View source for Aniridia

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{{Infobox_Disease |
  Name           = {{PAGENAME}} |
  Image          = BlackEyesAniridia.jpg |
  Caption        = Eyes of a Scandinavian male wherein the iris is not present due to aniridia. Notice the lack of common [[eye color]] as the eye appears to be one large pupil. |
  DiseasesDB     = 723 |
  ICD10          = {{ICD10|Q|13|1|q|10}} |
  ICD9           = {{ICD9|743.45}} |
  ICDO           = |
  OMIM           = 106200 |
  OMIM_mult      = {{OMIM2|106210}} |
  MedlinePlus    = |
  MeshID         = D015783 |
}}
{{SI}}
{{CMG}}

{{SK}} Absent iris
==Overview==
'''Aniridia''' is a rare [[congenital]] condition characterized by the underdevelopment of the [[eye]]'s [[iris (anatomy)|iris]]. This usually occurs in both eyes. It is associated with poor development of the [[retina]] at the back of the eye preventing normal vision development.

==Classification==

Aniridia may be broadly divided into hereditary and sporadic forms.  Hereditary aniridia is usually transmitted in an [[autosomal dominant]] manner (each offspring has a 50% chance of being affected), although rarer [[autosomal recessive]] forms (such as Gillespie syndrome) have also been reported.  Sporadic aniridia [[mutations]] may affect the WT1 region adjacent to the AN2 aniridia region, causing a kidney cancer called [[nephroblastoma]] ([[Wilms tumor]]).  These patients often also have genitourinary abnormalities and [[mental retardation]] ([[WAGR syndrome]]).

The AN2 region of the short arm of [[chromosome 11]] (11p13) includes the [[PAX6]] gene (named for its PAired boX status), whose gene product helps regulate a cascade of other genetic processes involved in the development of the eye (as well as other nonocular structures). This PAX6 gene is around 95% similar to the pax gene found in [[zebrafish]], a creature which diverged from the human ancestry around 400 million years ago. Thus, the PAX6 gene constitutes an important [[evolution]]ary link to mankind's distant ancestors.

Defects in the PAX6 gene cause aniridia-like ocular defects in mice (as well as Drosophilia = fruit flies).  Aniridia is a heterozygotic disease, meaning that only one of the two [[chromosome 11]] copies is affected.  When both copies are altered ([[homozygous]] condition), the result is a uniformly fatal condition with near complete failure of entire eye formation. In 2001, two cases of homozygous Aniridia patients were reported; the foetuses died prior to birth and had severe brain damage. In mice, homozygous ''Small eye'' defect (mouse Pax-6) led to loss of eyes, nose and the foetuses suffered severe brain damage.<ref>W. J. Gehring (2001): ''The genetic control of eye development and its implications for the evolution of various eye-types'', Zoology ''104'':171-181</ref>

Several different mutations may affect the PAX6 gene. Some mutations appear to inhibit gene function more than others, with subsequent variability in the severity of the disease. Thus, some aniridic individuals are only missing a relatively small amount of iris, do not have foveal hypoplasia, and retain relatively normal [[Visual perception|vision]].  Presumably, the genetic defect in these individuals causes less "heterozygous insufficiency," meaning they retain enough gene function to yield a milder [[phenotype]].

* {{OMIM|106200}} AN1
* {{OMIM|106210}} AN2
* {{OMIM|106220}} Aniridia and absent patella
* {{OMIM|106230}} Aniridia, microcornea, and spontaneously reabsorbed cataract
* {{OMIM|206700}} Aniridia, cerebellar ataxia, and mental deficiency (Gillespie syndrome)

==Clinical Presentation==
===Ocular===
* Stumps of [[iris (anatomy)|iris]] usually apparent
* Some patients have partial aniridia with relatively preserved vision
* [[Cornea]]l findings; Limbal [[stem cell]] deficiency = aniridic [[keratopathy]]
* Corneal  [[pannus]] usually presents in early childhood with radial vessels at 6 and 12 o’clock, developing circumferential grayish haze which advances centrally
* Corneal [[epithelium]] may harbor ectopic [[conjunctiva]]l [[goblet cells]], and inflammatory cells are usually present 
* Microcornea is very common in aniridia
* Initial fine [[lens (anatomy)|lens]] opacities in infants
* Visually significant [[cataract]] often acquired by 2nd-3rd decade
* Multiple [[cataract]] types described: anterior polar, pyramidal, nuclear, lamellar, and cortical
* Lens subluxation / [[ectopia lentis]]
* [[Nystagmus]]
* Sensory [[strabismus]]
* [[Glaucoma]] onset usually by 2nd decade
* Gradually increasing angle obstruction, though open angle also possible
* Possible [[glaucoma]] mechanism: Contractile membrane covering angle, with increase in iridocorneal processes; iris stump may become totally adherent to posterior corneal surface
* Foveal hypoplasia, which may be complete or very subtle; [[Fluorescein angiography]] may be needed to demonstrate lack of [[fovea]]l avascular zone
* [[Optic nerve hypoplasia]] to some degree is present in up to 75% of aniridia patients

===Non-ocular===
* [[Dysosmia]] / [[dysnomia]] = abnormal sense of smell due to hypoplastic [[olfactory bulb]]s
* [[Glucose]] intolerance / [[diabetes mellitus]]
* Reduced size of [[corpus callosum]] and anterior commissure
* Absent [[pineal gland]]: abnormal [[sleep]] due to [[melatonin]] abnormalities
* Unilateral [[polymicrogyria]]
* [[WAGR syndrome]] ([[Wilms tumor]], aniridia, [[genitourinary]] abnormality, [[mental retardation]])
* [[Wilms tumor]] occurs in 30–50% of cases
* External genital anomalies occur only in males, often delaying recognition of WAGR in females
* Late onset [[nephropathy]] is a well-recognized feature of this syndrome

==Treatment==
Due to the high risk of [[glaucoma]] and [[cataract]] formation, aniridia patients should be under the care of an [[ophthalmologist]] familiar with the condition.  The risk of progressive glaucoma persists from childhood into adulthood, necessitating long-term follow-up. Optometrists and low vision specialists are often valuable in maximizing visual and social functioning, prescribing glasses, and amelioriating light sensitivity ([[photophobia]]).

The iris functions to restrict the amount of light entering the eye, so if it is absent, most individuals with aniridia are sensitive to bright outdoor light and their eyes may need protecting. This can be done with tinted [[glasses]], or with a [[contact lens]] which has an artificial iris painted onto it.

Aniridia is often associated with other health and developmental problems, as well as complicating eye conditions such as: [[foveal hypoplasia]], [[nystagmus]], [[glaucoma]], [[cornea|corneal disease]], [[cataract]], [[subluxation|lens subluxation]] and [[optic nerve]] disease.

==References==
<references/>

==Related Chapters==
*[[WAGR syndrome]]



{{Congenital malformations and deformations of eye, ear, face and neck}}
{{Eye pathology}}
[[Category:Neurology]]
[[Category:Ophthalmology]]
[[Category:Genetics]]
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[[es:Aniridia]]
[[pl:Aniridia]]
[[pt:Aniridia]]

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