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Ophthalmology > IRIS AND CILIARY BODY
Aniridia
Article Last Updated: Jan 17, 2008
AUTHOR AND EDITOR INFORMATION
Section 1 of 10  
Author: Daljit Singh, MBBS, MS, DSc, Professor Emeritis, Department of Ophthalmology, Guru Nanak Dev University, Amritsar, India; Director, Daljit Singh Eye Hospital
Daljit Singh is a member of the following medical societies: All India Ophthalmological Society, American Society of Cataract and Refractive Surgery, Indian Medical Association, International Intraocular Implant Club, and Intraocular Implant and Refractive Society, India
Coauthor(s):
Arun Verma, MD, Senior Consultant, Department of Ophthalmology, Daljit Singh Eye Hospital, Amritsar, India
Editors: Richard W Allinson, MD, Associate Professor, Division of Ophthalmology, Texas A&M University Health Science Center, Associate Professor, Department of Surgery, Scott and White Clinic; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; J James Rowsey, MD, Former Director of Corneal Services, St Luke's Cataract and Laser Institute, Florida; Lance L Brown, OD, MD, Ophthalmologist, Affiliated With Freeman Hospital and St John's Hospital, Regional Eye Center, Joplin, Missouri; Hampton Roy Sr, MD, Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences
Author and Editor Disclosure
Synonyms and related keywords:
absence of iris, partial or complete absence of iris, congenital aniridia, iridemia, iris hypoplasia, panocular disorder, cataract
Background
Aniridia is a congenital, hereditary, bilateral, extreme form of iris hypoplasia that may be associated with other ocular defects. It describes an extreme form of iris hypoplasia in which the iris appears absent on superficial clinical examination. However, gonioscopy shows the presence of the iris root. Aniridia is not just an isolated defect in iris development but is a panocular disorder with macular and optic nerve hypoplasia, cataract, and corneal changes that are other anomalies that lead to decreased vision and nystagmus. Visual acuity is generally low but is unrelated to the degree of iris hypoplasia. Glaucoma is a secondary problem causing additional visual loss over time. Patients with aniridia usually lack a foveal reflex, indicating poor macular development. True aplasia of the optic nerve also can occur. All these patients need specialized management of each individual problem. Because of poor visual acuity and nystagmus, low vision aids are very helpful. Lifelong regular follow-up care is necessary for the early detection of any new problems, especially glaucoma, lens, and systemic problems, so that timely treatment is given. Since the condition has a dominant transmission, proper genetic counseling should be obtained. Clinical manifestation
- Aniridia alone
- Aniridia in association with systemic defects
- Wilms tumor (20% of cases)
- Genitourinary abnormalities
- Mental retardation
- Aniridia in association with ocular defects
- Albinism
- Ectopia lentis (50%)
- Spontaneous lens dislocation
- Arcus juvenilis
- Keratoconus
- Cataract (50-85%)
- Glaucoma (30-50%)
- Nystagmus
- Strabismus
- Optic nerve hypoplasia (75%)
Pathophysiology
The pathogenesis of aniridia is attributed to a primary developmental arrest of the neuroectoderm and a secondary alteration of all 3 neural crest waves of the mesenchyme. The functional development of the anterior segment is a complex interrelationship between the neural ectoderm and the neural crest waves of the mesenchyme. The pathogenesis may involve defective formation or excessive regression of various layers of the anterior segment caused by cellular or biochemical aberrations. This explains the combined anterior and posterior segment neural ectodermal and mesenchymal defects. The iris stroma is hypoplastic, indicating an altered third neural crest wave of mesenchyme. Aniridia occurs as the following:
- Autosomal disorder
- An identifiable chromosome deletion of the short arm of chromosome 11, including band p13
- Sporadic case
The exact defect in iris morphogenesis giving rise to aniridia is unknown. Because the iris pigment epithelium, the iris musculature, the retina, and the optic nerve are derived from neuroectoderm, there may be a common embryologic origin for these anomalies. As an isolated ocular malformation, aniridia is an autosomal dominant disorder, which is caused by a mutation in the PAX6 (paired box gene family) gene. Patients with aniridia who have a positive family history are not at an increased risk for Wilms tumor. Two genetic loci for aniridia have been identified: one (AN1) on chromosome arm 2p and one (AN2) on chromosome 11. Patients with aniridia without a positive family history have a 30% chance of developing Wilms tumor, and they represent new mutations for the autosomal dominant gene. About one third of such patients have a mutation that affects the WT and AN2 loci, causing the patient to develop Wilms tumor; the other two thirds of patients have a mutation of just the AN2 locus. Because of the high mortality from Wilms tumor, those patients with the WT and AN2 mutations have a low probability of reproducing, whereas those with just AN2 mutations have normal fertility and, hence, a 50% risk to pass the aniridia gene mutation to each child.
