A goniotomy is a surgical procedure primarily used to treat congenital glaucoma, first described in 1938. It is caused by a developmental arrest of some of the structures within the anterior (front) segment of the eye. These structures include the iris and the ciliary body, which produces the aqueous fluid needed to maintain the integrity of the eye. These structures do not develop normally in the eyes of patients with isolated congenital glaucoma. Instead, they overlap and block the trabecular meshwork, which is the primary drainage system for the aqueous fluid. As a result of this blockage, the trabecular meshwork itself becomes thicker and the drainage holes within the meshwork are narrowed. These changes lead to an excess of fluid in the eye, which can cause pressure that can damage the internal structures of the eye and cause glaucoma.
All types of congenital glaucoma are caused by a decrease in or even a complete obstruction of the outflow of intraocular fluid. The ocular syndromes and anomalies that predispose a child to congenital glaucoma include the following: Reiger's anomaly; Peter's anomaly; Axenfeld's syndrome; and Axenfeld-Rieger's syndrome. Systemic disorders that affect the eyes in ways that may lead to glaucoma include Marfan's syndrome; rubella (German measles); and the phacomatoses, which include neurofibromatosis and Sturge-Weber syndrome. Since these disorders affect the entire body as well as the eyes, the child's pediatrician or family doctor will help to diagnose and treat these diseases.
The purpose of a goniotomy is to clear the obstruction to aqueous outflow from the eye, which in turn lowers the intraocular pressure (IOP). Lowering the IOP helps to stabilize the enlargement of the cornea and the distension and stretching of the eye that often occur in congenital glaucoma. The size of the eye, however, will not return to normal. Most importantly, once the aqueous outflow improves, damage to the optic nerve is halted or reversed. The patient's visual acuity may improve after surgery.
Goniotomies are commonly performed to treat the following eye disorders:
- Congenital glaucomas.
- Aniridia. Aniridia is a condition in which the patient lacks a visible iris. A goniotomy is performed as a preventive measure, as 50%–75% of patients with aniridia will develop glaucoma.
- Uveitic glaucoma associated with juvenile rheumatoid arthritis.
- Maternal rubella syndrome.
The congenital glaucomas affect 1: 10,000 infants, with boys affected twice as often as girls. Both eyes are affected in 75% of patients. These glaucomas are differentiated from the secondary glaucomas caused by such medical conditions as juvenile rheumatoid arthritis (JRA), Marfan's syndrome, or diabetes; or caused by intraocular tumors, cataract surgery, or trauma. Many of the secondary glaucomas respond better to medical treatment than to surgical treatment. Ninety-five percent of developmental or congenital glaucoma appears before age three. Another type of pediatric glaucoma is usually diagnosed between ages 10 and 35 and resembles the type of glaucoma seen in adults more closely than the congenital glaucomas, although some developmental anomalies may be present. This type of glaucoma is referred to as juvenile-onset open angle glaucoma (JOAG).
Congenital glaucoma is a polygenic disorder; that is, it involves more than one gene. Since this type of glaucoma is inherited and the genes for JOAG and congenital glaucoma have been mapped, genetic testing is available to determine whether a specific child is at risk for these disorders.
Before the surgeon begins the procedure, the patient is given miotics, which are drugs that cause the pupil to contract. This partial closure improves the surgeon's view of and access to the trabecular meshwork; it also protects the lens of the eye from trauma during surgery. Other drugs are administered to lower the intraocular pressure.
Once the necessary drugs have been given and the patient is anesthetized, the surgeon uses a forceps or sutures to stabilize the eye in the correct position. The patient's head is rotated away from the surgeon so that the interior structures of the eye are more easily seen. Next, with either a knife-needle or a goniotomy knife, the surgeon punctures the cornea while looking at the interior of the eye through a microscope or a loupe. An assistant uses a syringe to introduce fluid into the eye's anterior chamber through a viscoelastic tube as the surgeon performs the goniotomy.
A gonioscopy lens is then placed on the eye. As the eye is rotated by an assistant, the surgeon sweeps the knife blade or needle through 90–120 degrees of arc in the eye, making incisions in the anterior trabecular meshwork, avoiding the posterior part of the trabecular meshwork in order to decrease the risk of damage to the iris and lens.
Once the knife and tubing are removed, saline solution is introduced through the hole to maintain the integrity of the eye and the hole is closed with sutures. The surgeon then applies antibiotics and corticosteroids to the eye to prevent infection and reduce inflammation. The head is then rotated away from the incision site so that blood cannot accumulate. The second eye may be operated on at the same time. If the procedure needs to be repeated, another area of the eye is treated.
