LASER EYE TREATMENT IRIDOTOMY
Category: Ophthalmology
Abstract :
laser eye treatment iridotomy - Diagnosis / Preparation To determine if laser iridotomy is indicated, the surgeon must first determine if and how the angle is occluded. The eye is anesthetized and the aonioscopic lens, which enables the surgeon to see the interior of the eye, is placed on the front of the eye. This is done at the slit lamp biomicroscope in a dark room. In cases of prophylactic
laser eye treatment iridotomy - Diagnosis / Preparation
To determine if laser iridotomy is indicated, the surgeon must first determine if and how the angle is occluded. The eye is anesthetized and the aonioscopic lens, which enables the surgeon to see the interior of the eye, is placed on the front of the eye. This is done at the slit lamp biomicroscope in a dark room.
In cases of prophylactic surgery, an image of the eye is taken with a ultrasound biomicroscope in both dim and bright light; this shows the doctor how the patients iris moves with dilation and constriction, and how this movement can close an angle if the patient has ocular features that predispose the eye to an angle closure.
When an angle is completely occluded (blocked), the elevated IOP usually causes corneal edema (swelling). Because this swelling can obscure the surgeons view of the iris, prior to performing a laser iridotomy, the IOP must be lowered. One technique to lower the IOP is corneal indentation, in which the gentle pressure is applied several times to the cornea with a lens or hook to open the angle. This pressure on the cornea causes a shift in the internal structures of the eye, enhances aqueous drainage, and lowers the IOP. The doctor can attempt to lower the IOP medically, as well. One drug that lowers the pressure is acetazolamide, which is given either orally or by intravenous(IV) to decrease aqueous production in the eye. This may be administered up to four times a day, until the adhesion is broken.
Another method of lowering the IOP, if acetazolamide is not effective, is with the use of hyperosmotic agents, which through osmosis causes drainage of the aqueous fluid from the eye into the rest of the body. Hyperosmotic agents are given orally; an example of such an agent is glycerine. Given by IV (intravenous administration), mannitol can be used. As the fluid drains from the eye, the vitreous - the jelly - like substance behind the lens in the posterior chamber - shrinks. As it shrinks, the lens in the eye pulls away from the vitreous, creating an opening to the anterior chamber such that aqueous fluid can flow to the anterior chamber. The success of this procedure is increased, due to gravity, if the patient is laying supine. Once the IOP has begun to decrease, the pressure is further decreased using topical glaucoma medications, such as pilocarpine, or beta blockers. Any inflammation that occurs because of the iridotomy must be controlled with steroid eye drops.
If glaucomatous-like visual field is present prior to surgical intervention, the prognosis for the patient is not as good as if the visual field were completely intact. Thus, a visual field test may be done prior to surgery.
laser eye treatment iridotomy - Aftercare
Immediately after the procedure, another drop of aproclonidine is applied to the eye. The IOP is checked every hour for a several hours postsurgery. If the IOP increases dramatically, then the increased IOP is treated until lowered. Because of inflammation is inherent in this procedure, corticosteroids are applied to the eye every five minutes for 30 minutes, then hourly for six hours. This therapy is then continued four times a day for a week. Thereafter, the patient is seen by the surgeon at one week post-surgery and again at two to six weeks post-surgery. If there are complications, the patient is seen more frequently. After the pressure has been stabilized, a visual field test to determine the extent of damage to the optic nerve may be performed again.
laser eye treatment iridotomy - Risks
The greatest risk of laser iridotomy is an increase in intraocular pressure. Usually, the IOP spike is transient and of concern to the surgeon only during the first 24 hours after surgery. However, if there is damage to the trabecular meshwork during laser surgery, the intraocular pressure may not be lowered enough and extended medical intervention or filtration surgery is required. Patients who undergo preventative laser iridotomy do not experience as great an elevation in IOP. The second greatest risk of this procedure is anterior uvetis, or inflammation within the eye. Usually the inflammation subsides within several days, but can persist for up to 30 days. Thus, the follow-up care for laser iridotomy includes the application of topical corticosteroids. A posterior synechia, in which the iris may again adhere to the lens, may occur if intraocular inflammation is not properly managed.
Other risks of this procedure include the following: swelling of, abrasions to, or opacification of the cornea; and damage to the corneal endothelium (the part of the cornea that pumps oxygen and nutrients into the iris); bleeding of the iris during surgery, which is controlled during surgery by using the iridotomy lens to increase pressure on the eye; and macular edema, which can be avoided by careful aim of the laser during surgery to avoid the macula. The macula is the part of the eye where the highest concentration of photoreceptors is found. Perforations of the retina are rare. Distortion of the pupil and rupture of the lens capsule are other possible complications.
Opacification of the anterior part of the lens is common, but this does not increase the risk of cataract formation when compared with the general population. When the iridotomy hole is large, or if the eyelid does not completely cover the opening, some patients report such side effects as glare and double vision. The argon laser produces larger holes. Patients may also complain of an intermittent horizontal line in their vision. This may occur when the eyelid is raised just enough such that a small section of the inferior part of the hole is exposed, and disappears when the eyelid is lowered. Blurred vision may occur as well, but usually disappears 30 minutes after surgery.
laser eye treatment iridotomy - Normal results
In successful laser iridotomy, the IOP differential between the anterior and posterior chambers is relieved and IOP is decreased, and the pupil is able to constrict normally. These are the results of the flatter configuration of the iris after laser iridotomy. If an angle closure is treated promptly, the patient will have minimal or no loss of vision. This procedure is successful in up to 44% of patients treated.
laser eye treatment iridotomy - Morbidity and mortality rates
For up to 64% of patients, one to three years after laser iridotomy, the IOP will rise above 21 mmHg, and long-term medical treatment is required. One-third of argon laser iridotomies will close within six to 12 weeks after surgery and will require a repeat laser iridotomy. Approximately 9% of Nd:Yag laser iridotomies must be redone for this reason. Closure of the iridotomy site is more likely if a uveitis presented after surgery. Up to 45% of patients will have anterior lens opacities after laser iridotomy, but these opacifications do not put the patient at an increased risk of cataracts.
laser eye treatment iridotomy - Alternatives
An alternative to laser iridotomy is surgical iridectomy, a procedure in which part of the iris is removed surgically. This was the procedure of choice prior to the development of laser iridotomy. The risks for iridectomy are greater than for the laser iridotomy, because it involves an incision through the sclera, the white tunic covering of the eye that surrounds the cornea. The most common complication of an iridectomy is cataract formation, occurring in more than 50% of patients who have had a surgical iridectomy. Since an incision in the eye is required for surgical iridectomy, other procedures, such as filtration surgery - if needed in the future - will be more difficult to perform. Studies comparing the visual outcomes and IOP control of laser iridotomy with surgical iridectomy show equivalent results.
In the case of acute angle closures that occur because of reasons other than, or in addition to pupillary block, argon laser peripheral iridoplasty is performed. During this procedure, several long burns of low power are placed in the periphery of the iris. The iris contracts and pulls away from the angle, opening it up and relieving the IOP
Hit: 459 times
Related Articles in Ophthalmology :
|
Add to My Bookmarks
Make My Homepage
Print
Send to a friend
Advertise with Us