Frequency
United States
At present, aniridia strikes 1 in 60,000 individuals; in Canada, this would represent only 475 individuals based on a present population of 28.5 million. In the United States, studies have shown the incidence to be 1 in 90,000. Based on a population of 265 million, this would represent 2945 people.
International
Aniridia is rare and has an incidence of 1 per 64,000 to 1 per 96,000 live births. About two thirds of these cases are familial.
Mortality/Morbidity
All patients with aniridia are visually handicapped for a lifetime. This already reduced vision is threatened further by such complications as cataract and glaucoma. Those patients with Wilms tumor have a reduced span of life.
Race
No racial predisposition exists.
Age
- Congenital glaucoma and aniridia usually are not associated at birth. The glaucoma develops at either the preteen or the teenage level.
- Significant cataracts may occur before puberty. The risk for cataract increases with age, with lens opacities observed in 50-85% of patients during the first 2 decades of life.
History
- The history is straightforward. The condition is discovered early in life, especially in whites. In blacks, the condition might remain undiscovered for a long time until an ophthalmologist examines the eyes for visual problems. The patient presents with the following problems:
- Absence of iris
- Nystagmus
- Strabismus
- Reduced vision
- Thorough family history
- Specific inquiry about any ocular abnormality and/or low vision
- Dental anomaly
- Protruding umbilicus
- Genitourinary abnormalities (Wilms tumor)
- Mental retardation
- Thorough systemic examination of the patient
Physical
A detailed ocular examination is sometimes difficult because of photophobia and nystagmus. If slit lamp flash pictures are taken, they can provide detailed information on corneal opacities and blood vessels, the depth of the anterior chamber, the edge of a transparent dislocated lens, the presence or absence of zonular fibers, and the presence of lenticular opacities. Photographs are useful to observe changes in the tissues with the passage of time. A picture session is especially important in children. The patient might show the following findings: - Nystagmus
- Strabismus
- Photophobia
- Cornea
- Pannus
- Epithelial ulcers
- Aniridic keratopathy
- Arcus juvenilis
- Microcornea
- Anterior chamber
- Best judged with a slit lamp microscope
- Configuration dependent upon the position of the crystalline lens
- Iris
- Complete absence of iris on oblique illumination
- Hypoplasia with irregular pupillary margins (atypical coloboma of pupil)
- Root of the iris visible on gonioscopy
- Angle of the anterior chamber - Trabecular meshwork may be partially or completely covered by the iris stump.
- Crystalline lens
- Transparent or opaque
- Ectopia lentis
- Completely dislocated lens
- Vitreous - Usually normal
- Fundus
- Optic nerve hypoplasia
- Macular reflex dull
- Glaucomatous cupping
- Intraocular pressure
- Vision - Usually about 20/200 or less
Causes
Aniridia is caused by the following:
- An identifiable chromosome deletion of the short arm of chromosome 11, including band p13.
- Patients with aniridia who have a positive family history: Two genetic loci for aniridia have been identified, one (AN1) on chromosome arm 2p and one (AN2) on chromosome 11.
- As an isolated ocular malformation, aniridia is an autosomal dominant disorder, which is caused by a mutation in the PAX6 (paired box gene family) gene.
Other Problems to be Considered
Rieger syndrome with iridocorneal dysgenesis
Congenital coloboma of the iris
Hereditary iris hypoplasia
Traumatic iris injury
Surgical iris coloboma
Bilateral congenital mydriasis
AGR triad - Sporadic (bilateral or unilateral) aniridia, genitourinary abnormalities, and mental retardation
Lab Studies
- Chromosomal deletion is detected by cytogenetic testing with the use of high-resolution banding.
- Submicroscopic deletions of the Wilms tumor gene are recognized with a fluorescent in situ hybridization (FISH) technique.
- High-resolution chromosome studies are obtained in sporadic cases to determine if there is a deletion of band 11p13.
- Serial renal ultrasound examinations are indicated in patients through age 7 years, especially for those with a deletion of band 11p13 or for those with a negative family history of aniridia and normal chromosomes.
Histologic Findings
Histologically, small portions of the iris are always present; the ciliary body is usually hypoplastic; and the anterior chamber angle may be normal, immature (ie, incompletely developed), or malformed. In eyes enucleated from older patients, extensive peripheral anterior synechiae that cause the iris stump to adhere to the posterior corneal surface have been observed.
Medical Care
- Prophylaxis is directed toward the prevention of glaucoma, which includes the following:
- Medical treatment with miotics
- Surgical separation of the iris from the trabecular meshwork in selected cases
- The medical treatment is directed toward control of intraocular pressure, which includes the topical use of the following:
- Miotics
- Beta-blockers
- Sympathomimetics
- Carbonic anhydrase inhibitors
- Prostaglandin analogues
- The chances of failure with local antiglaucoma treatment are high.
