Aniridia is a rare, in most cases genetically determined eye disease characterized by complete or partial absence of the iris. Clinically manifested by decreased visual acuity, horizontal nystagmus and photophobia. To diagnose the disease, it is necessary to conduct an examination of the anterior part of the eyeball, ophthalmoscopy, tonometry, gonioscopy, ultrasound biomicroscopy, and examine clinical refraction. It is possible to establish the etiology of aniridia with the help of genetic testing. Specific treatment of aniridia is based on artificial iris transplantation.
Q13.1 Lack of iris
Aniridia (irideremia) refers to a number of orphan (rare) diseases characterized by hypoplasia of the iris. The frequency of the spread of the disease is on average 1:70000. Diseases associated with aniridia include Gillespie syndrome and WAGR syndrome. Patients with irideremia are at risk of developing cataracts, glaucoma, corneal opacity. Due to the presence of a genetic mutation of the PAX6 gene, there is a high probability of pathologies of other organs and systems of the body.
Hereditary predisposition is observed in 65% of patients with aniridia, since the disease can be transmitted both by autosomal dominant and autosomal recessive type. In 35% of cases, the pathology is sporadic, caused by a mutation that first appeared. The disease is equally common among males and females, has no racial differences and features in geographical distribution.
Causes of aniridia
The etiological factor in the development of congenital aniridia is a mutation of the PAX6 gene, which is localized on chromosome 11. This gene encodes transcription factors, which at the stage of embryogenesis induce the development of the eyeball, as well as regulate the processes of differentiation of the organs of the central nervous system, nose, pancreas. In the case of pathology of PAX6 gene expression, the formation of anatomical structures of the eyeball is disrupted, which occurs at 12-14 weeks of gestation. The cause of the development of aniridia may be traumatic damage to the eyes, accompanied by the separation of the iris at the root.
The pathogenesis of this disease directly depends on the degree of functional activity of alleles of the PAX6 gene. During the differentiation of the iris, the degree of expression of protein structures of cytokeratins and adhesion factors decreases. In turn, the ability of cells to migrate from the neural crest to the place of formation of the iris stroma is lost.
With a low degree of gene expression, the differentiation of the lens and retinal pigment epithelium does not occur at the proper level, which is a prerequisite for a combination of congenital cataracts and aniridia. When the angle of the anterior chamber of the eye and the trabecular apparatus are involved in the pathological process, congenital glaucoma develops. At a more mature age, glaucoma occurs due to the formation of synechiae. Limbal stem cell deficiency also plays a role in the development of aniridia.
Symptoms of aniridia
By origin, in modern ophthalmology, congenital and acquired (traumatic) forms of aniridia are distinguished. The symptoms of traumatic irideremia depend on the degree of damage to the iris. From a clinical point of view, there are complete, partial and combined with Gillespie and WARG syndrome aniridia.
The full form of the disease is characterized by the presence of small remnants of the iris root. Clinically, the disease is manifested by a decrease in visual acuity, which is associated with underdevelopment of the structures of the eyeball. The degree of visual acuity reduction directly depends on the presence of a history of cataracts, glaucoma and keratopathy. The absence of an iris leads to increased photosensitivity. One of the symptoms of complete aniridia is horizontal nystagmus in combination with strabismus.
For partial aniridia, the same symptoms are characteristic as for the full form of pathology. But due to the fact that the disease is characterized by a mild degree of hypoplasia of the iris stroma, clinical manifestations are poorly expressed.
WARG syndrome, in addition to aniridia, includes Wilms tumor (malignant nephroblastoma), diseases of the genitourinary system and mental retardation. Often, this symptom complex includes pancreatitis and chronic renal failure. The appearance of patients may be accompanied by hemihypertrophy (hypertrophy of the muscular apparatus of one of the halves of the body). In the early stages of development, the syndrome may not have pronounced clinical manifestations, which is the reason for underdiagnosis.
Gillespie syndrome is characterized by a combination of aniridia with a clinical picture of cerebellar ataxia and mental retardation. In a number of patients, ptosis, hearing loss and pulmonary artery valve stenosis are noted.
The complex of diagnostic measures for aniridia includes visual examination of the anterior parts of the eyes, ophthalmoscopy, tonometry, gonioscopy, clinical refraction and ultrasound biomicroscopy. Genetic analysis allows to determine the cause of aniridia development. It is carried out only in the case of congenital forms of the disease.
- Eye examination. When examining the anterior parts of the eyes, it is not possible to visualize the iris. In particular cases, small clusters of the iris are observed, which is most characteristic of traumatic or partial aniridia. Ophthalmoscopy can reveal hypoplasia of the central part of the retina and optic nerve, which is characteristic of the full form of aniridia.
- Tonometry. Allows you to measure intraocular pressure. An increase in intraocular pressure above the tolerant values is a risk factor for glaucoma. Patients with aniridia are recommended to measure intraocular pressure using the iCare device, which allows manipulation without anesthetics. In order to prevent the development of glaucoma, it is necessary to carry out tonometry and ophthalmoscopy in dynamics. Gonioscopy is required in patients with elevated EDC for additional examination of the anterior chamber of the eye.
- Clinical refraction research. It is performed by skiascopy, direct ophthalmoscopy or refractometry. Depending on the concomitant pathology, emmetropic, hypermetropic and myopic refraction may be detected.
- Ultrasound biomicroscopy. The method of ultrasound biomicroscopy allows to assess the residual iris tissue and examine the fundus in patients with cataract or keratopathy.
- Genetic tests. To confirm hereditary aniridia, a FISH test and studies are performed to determine the type of defect in the PAX6 gene. The FISH test is necessary to exclude the WARG syndrome. Before the genetic analysis is carried out, it is necessary to perform ultrasound of the kidneys and pelvic organs once every 3 months.
- Other studies. Optical coherence tomography, visual evoked potentials and corneal topography are used as additional research methods.
Treatment of aniridia
The specific treatment of aniridia is based on the implantation of an artificial iris. The prosthesis consists of a special hydrogel with a hole corresponding to the pupil. The color of the artificial iris is selected according to the color of the patient’s eyes. Surgical intervention is performed with the help of transcleral surgical access.
Implantation of an artificial iris is indicated for patients with traumatic aniridia. In congenital forms of the disease, surgical intervention is performed only if the risk of corneal damage is minimal. When aniridia is combined with cataract, the tactics of the operation is reduced to the implantation of a prosthesis that replaces both the iris and the lens.
Symptomatic treatment includes the use of cosmetic contact lenses to hide the iris defect. With an increase in intraocular pressure, it is recommended to use drops from the group of carbonic anhydrase inhibitors, prostaglandins and beta-blockers. To prevent the development of keratopathy, it is necessary to use moisturizing drops and gels. All patients need to wear sunglasses that provide 100% blocking of ultraviolet rays.
Prognosis and prevention
Specific measures for the prevention of aniridia have not been developed, because the disease is associated with a genetic mutation. A family in which one of the parents has aniridia should consult a geneticist and an ophthalmologist before planning a pregnancy. Prevention of traumatic aniridia is reduced to compliance with personal safety techniques, because a strong blow can cause the iris to tear off.
If all the recommendations are followed, the prognosis for congenital aniridia is favorable for life. The development of glaucoma or the association of aniridia with Gillespie and WARG syndrome can cause early disability of the patient.