An iridectomy is a procedure in eye surgery in which the surgeon removes a small, full-thickness piece of the iris, which is the colored circular membrane behind the cornea of the eye. An iridectomy is also known as a corectomy. In recent years, lasers have also been used to perform iridectomies.
Today, an iridectomy is most often performed to treat closed-angle glaucoma or melanoma of the iris. An iridectomy performed to treat glaucoma is sometimes called a peripheral iridectomy, because it removes a portion of the periphery or root of the iris.
In some cases, an iridectomy is performed prior to cataract surgery in order to make it easier to remove the lens of the eye. This procedure is referred to as a preparatory iridectomy.
Closed-angle glaucoma is a condition in which fluid pressure builds up inside the eye because the fluid, or aqueous humor, that is produced in the anterior chamber at the front of the eye cannot leave the chamber through the usual opening. This opening lies at the angle where the iris meets the cornea, which is the clear front portion of the exterior cover of the eye. In closed-angle glaucoma, the fluid is blocked because a part of the iris has moved forward and closed off the angle. As a result, fluid pressure in the eye rises rapidly, which can damage the optic nerve and lead to blindness. About 10% of all cases of glaucoma reported in the United States is closed-angle. This type of glaucoma is also called angle-closure glaucoma, acute congestive glaucoma, narrow-angle glaucoma, and pupillary block glaucoma. It usually develops in only one eye at a time.
There are two major types of closed-angle glaucoma: primary and secondary. Primary closed-angle glaucoma most commonly results from pupillary block, in which the iris closes off the angle when the pupil of the eye becomes dilated. In some cases, the blockage happens only occasionally, as when the pupil dilates in dim light, in situations of high stress or anxiety, or in response to the drops instilled by a doctor during an eye examination. This condition is referred to as intermittent, subacute, or chronic open-angle glaucoma. In other cases, the blockage is abrupt and complete, leading to an attack of acute closed-angle glaucoma. In primary glaucoma, the difference between the chronic or intermittent forms and an acute attack is usually due to small variations in the anatomical structure of the eye. These include an unusually shallow anterior chamber; a lens that is thicker than average and situated further forward in the eye; or a cornea that is smaller in diameter than average. Any of these differences can narrow the angle between
Secondary closed-angle glaucoma results from changes in the angle caused by disorders, medications, trauma, or surgery, rather than by the anatomy of the eye itself. In some cases, the iris is pulled up into the angle by scar tissue resulting from the abnormal formation of blood vessels in diabetes. Another common cause of secondary closed-angle glaucoma is uveitis, or inflammation of the uvea, which is the covering of the eye that includes the iris. Cases have been reported in which uveitis related to HIV infection has led to closed-angle glaucoma. Melanoma of the iris has also been associated with closed-angle glaucoma.
Any medication that causes the pupil of the eye to dilate may cause an acute attack of closed-angle glaucoma, including antihistamines and over-the-counter cold preparations. Medications that are given to treat anxiety and depression, particularly the tricyclic antidepressants and the selective serotonin reuptake inhibitors (SSRIs), may trigger the onset of closed-angle glaucoma in some patients. In other instances, anesthesia for procedures on other parts of the body produces an acute attack.
In terms of trauma, a direct blow to the eye can dislocate the lens, bringing it forward and blocking the angle; overly vigorous exercise may have the same effect. Lastly, certain types of eye surgery performed to treat other conditions may result in secondary closed-angle glaucoma. These procedures include implantation of an intraocular lens; cataract surgery; scleral buckling to treat retinal detachment; and injection of silicone oil to replace the vitreous body in front of the retina following a vitrectomy.
Melanoma of the iris is a malignant tumor that develops within the pigmented cells of the iris; it is not a cancer that has developed elsewhere in the body and then spread to the eye. Melanoma of the iris can, however, enlarge and gradually destroy the patient's vision. If left untreated, it can also metastasize or spread to other organs—most commonly the liver—and eventually cause death.
