Aniridia

Aniridia is marked by the partial or complete absence of the iris of the eye. Vision is preserved in some patients with mild? cases of aniridia. This condition occurs when the iris fails to develop normally before birth in one or both eyes. Typically, aniridia can be seen from birth. Aniridia can occur as a single abnormality or can be one of many symptoms of an underlying condition.

Isolated aniridia: Isolated aniridia is the partial or complete absence of the iris from birth. Some people with this type of aniridia may be unaware of any eye problems because pupils appear normal and usually only one eye is mildly affected. In more severe? cases, isolated aniridia can cause vision problems later in life. Accompanying symptoms may include clouding of the crystalline lens of the eye (cataracts) and gradual loss of vision due to increased pressure inside the eyeball which may be accompanied by varying degrees of pain (glaucoma) or superficial clouding of the cornea (corneal pannus). Rapid involuntary movement of the eyeball (nystagmus) and underdevelopment of the fovea area of the retina? (which controls acute? vision) may also occur. These accompanying symptoms can make vision cloudy or blurry.

Gillespie syndrome: Symptoms of Gillespie syndrome include aniridia, intellectual disability, and ataxia (lack of coordination of muscle movements). (For more information choose “Gillespie” as your search term in the Rare Disease Database.)

WAGR syndrome: WAGR stands for Wilms’ tumor (a type of kidney? tumor), Aniridia, Genitourinary abnormalities, and Retardation (now called “Intellectual disability”). WAGR syndrome can also be associated with obesity. WAGR syndrome can present with some or all of these symptoms. (For more information choose “Wilms” as your search term in the Rare Disease Database.)

Diagnosis

The patients usually complain of photophobia? related to the severity of aniridia and poor vision (due to many reasons, including foveal hypoplasia and optic nerve head hypoplasia) since early childhood. Parents may bring a child with the abnormal appearance of the eyes.

Nystagmus and strabismus are common due to poor vision since childhood.

Other ocular findings include:

• Aniridia- The iris may be partially absent (detectable with retro illumination), or there may be a complete absence of iris on external observation. However, most cases have small hypoplastic iris tissue visible on gonioscopy. All cases have some hypoplastic iris tissue on histopathological examination.[rx] Thus, the term aniridia is a misnomer, and ‘iridemia’ may be a better term to describe the disease. There may be iris coloboma, corectopia (eccentric pupil), and loss of crypts of the iris.
• Bilateral? ptosis
• Meibomian gland dysfunction
• Aniridia-associated keratopathy (AAK)- There is limbal stem cell deficiency, corneal pannus, corneal epithelial irregularity, and conjunctivalization of the cornea. Corneal opacity, corneal scarring (subepithelial fibrosis), and vascularization are seen peripherally and may encroach the central cornea. Corneal portends a bad prognosis after penetrating keratoplasty and predisposes to graft rejection and failure. There is dry eye and tear film instability. The ocular surface may be very poor and unstable predisposing to epithelial defect and/or infective keratitis. A classification of AAK into three stages (mild, moderate, and severe limbal insufficiency) has been suggested.[rx][rx]
• Microcornea
• Glaucoma – The corneal thickness is usually high, which might influence the measurement of the intraocular pressure. In the early years of life, the angle of the anterior chamber is generally open on gonioscopy, and congenital glaucoma/buphthalmos is rare in aniridia. However, within 2nd-decade angle closure due to peripheral anterior synechia is noted, which may lead to an increase in the intraocular pressure.
• Persistent pupillary membrane
• Rudimentary iris stump on gonioscopy – Gonioscopy may show iris fibers that lie in the space between the rudimentary small hypoplastic iris and the trabecular meshwork. These fibers contract and pull the rudimentary iris forward thereby causing synechiae angle-closure glaucoma
• Superior subluxation of the lens (clear or cataractous), ectopia lentis (noted in up to 56% of cases),[rx] dislocation of the lens
• Cataracts or opacities of the crystalline lens or its capsule may be present in 50% to 85% of patients.[rx]
• Microspherophakia
• Optic nerve head hypoplasia is present in 75% of cases in a series of 12 patients with aniridia.[rx] A reduced disc diameter may confirm the hypoplasia: width of the retinal arteriole at the disc margin of 6.1 to less than 14.6 (normal value 14.6 ± 2.4)[rx]
• Foveal hypoplasia – Foveal hypoplasia, is characterized by the absence of a defined foveal avascular zone, the absence of pigmentation at the fovea and blood vessels may cross through the area where the fovea is presumed to be present. Foveal depression is absent, and inner retinal layers are present all over the macular region. In a normal fovea, inner retinal layers are absent, and there is a depression corresponding to the foveola.
• Fundal coloboma
• Aniridic fibrosis syndrome[rx]– ‘A progressive anterior fibrosis syndrome in patients with postsurgical congenital aniridia’ has been described. Usually, there is a history of multiple surgeries, including cataract surgery, glaucoma surgery, and keratoplasty. This condition is characterized by retrocorneal and retroarticular membranes arising from the rudimentary iris, which may involve ciliary processes and the anterior retina also. This progressive membrane results in anterior displacement of the intraocular lens and corneal decompensation.

• Sensory deficiency including

  • Abnormal olfaction
  • Hearing loss[rx]
• AGR triad (aniridia, genitourinary abnormalities, mental retardation)
• Absent or hypoplastic patella (OMIM 106220, aniridia, and absent patella) in family

Imaging findings

• Optical coherence tomography (OCT) may be used to document foveal hypoplasia. Although OCT is difficult to perform in the presence of nystagmus, useful images can be obtained with persistence. This should be routinely performed to support a clinical diagnosis, especially where iris defects may be subtle. Anterior segment OCT can also be used to delineate the detailed anatomy of the anterior segment structures, even in those with corneal opacity [Majander et al 2012].
• Ultrasound B-scan should be performed routinely to assess axial length due to the association with microphthalmia.
• High-frequency ultrasound biomicroscopy. In infants with corneal opacity or severe corneal edema resulting from associated congenital glaucoma, high-frequency anterior segment ultrasound examination, usually performed under anesthesia, can demonstrate iris hypoplasia and/or absence [Nischal 2007].