Aniridia is a rare ocular condition most often caused by a mutation in the PAX6 gene located on the short arm of chromosome 11.
Aniridia is a rare, panocular, congenital disorder of the tissues of the eye, and results in progressive and severe sight disruption . Characterized by extreme hypoplasia of the iris, aniridia often presents with foveal hypoplasia and nystagmus  . Related ocular conditions including glaucoma, cataracts, strabismus and optic nerve hypoplasia result in a variety of visual problems  .
Aniridia usually presents in infancy , and although wide-ranging cerebral defects have been shown , hearing and olfactory abnormalities are the most common associated functional deficits . Approximately two-thirds of cases show familial dominant inheritance while the other one-third are sporadic . Sporadic aniridia may show only ocular abnormality, or present in association with a number of systemic disorders . The most common of these is WAGR syndrome that describes the association with Wilms tumor, urogenital abnormalities and mental retardation  .
All patients have reduced visual function, and regular monitoring is required for early management of a range of debilitating long-term outcomes . Due to the inheritance pattern, genetic counselling is appropriate .
Haploinsufficiency of the PAX6 gene is detectable in about 90% of cases, resulting from genic mutations in two-thirds and chromosomal rearrangements in one-third of cases . Both copies of this gene are required for normal eye development, as it regulates genesis of most of the ocular tissues. PAX6 also regulates development of the olfactory bulb, multiple regions throughout the brain, the gut, pancreas and neural tube  .
The incidence of aniridia has been reported between 1:40 000 to 1:100 000  and no significant gender or racial bias has been shown . Familial cases of aniridia with dominant inheritance account for approximately two-thirds of patients, with almost complete penetration but variable phenotype . The remaining one-third are sporadic cases  .
The pathophysiology underlying aniridia is not known with certainty . The epithelium of the normal iris derives from the neuroectoderm of the anterior rim of the optic cup, while the stroma is derived from the mesenchymal tissue of the neural crest . Both stroma and epithelium are deficient in aniridia so defects in the development of either tissue may prevent normal maturation of the other . Another theory suggests that aniridia may result from excessive remodelling, with regular iris formation being followed by inappropriate iris tissue regression .
Even with early diagnosis and proper management, aniridia has a poor visual prognosis.
Renal ultrasounds are indicated up to 8 years of age for children exhibiting WAGR or sporadic aniridia without chromosomal abnormality . Cytogenetic testing is used to detect chromosomal abnormalities . The severity of ocular involvement can be assessed by measuring visual acuity, and ophthalmoscopy used to determine iris/pupil abnormalities, optic nerve/foveal hypoplasia and the presence of glaucoma or cataracts  .
A lifelong combination of medical and surgical treatment is required to control intraocular pressure . Medical treatment can involve the use of topical miotics, carbonic anhydrase inhibitors and sympathomimetics  . Surgical treatments include the following: goniotomy, trabeculectomy with or without antimetabolites, filtration procedures and trabeculoplasty, but no one treatment has been reliable or shown high efficacy  .
The treatment approach depends on the degree of keratopathy of the ocular surface . Mucolytics, lubricants and drops without preservatives have been shown to be useful . Surgical treatments have a poor prognosis  and are reserved for cases with severe reduction of vision . Results of penetrating keratoplasty are very poor , and transplantation of amniotic membrane has shown good but only temporary results . Homologous lamellar limbokeratoplasty has given high success rates due in part to the use of systemic immunosuppressants . Use of the Type 1 Boston keratoprosthesis has been very successful , but the development or worsening of glaucoma after transplantation limits the long-term success .
Severe opacification necessitates extraction  , which may be accompanied by an intraocular lens implant . Surgical improvements to vision are limited by other ocular defects  and postoperative complications including macular oedema and uveitis , determine the surgical technique of choice .
Various techniques have been used to relieve the effects of iris hypoplasia, including contact lenses, eyelid surgery, tattooing of the cornea and implantation of artificial iris devices. The development of silicone implants personalized to the colour of the other eye means they can be inserted via a minimal incision in the cornea .
Nystagmus and photophobia
These can be relieved by the use tinted spectacles, tinted intraocular lenses and tinted contact lenses  .
There are no guidelines for the prevention of this inherited disorder.
Aniridia is a rare genetic eye condition that is present at birth. It typically affects both eyes and occurs in approximately 1 in 60,000 births. Rarely, aniridia is caused by trauma to the eye, or sometimes it is not inherited but develops by chance.
Aniridia results in the incomplete formation of the iris (the coloured part of the eye that surrounds the pupil). Aniridia can also affect other parts of the eye including the retina, the cornea and the lens, and causes a wide variety of visual problems.
Most often, aniridia is inherited and congenital, meaning it is passed from parent to child through their genes and is present at birth. Genes are present in pairs and one of each pair is inherited from each of your parents. A parent can carry one normal and one faulty gene but not develop aniridia because the normal gene makes up for the faulty one. The gene responsible for aniridia is called PAX6. If PAX6 is missing or wrong, it prevents the proper formation of parts of the eye, especially the iris, prior to birth.
Children can inherit genetic conditions through either a dominant or recessive pattern. Dominant conditions are inherited from only one parent. If a parent who carries the aniridia gene has children with a partner who does not carry the gene, there is a 50% chance that any child will have aniridia. A child who does not inherit aniridia cannot pass it on to their children. Nearly two-thirds of congenital cases are caused by a faulty gene inherited this way.
Recessive conditions are inherited from both parents. You would need to inherit the aniridia gene from both parents to develop a recessive type of aniridia. If two parents who carry the gene (but don’t have aniridia) have a child, there is a 25% chance that the child will develop aniridia. Only a very small number of cases of aniridia are caused by a faulty gene inherited this way. Gillespie syndrome is a rare recessive condition that causes aniridia and problems with writing, speech and walking.
Approximately one-third of congenital cases occur spontaneously and are not inherited from either parent. The faulty gene starts for the first time in the affected child, and these children are at risk of developing other associated conditions, WAGR syndrome or Miller syndrome.
WAGR are the initials of the problems that can occur in this syndrome:
W: Wilms Tumour is a childhood tumour involving the kidney that usually develops before age 5.
G: Genitourinary problems.
R: Retardation (Mental).
Boys and girls can develop WAGR Syndrome, and not all children with the syndrome will have the same types of problems.
Miller syndrome can cause cleft palate and other developmental problems with the face and the limbs. For most children, the eyes are the only affected parts of the body.
The symptoms of aniridia are highly variable and depend on which parts of the developing eye are affected, and some conditions may only develop later on. Some of the more common include:
Aniridia is usually picked up by a paediatrician during a routine examination, and the child is referred to an ophthalmologist for proper diagnosis. Blood tests may be taken for genetic screening and confirmation of the diagnosis. Children at risk of developing a Wilms tumor will have a regular abdominal ultrasound at least until they are 10 years old. Wilms tumor can be treated successfully if detected early.
Treatment depends on the type and severity of the problems, and may include: