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Coexisting conditions can alter aniridia approach
For example, an aniridia ring or IOL may be necessary to create an artificial iris in a patient with coexisting cataract.
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Aniridia refers to partial or total lack of iris tissue. This generally is hereditary when it is bilateral and associated with other ocular defects. It may also occur after trauma or as an intraoperative complication.
Congenital aniridia is rare and has an incidence of one per 50,000 to 100,000 live births. About two-thirds of cases are familial whereas one-third of cases result from a new genetic mutation in the PAX6 gene, occur without a family history and have a 30% chance of developing Wilms tumor. Serial renal ultrasound is required to rule out Wilms tumor, especially in patients with no family history. Aniridia may occur as a chromosome deletion of the short arm of chromosome 11 or as sporadic.
Glaucoma
In the hereditary form of aniridia, although the iris appears absent on the slit lamp, gonioscopy shows the iris stump. The trabecular meshwork may be partially or completely covered by the iris stump, and the iris stump is generally visible. The trabecular meshwork may be normal, partly developed or abnormal. Peripheral anterior synechiae may be seen.
Glaucoma associated with aniridia may be managed medically or surgically. Surgery may involve trabeculectomy, stab incision glaucoma surgery, trabeculotomy or goniotomy. Care should be taken to avoid damage to the crystalline lens, zonules and vitreous during glaucoma surgery. Endocyclophotocoagulation and tube shunts are rarely needed. Photophobia and nystagmus may be managed with special contact lenses or IOLs. Any refractive error should be corrected, amblyopia treated and strabismus surgery performed, if indicated. Corneal pathology may require penetrating keratoplasty or Boston keratoprosthesis. However, potential complications secondary to associated limbal stem cell deficiency must be clearly kept in mind during decision-making.
Cataracts
Aniridia with coexisting cataract is managed depending on the case. Minimal cataracts and minimal subluxations may be left alone. In-the-bag IOL implantation can be decided only after taking into consideration the increased risk of progressive zonular dialysis in these patients. Aniridia rings (Figures 1 to 3) may be used for creating an artificial iris. An aniridia IOL (Figure 4) may also be used for this purpose.
Figure 1. Coloboma shields or aniridia segments have an integrated 60° to 90° tinted sector shield. The leading end is delivered into the capsular bag with McPherson forceps. The trailing end is dialed or inserted into the bag with microrhexis forceps. It is rotated so that the sector shield lies beneath the iris defect.
Figure 2. Coloboma shields protect against glare and monocular diplopia. They can be used in patients with large-sector iridectomies and traumatic iris defects. For defects greater than 90°, two such rings can be implanted with the sector shields placed adjacent to each other.
Figure 3. Aniridia with subluxated cataract. Multi-segmented aniridia ring.
Figure 4. Clinical image (a) of traumatic aniridia with aphakia. Glued iris prosthesis implanted (b). Note the 23-gauge trocar cannula used as infusion.
Images: Agarwal A
Subluxated cataracts may be removed by lensectomy, with a glued aniridia IOL placed. These IOLs have a peripheral opaque ring acting as an artificial iris. These are single-piece PMMA lenses and are larger and heavier than standard IOLs. Hence, we prefer a glued IOL technique to sclerally fixate these IOLs in a stable manner. A larger corneoscleral tunnel is required. Haptic exteriorization must be done with care because the PMMA haptic may break. A larger sclerotomy is required.
Another option in cataractous lenses is to retain the anterior and posterior capsules and place the aniridia glued IOL over the capsule. This gives additional support to the heavier IOL while also maintaining the vitreous face. In children, a posterior curvilinear capsulorrhexis may be performed to avoid visual axis opacification.
Visual impairment
The degree of visual impairment is not correlated with the degree of aniridia and is generally because of other associated ocular conditions such as cataract, corneal changes, glaucoma, optic nerve hypoplasia and foveal hypoplasia, all of which lead to decreased vision, nystagmus, strabismus and amblyopia. Uncontrolled glaucoma can also cause visual loss over time. Photophobia and decreased visual acuity are common symptoms. Limbal stem cell deficiency, pannus, microcornea and ulcers may be seen. Fifty percent to eighty-five percent of patients develop lens opacities in the first two decades. Phacodonesis, ectopia lentis and complete lens dislocation may occur.
Acquired aniridia
Aniridia may also occur after trauma. This is generally associated with extensive ocular injury, as in a case of pseudophacocele with total traumatic aniridia. Any associated vitreous pathology may require the assistance of a vitreoretinal surgeon. Iatrogenic aniridia may occur during phaco, especially if there is already coexisting iridodialysis or a floppy iris. These cases are often complex and have other associated morbidity. In case of complete iris avulsion, an aniridia glued IOL may be used.
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Amar Agarwal, MS, FRCS, FRCOphth, is director of Dr. Agarwal’s Eye Hospital and Eye Research Centre. Agarwal is the author of several books published by SLACK Incorporated, publisher of Ocular Surgery News, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at 19 Cathedral Road, Chennai 600 086, India; email: dragarwal@vsnl.com; website: www.dragarwal.com.Disclosure: No products or companies that would require financial disclosure are mentioned in this article.