, and cattle.

With anterior lens luxation, the lens pushes into the iris or actually enters the anterior chamber of the eye. This can cause glaucoma, uveitis, or damage to the cornea. Uveitis (inflammation of the eye) causes the pupil to constrict (miosis) and trap the lens in the anterior chamber, leading to an obstruction of outflow of aqueous humour and subsequent increase in ocular pressure (glaucoma). Better prognosis is valued in lens replacement surgery (retained vision and normal intraocular pressure) when it is performed before the onset of secondary glaucoma. Glaucoma secondary to anterior lens luxation is less common in cats than dogs due to their naturally deeper anterior chamber and the liquification of the vitreous humour secondary to chronic inflammation. Anterior lens luxation is considered to be an ophthalmological emergency.

Lens subluxation is also seen in dogs and is characterized by a partial displacement of the lens. It can be recognized by trembling of the iris (iridodonesis) or lens (phacodonesis) and the presence of an aphakic crescent (an area of the pupil where the lens is absent). Other signs of lens subluxation include mild conjunctival redness, vitreous humour degeneration, prolapse of the vitreous into the anterior chamber, and an increase or decrease of anterior chamber depth. Removal of the lens before it completely luxates into the anterior chamber may prevent secondary glaucoma. A nonsurgical alternative involves the use of a miotic to constrict the pupil and prevent the lens from luxating into the anterior chamber.

Conjunctivochalasis is a common eye surface condition characterized by the presence of excess folds of the conjunctiva located between the globe of the eye and the eyelid margin.

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

Keratoglobus (from Greek: "kerato-" horn, cornea; and Latin: "globus" round), is a degenerative non-inflammatory disorder of the eye in which structural changes within the cornea cause it to become extremely thin and change to a more globular shape than its normal gradual curve. It causes corneal thinning, primarily at the margins, resulting in a spherical, slightly enlarged eye.

It is sometimes equated with "megalocornea".

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.

Keratoglobus is a little-understood disease with an uncertain cause, and its progression following diagnosis is unpredictable. If afflicting both eyes, the deterioration in vision can affect the patient's ability to drive a car or read normal print. It does not however lead to blindness per se.

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.

Leukocoria (also leukokoria or white pupillary reflex) is an abnormal white reflection from the retina of the eye. Leukocoria resembles eyeshine, but leukocoria can occur in humans and other animals that lack eyeshine because their retina lacks a "tapetum lucidum".

Leukocoria is a medical sign for a number of conditions, including Coats disease, congenital cataract, corneal scarring, melanoma of the ciliary body, Norrie disease, ocular toxocariasis, persistence of the tunica vasculosa lentis (PFV/PHPV), retinoblastoma, and retrolental fibroplasia.

Because of the potentially life-threatening nature of retinoblastoma, a cancer, that condition is usually considered in the evaluation of leukocoria. In some rare cases (1%) the leukocoria is caused by Coats' disease (leaking retinal vessels).

Telecanthus (from the Greek word "tele" (τῆλε) meaning far, and the Latin word canthus, meaning either corner of the eye, where the eyelids meet) refers to increased distance between the medial canthi of the eyes, while the inter-pupillary distance is normal. This is in contrast to hypertelorism, where the inter-pupillary distance is increased.

The distance between the inner corner of the left eye and the inner corner of the right eye, is called intercanthal distance. In most people, the intercanthal distance is equal to the distance between the inner corner and the outer corner of each eye, that is, the width of the eye. The average interpupillary distance is 60–62 millimeters (mm), which corresponds to an intercanthal distance of approximately 30–31 mm. The situation, where intercanthal distance is intensely bigger than the width of the eye, is called telecanthus (tele= Greek τηλε = far, and Greek ακανθα = thorn). This can be an ethnic index or an indication for hypertelorism or hypotelorism, if it is combined with abnormal relation to the interpupillary distance (A D STEAS).

"Traumatic Telecanthus" refers to telcanthus resulting from traumatic injury to the nasal-orbital-ethmoid (NOE) complex. The diagnosis of traumatic telecanthus requires a measurement in excess of those normative values. The pathology can be either unilateral or bilateral, with the former more difficult to measure.

On photographs taken using a flash, instead of the familiar red-eye effect, leukocoria can cause a bright white reflection in an affected eye. Leukocoria may appear also in low indirect light, similar to eyeshine.

Leukocoria can be detected by a routine eye exam (see Ophthalmoscopy). For screening purposes, the red reflex test is used. In this test, when a light is shone briefly through the pupil, an orange red reflection is normal. A white reflection is leukocoria.

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.

Vitreous touch syndrome, also known as vitreous wick syndrome is a late complication of intra capsular cataract extraction wherein the vitreous bulges through the pupillary aperture, and touches and attaches to the corneal endothelium.

Telecanthus is often associated with many congenital disorders. Congenital disorders such as Down syndrome, fetal alcohol syndrome, Cri du Chat syndrome, Klinefelter syndrome, Turner syndrome, Ehlers-Danlos syndrome, Waardenburg syndrome often present with prominent epicanthal fold and if these folds are nasal (most commonly are) they will cause telecanthus.

Fig of the used terms

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.

Thyroglossal duct cysts most often present with a palpable asymptomatic midline neck mass above the level of the hyoid bone. The mass on the neck moves during swallowing or on protrusion of the tongue because of its attachment to the tongue via the tract of thyroid descent. Some patients will have neck or throat pain, or dysphagia.

The persistent duct or sinus can promote oral secretions, which may cause cysts to become infected. Up to half of thyroglossal cysts are not diagnosed until adult life. The tract can lie dormant for years or even decades, until some kind of stimulus leads to cystic dilation. Infection can sometimes cause the transient appearance of a mass or enlargement of the cyst, at times with periodic recurrences. Spontaneous drainage may also occur. Differential diagnosis are ectopic thyroid, enlarged lymph nodes, dermoid cysts and goiter.

Thyroglossal cyst usually presents as a midline neck lump (in the region of the hyoid bone) that is usually painless, smooth and cystic, though if infected, pain can occur. There may be difficulty breathing, dysphagia (difficulty swallowing), or dyspepsia (discomfort in the upper abdomen), especially if the cyst becomes large.

The most common location for a thyroglossal cyst is midline or slightly off midline, between the isthmus of the thyroid and the hyoid bone or just above the hyoid bone. A thyroglossal cyst can develop anywhere along a thyroglossal duct, though cysts within the tongue or in the floor of the mouth are rare.A thyroglossal cyst will move upwards with protrusion of the tongue.Thyroglossal cysts are associated with an increased incidence of ectopic thyroid tissue. Occasionally, a lingual thyroid can be seen as a flattened strawberry-like lump at the base of the tongue.

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

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.