Closed-angle glaucoma affects between 350,000 and 400,000 people in the United States; in some Asian countries such as China, however, it is more common than open-angle glaucoma.
Risk factors for closed-angle glaucoma include:
Melanoma of the iris is a relatively rare form of cancer, representing only about 10% of cases of intraocular melanoma. The American Cancer Society estimates that about 220 cases of melanoma of the iris are diagnosed in the United States each year. People over 50 are the most likely to develop this form of cancer, although it can occur at any age. It appears to affect men and women equally. Melanoma of the iris is more common in Caucasians and in people with light-colored irides than in people of Asian or African descent. Suspected causes include genetic mutations and exposure to sunlight.
A person who is at risk for an acute episode of closed-angle glaucoma or who has already had emergency medical treatment for an attack may be treated with a laser iridotomy to reduce the level of fluid pressure in the affected eye. The drawback of a laser iridotomy in treating closed-angle glaucoma is that the hole may not remain open, requiring repeated iridotomies, a laser iridectomy, or a surgical iridectomy. In addition, laser iridotomies have a higher rate of success when used preventively rather than after the patient has already had an acute attack.
To perform a laser iridotomy, the ophthalmologist uses a laser, usually an argon or an Nd:YAG laser, to burn a small hole into the iris to relieve fluid pressure behind the iris. If the procedure is an iridectomy, the laser is used to remove a full-thickness section of the iris. The patient sits in a special chair with his or her chin resting on a frame or support to prevent the head from moving. The ophthalmologist numbs the eye with anesthetic eye drops. After the anesthetic has taken effect, the doctor shines the laser beam into the affected eye. The entire procedure takes between 10–30 minutes.
Melanoma of the iris is usually treated by surgical iridectomy to prevent the tumor from causing secondary closed-angle glaucoma and from spreading to other parts of the body.
A surgical iridectomy is a more invasive procedure that requires an operating room . The patient lies on an operating table with a piece of sterile cloth placed around the eye. The procedure is usually done under general anesthesia. The surgeon uses a microscope and special miniature instruments to make an incision in the cornea and remove a section of the iris, usually at the 12 o'clock position. The incision in the cornea is self-sealing.
Closed-angle glaucoma may be diagnosed in the course of a routine eye examination or during emergency treatment for symptoms of an acute attack. A doctor who is performing a standard eye examination may notice that the patient's eye has a shallow anterior chamber or a narrow angle between the iris and the cornea. He or she may perform one or both of the following tests to evaluate the patient's risk of developing closed-angle glaucoma. One test, called tonometry, measures the amount of fluid pressure in the eye. It is a painless procedure that involves blowing a puff of pressurized air toward the patient's eye as the patient sits near a lamp and measuring the changes in the light reflections on the patient's corneas. Other methods of tonometry involve the application of a local anesthetic to the outside of the eye and touching the cornea briefly with an instrument that measures the fluid pressure directly. The second test, gonioscopy, involves the use of a special mirrored contact lens to evaluate the anatomy of the angle between the iris and the cornea. The doctor numbs the outside of the eye with a local anesthetic and touches the outside of the cornea with the gonioscopic lens. He or she can use a slit lamp to magnify what appears on the lens. Patients with subacute, intermittent, or chronic closed-angle glaucoma can then be treated before they develop acute symptoms.
If the patient is having a sudden attack of closed-angle glaucoma, he or she will feel intense pain, and is likely to be seen on an emergency basis with the following symptoms:
These symptoms are produced by the sharp rise in intraocular pressure (IOP) that occurs when the angle is completely blocked. This increase can occur in a matter of hours and cause permanent loss of vision in as little as two to five days. An acute attack of closed-angle glaucoma is a medical emergency requiring immediate treatment . Emergency treatment includes application of eye drops to reduce the pressure in the eye quickly, other eye drops to shrink the size of the pupil, and acetazolamide or a similar medication to stop the production of aqueous humor. In severe cases, the patient may be given drugs intravenously to lower the intraocular pressure. After the pressure has been relieved with medications, the eye will require surgical treatment.
