IRIDECTOMY LASER IRIDOTOMY
Category: Ophthalmology
Abstract : Description Laser iridotomy / iridectomy 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 rep
Description
Laser iridotomy / iridectomy
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.
Conventional (surgical) iridectomy
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.
Diagnosis / Preparation
Closed-angle glaucoma
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 closedangle glaucoma, he or she will feel intense pain, and is likely to be seen on an emergency basis with the following symptoms:
• nausea and vomiting
• severe pain in or above the eye
• visual disturbances that include seeing halos around lights and hazy or foggy vision
• headache
• redness and watering in the affected eye
• a dilated pupil that does not close normally in bright light
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
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.
Preparation for treatment
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.
Aftercare
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.
Risks
The risks of a laser iridotomy or iridectomy include the following:
• irritation in the eye for two to three days after the procedure
• bleeding
• scarring
• failure to relieve fluid pressure in the eye
The risks of a conventional iridectomy include:
• infection
• bleeding
• scarring in the area of the incision
• failure to relieve fluid pressure
• formation of a cataract
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
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.
Morbidity and mortality rates
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
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.
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