The clinical signs of congenital and infantile glaucoma may be detected within a few months after birth. They include an enlarged eye, called buphthalmos; corneal swelling; decreased vision; tearing; sensitivity to light; and blepharospasm, or uncontrolled twitching of the eyes. These signs, however, are usually absent in JOAG. As a result, glaucoma in the older child may go undetected until the child loses vision.
The examiner must take some measurements in order to confirm a diagnosis of glaucoma, including measurement of the corneal diameter and the axial length of the eye. The corneal diameter is usually less then 10 mm in an infant and only 11–12 mm in a one-year-old, but can be as large as 14 mm in a child with advanced glaucoma. The axial length is measured with an A-scan, which is a type of ultrasound. The doctor will also determine the intraocular pressure with either Schiotz tonometry or a TonoPen. An elevated intraocular pressure is not always present in congenital glaucoma; unless it is extremely high, it is only one factor in the diagnosis of glaucoma. Gonioscopy, a technique used to examine the interior structures of the eye, is performed by placing a special contact lens on the eye. This lens, used in combination with a biomicroscope, allows the surgeon to evaluate the structures of the anterior part of the eye. The condition of the optic nerve is also evaluated; photos or drawings may be taken for future comparison.
Since cooperation is difficult for infants and young children, these assessments may be done either under anesthesia or with the use of a sedative. Older children are examined in a manner similar to adults.
Once the diagnosis of glaucoma is confirmed, goniotomy is often the first line of treatment. If goniotomy is determined to be the best procedure and there is a lot of corneal haze, the surgeon may treat the patient for several days pre-operatively with azetozolamide to lower the IOP and increase the clarity of the cornea. Or, he may elect to perform another procedure called a trabeculotomy, which is the preferred surgery if the corneal diameter is greater than 14 mm. The patient is given antibiotics for several days before surgery.
Obtaining the family's informed consent is another important part of preparing for a goniotomy. The surgeon tells the family that the child will need general anesthesia, and that several postoperative visits with anesthesia or sedation will be necessary after the goniotomy.
The patient will continue to be given antibiotics, corticosteroids, and miotics for one to two weeks after surgery. If the surgeon believes that the procedure was not successful, then he or she may give the patient acetazolamide by mouth in addition to these medications for up to 10 days to lower the IOP.
The patient will be anesthetized again three to six weeks after surgery for a reevaluation of the anterior chamber of the eye. This examination is repeated every three months for the first year; every six months during the second year; and once a year thereafter. Once the child is older, usually three to four years old, the physician can perform the follow-up examination in his or her office without anesthesia or sedation. Since a visual field test is difficult or impossible to do on an infant or young child, the doctor measures the cornea to assess progression of the disease. An increase in corneal diameter indicates that the glaucoma is getting worse. Visual field testing will be performed when the child is old enough to understand it. A visual field test can establish the extent of vision loss that has occurred because of glaucoma.
An important aspect of managing glaucoma patients after surgery is assessing the degree of nearsightness and astigmatism, both of which result from the stretching of the eye caused by increased intraocular pressure. If the child needs eyeglasses, they should be given as early in life as possible to decrease the probability of amblyopia. Amblyopia is a condition in which the vision cannot be corrected completely, even with glasses, and is common for pediatric glaucoma patients. Although almost 80% of children with congenital glaucoma can have their vision corrected to 20/50 or better, patching of an eye and vision therapy is often required to achieve this level of correction.
About 10% of goniotomy patients will experience a recurrence of the glaucoma or have it develop in the unaffected eye. As a result, the patient will need periodic eye examinations for the rest of his/her life. If glaucoma does recur later in life, then either medical or surgical treatment is instituted depending on the cause.
Since goniotomy is performed under general anesthesia, there is some risk of a reaction to the anesthetic. The most common risk of general anesthesia in infants is cardiorespiratory arrest. This complication is not life-threatening, however, and occurs in fewer than 2% of goniotomies.
A hyphema (bleeding and formation of a blood clot in the anterior chamber) is the most common complication of a goniotomy. In most cases, however, the blood clots resolve within a few days.
If the cornea is not clear during surgery, the surgeon may accidentally sever the iris from the ciliary body or separate the ciliary body from the sclera of the eye. Both of these complications can lead to hypotony, a condition in which the integrity of the eye is compromised because of insufficient intraocular fluid.
Other complications of goniotomy are cataract formation; inflammation in the anterior chamber; scarring of the cornea; subluxation or dislocation of the lens; and retinal detachment. The risk of damage to the lens is greater when the patient is aniridic.
The intraocular pressure may increase in spite of, or due to complications of the procedure, and the goniotomy may have to be repeated. If the goniotomy is not successful after two or three attempts, the surgeon will perform a trabeculotomy.
Goniotomy is considered to be successful when the measured IOP is below 21 mm/Hg, or below 16 mm/Hg if the patient is under anesthesia; when there is no increase in corneal diameter; and when damage to the optic nerve is stabilized or even reversed. Goniotomy is successful in about 94% of patients with primary congenital glaucoma in decreasing IOP, corneal haze, and corneal diameter. Tearing, sensitivity to light, and blepharospasm all decrease over time.
If a goniotomy is successful it will be apparent within three to six weeks. A repeat goniotomy is required for 50% of patients. Goniotomy is most successful when the child is between one month and three years of age; it is successful only a quarter of the time in patients younger than one month. It is also more successful when the corneal diameter is less than 14 mm and when the IOP is not extremely high. Even if the IOP has been lowered, anti-glaucoma medication or drops may still be needed after the goniotomy.
When a goniotomy is performed on patients with uveitic glaucoma, the success rate is 75%–83%, although most of these patients need ongoing medication for glaucoma, and 30% require a repeat procedure.
Morbidity and mortality rates
Fifteen years after a goniotomy, one in seven patients will have such serious complications as corneal decompensation or detachment of the retina. Vision loss occurs in 50% of children with congenital glaucoma in spite of surgical and medical intervention. This is particularly true of infants diagnosed with glaucoma before two months of age. About 50% of children who undergo goniotomy require a repeat procedure. Complications are more common for patients treated as young infants and as older children.
Congenital glaucoma does not respond well to medical treatment, so the first line of treatment is usually surgical. Medical therapy is often initiated as adjunct therapy after surgery.
One alternative to goniotomy is trabeculotomy. Goniotomy has been the preferred procedure for treatment of congenital glaucoma, but trabeculotomy has been favored in recent years because of the surgeon's difficulty in seeing the structures in the eye when the cornea is hazy. A clear view of the cornea is required for goniotomy. In a trabeculotomy, the surgeon inserts a probe into the eye, passes it through Schlemm's canal, and rotates it inside the anterior chamber in order to tear a hole in the trabecular meshwork. This maneuver creates an alternative passageway for the aqueous fluid to leave the anterior chamber of the eye. In some cases the surgeon will perform a trabeculectomy , a procedure in which part of the trabecular meshwork is removed by cutting, at the same time as the trabeculotomy.
Another alternative procedure involves placement of a filtering shunt to direct the intraocular fluid out of the eye. A shunt is often placed if Schlemm's canal cannot easily be located, as in the case with infants. The safety profile for trabeculotomy and filtering surgery are comparable to goniotomy, but there is a higher rate of long-term success with goniotomies and trabeculotomies.
A newer variation of surgical goniotomy is laser goniotomy, in which the surgeon uses a Yag:Nd laser to cut into the trabecular meshwork. Laser goniotomies appear to be less effective than surgical goniotomies, but if a patient responds well to a laser procedure, then surgical goniotomy may be considered.
Other alternative treatments for pediatric glaucoma are the cyclodestructive techniques, which include cyclophotocoagulation, and the more commonly performed cyclocryotherapy . These procedures involve destruction of the ciliary body by using either freezing temperatures or lasers. These procedures have lower success rates and a higher risk of complications; they are usually performed as a last resort when other techniques have failed.
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Martha Reilly, OD
WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?
A goniotomy is performed in a hospital by an ophthalmologist, or eye specialist, while the patient is under general anesthesia. Preoperative and postoperative evaluations are also done in a hospital setting if anesthesia is required. These evaluations can be done for older children in an office setting. An ophthalmologist qualified to perform a goniotomy has usually had advanced fellowship training in glaucoma surgery after completing a 3-year residency in ophthalmology.
QUESTIONS TO ASK THE DOCTOR
- How many goniotomies have you performed?
- Have you had advanced training in glaucoma surgery?
- What are the chances that the procedure will need to be repeated?
- Is a goniotomy the best surgical procedure for my child?