Melanoma of the iris is usually discovered in the course of a routine eye examination because it will be visible to the ophthalmologist as he or she looks through the pupil in the center of the iris. A melanoma on the iris may look like a dark spot or ring, or it may resemble tapioca. The doctor can perform a gonioscopy, and use specialized imaging studies to rule out other possible eye disorders. An ultrasound study can be made by using a small probe placed on the eye that directs sound waves in the direction of the tumor. Another test is called fluorescein angiography , which involves injecting a fluorescent dye into a vein in the patient's arm. As the dye circulates throughout the body, it is carried to the blood vessels in the back of the eye. These blood vessels can be photographed through the pupil.
In a minority of patients, melanoma of the iris is discovered because the patient is experiencing eye pain resulting from a rise in IOP caused by tumor growth.
Patients scheduled for a laser iridotomy or iridectomy are not required to fast or make other special preparations before the procedure. They may, however, be given a sedative to help them relax. Patients scheduled for a conventional iridectomy are asked to avoid eating or drinking for about eight hours before the procedure.
Short-term aftercare following laser iridectomy or iridotomy is minimal. Patients are asked to make arrangements for someone to drive them home after surgery, but can usually go to work the next day and resume other activities with no restrictions. They should not need any medication stronger than aspirin for discomfort.
Short-term aftercare following a surgical iridectomy includes wearing a patch over the affected eye for several days and using eye drops to minimize the risk of infection. The surgeon may also prescribe medication for discomfort. It will take about six weeks for vision to return to normal. Long-term aftercare following an iridectomy for closed-angle glaucoma usually involves taking medications to help control the fluid pressure in the eye and seeing the ophthalmologist for periodic checkups.
Aftercare for melanoma of the iris includes eye checkups to be certain that the tumor has not recurred. In addition, patients are advised to reduce their exposure to sunlight and other sources of ultraviolet light.
The risks of a laser iridotomy or iridectomy include the following:
The risks of a conventional iridectomy include:
The risks of an iridectomy for melanoma of the iris include glaucoma resulting from the formation of new blood vessels near the angle, cataract formation, and recurrence of the tumor. In the event of a recurrence, the standard treatment is enucleation, or surgical removal of the entire eye.
Normal results for a laser-assisted or conventional iridectomy are long-term lowering of IOP and/or complete removal of a melanoma on the iris.
About 60% of patients who have had conventional iridectomies consider the operation a success; 15%, on the other hand, maintain that their vision was better before the procedure.
Fortunately for patients, melanoma of the iris is a relatively slow-growing form of cancer; it metastasizes to the liver in only 2–4% of cases. If treated promptly, it has a high survival rate of 95–97% after five years.
Alternatives to a conventional iridectomy for the treatment of closed-angle glaucoma include repeated laser iridotomies or the long-term use of such medications as pilocarpine. Another surgical alternative, which is most commonly done when the size of the lens is a factor in pupillary block, is removal of the lens.
Alternatives to iridectomy in the treatment of melanoma of the iris include watchful waiting, periodic eye examinations, and the use of medication to control any symptoms of closed-angle glaucoma.
See also Laser iridotomy .
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Rebecca Frey, PhD
Iridectomies are performed by ophthalmologists, who are physicians who have completed four to five years of specialized training in the medical and surgical treatment of eye disorders. Ophthalmology is one of 24 specialties recognized by the American Board of Medical Specialties.
Laser iridotomies or iridectomies are done as an outpatient procedure, either in the ophthalmologist's office or in an ambulatory surgery center. Surgical iridectomy is done in an operating room, either in a surgery center that specializes in ophthalmology or in a specialized eye hospital.