- Treatment of photophobia and nystagmus
- Tinted or iris contact lenses
- Tinted spectacle lenses
- Tinted intraocular lenses (IOLs)
- By the above measures, reducing the amplitude and frequency of nystagmus is possible.
- Treatment of refractive errors - Careful refraction and complete correction
- Treatment of amblyopia and strabismus
- Usually, the potential visual acuity in both eyes should be symmetrical.
- When the vision is unequal without structural difference, vigorous amblyopia exercises should be performed in the worst eye.
- Binocularity can be achieved if macular hypoplasia is not severe.
- Strabismus surgery is indicated at an early age.
Surgical Care
- Management of corneal opacification
- Keratoplasty
- Keratoprosthesis
- Management of cataract
- In-the-bag lens implantation in cases without lens dislocation
- Use of opaque intracapsular rings to produce an artificial pupil or use of a large intraocular lens with a clear central optic and an opaque periphery
- In-the-bag IOL placement with intracapsular rings, when there is slight lens displacement
- Lens extraction followed by contact lens correction, if the lens is grossly out of place
- Management of glaucoma
- Goniotomy
- Prophylactic
- Early surgical therapy - Some risk to the crystalline lens and the zonules exists because the surgery is performed from the anterior approach.
- Trabeculotomy is safer than goniotomy. The tissues can be defined more clearly, and accurate surgery can be performed. However, failures are common.
- Filtering procedures - Greater danger of injury to the crystalline lens and disturbance of the vitreous exists because the iris is absent.
- Nonperforating filtration surgery techniques are safer, because the anterior chamber remains undisturbed. Since glaucoma develops in young patients with aniridia, the intraoperative use of mitomycin is justified.
- Fugo blade can be used to produce a transconjunctival microfiltration track of 200-300 µm in any part of the angle, away from the lens and the vitreous.
- Laser therapy to angle abnormalities
- Cyclocryotherapy - Endocyclophotocoagulation in selected cases
- Glaucoma valve procedure - The choice of the techniques and the order in which they are used depends upon the peculiarities of the case and the perception of the surgeon.
Consultations
- Banded chromosome analysis on the patient and both parents
- Linkage analysis when large families are available
- Genetic counseling
Further Outpatient Care
- Lifelong, regular, and careful follow-up care is essential.
Deterrence/Prevention
- Patients should have proper genetic counseling.
- Patients should have thorough lifelong follow-up care to determine whether glaucoma is present.
Complications
- Aniridia can be complicated by the presence or association of other problems, mainly cataract and glaucoma.
Prognosis
- Prognosis varies from patient to patient.
- Unmonitored and untreated elevated intraocular pressure may damage vision.
- Cataract may require surgery.
- Progressive corneal opacification may need corneal grafting.
Patient Education
- Thoroughly educating the patient and parents about this condition and the associated ocular anomalies and systemic problems is mandatory.
Medical/Legal Pitfalls
- Failure to detect glaucoma
- Failure to educate the patient regarding all aspects of the disease, including the genetic aspects
- Failure to refer for a thorough systemic checkup
Special Concerns
- Structural iris defects: These defects may present as full-thickness holes through the iris with or without sphincter involvement. A more extensive defect with most of the iris absent is seen in aniridia.
- Other associated ocular anomalies and systemic problems are as follows:
- Wilms tumor
- Mental retardation
- WAGR (Wilms tumor, aniridia, genitourinary abnormalities, mental retardation) syndrome
| Media file 2:
Aniridia. Close-up of the superior limbus of same patient as in Media file 1, to show pannus. |
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| Media file 3:
Aniridia with a vascularized corneal opacity in a young patient. |
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| Media file 4:
Centrally placed cataractous lens and aniridia in a pediatric patient. |
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| Media file 5:
Aniridia. 3-D image showing absence of the inferior half of the iris and absence of most of the anterior leaf of the iris in the upper half. In the less affected area, the iris is represented mostly by the posterior pigment epithelium. No choroidal coloboma was present. |
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| Media file 6:
Aniridia and aphakia following perforating injury. |
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| Media file 7:
Single piece intraocular lens inside the bag, in a case of aniridia. |
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| Media file 8:
Multipiece intraocular lens inside the bag, in a case of aniridia. |
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| Media file 9:
In-the-bag intraocular lens. The lens has been displaced superiorly. |
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| Media file 10:
Aniridia. A single piece nonfoldable lens has been implanted after placing an endocapsular ring. An endocapsular ring provides better chances of centration. |
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| Media file 11:
Partial traumatic aniridia. The lost iris gap has been covered by the use of a lens optic that is clear in the center and is opaque at the periphery. A scleral fixated lens has been used in this case. |
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Aniridia excerpt Article Last Updated: Jan 17, 2008
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