SURGERY FOR INFANTILE AND JUVENILE GLAUCOMA
Perhaps the most satisfactory operations for treatment of primary congenital (infantile) glaucoma are goniotomy and trabeculotomy ab externo (see Ch. 19 ). Goniotomy is safe when performed under gonioscopic visualization by a trained surgeon, and usually can be performed without scarring the eye in ways that interfere with later procedures. Successful surgery improves aqueous outflow, probably by restoring outflow through Schlemm’s canal, and can be maintained for long periods or even indefinitely. However, recurrences of increased pressure in some of the children originally operated on 40 or more years ago make lifelong surveillance of these patients a necessity.
The patient’s family should be informed that an examination under anesthesia (EUA) will be undertaken to determine the extent of glaucoma and the patient’s ocular health; all of the attendant risks of general anesthesia should be mentioned. If control of the glaucoma is uncertain, it is in the operating room at the conclusion of the EUA that decisions are made regarding whether to operate, which type of surgery to undertake, and whether to proceed on one or both eyes. All risks and benefits should be explained, and the long-term nature of the cooperative effort between doctor and family should be emphasized. All equipment for the EUA should be readily available, including gonioscopy lenses, microscopes, light sources, calipers, tonometers, pachymeter, ophthalmoscopes, and imaging devices such as a B-scan or fundus camera. A-scan measurements of axial length may be helpful in following progression or lack thereof in the first 2–3 years of life.
If the intraocular pressure (IOP) is elevated and the cornea is hazy, preoperative medical therapy may clear the cornea and facilitate goniotomy. Many classes of effective topical medications, such as β-blockers, prostaglandins, and carbonic anhydrase inhibitors (topical or oral), may be given cautiously. The physician and family should remain alert to side effects of medications in children (see Ch. 22 ). Infants and children receiving topical β-blockers should be monitored for apneic spells or bronchospasm; the use of α-agonists in children under 6 years is contraindicated . To alleviate the risk of potential cardiopulmonary problems, the anesthesiologist should be made aware of any preoperative medications used by the patient.
If surgery is being considered, the pupil should not be preoperatively dilated for examination of the optic nerves because this increases the risk of lens injury during either goniotomy or trabeculotomy. Often the discs can be satisfactorily viewed with a direct ophthalmoscope through a Koeppe lens used at the time of gonioscopy; or ophthalmoscopy through a dilated pupil (e.g., for photographs) can be postponed until future examination. Often, a quite satisfactory view of the optic nerve can be obtained with the use of one drop of topical tropicamide 1%. If the pupil is not constricted at the conclusion of the EUA, miotic intracameral preparations (carbachol or acetylcholine) can be administered at the time of surgery.
If necessary for visualization of the angle, goniotomy can be preceded by application of topical anhydrous glycerin or removal of the cloudy corneal epithelium. The safety of goniotomy depends on good visibility, and epithelial haze may increase after the diagnostic and surgical contact lenses have been used. If a great deal of edema is present, a sheet of epithelium comes off easily. Otherwise, considerable pressure on a curet or the side of a ♯15 Bard-Parker blade may be needed to remove the epithelial layer. Scrubbing the cornea with an applicator soaked in 70% ethyl alcohol loosens the epithelium and makes its removal much easier, but may increase postoperative discomfort.
If corneal edema is severe, only the junction point of the iris to the trabecular meshwork may be visible; this may be adequate for placement of the goniotomy incision. If extreme haziness is present, trabeculotomy is recommended.
Attention to detail is of utmost importance in goniotomy. A variety of classical surgical techniques are described here.
Two locking Elschnig forceps are used by the assistant to grasp the superior and inferior rectus muscles while the surgeon holds the lid out of the way with a muscle hook and turns the eye with forceps to expose the site of each tendon insertion. A speculum is not needed and would be in the way of the forceps throughout the procedure.
The patient’s head is turned 30–45° away from the surgeon to prevent air bubbles from accumulating under the modified Hoskins-Barkan or Swan surgical contact lens ( Fig. 37-1 ). The surgeon’s left forefinger or an angled toothed forceps holds the contact lens against the eye. The Elschnig forceps under the surgeon’s left hand must be rotated out of the way by the assistant. A drop of balanced salt solution (BSS) is placed under the contact lens. The lens is rotated away from the near limbus so that there will be ample room for the goniotomy knife to enter the cornea.
A high-powered binocular operating room microscope, as is used in phacoemulsification procedures, works well for this procedure; foot control for ‘X-Y-Z’ manipulation of the viewing system is extremely helpful. Tilting the head of the microscope to facilitate the view of the chamber angle may also be helpful. A paracentesis should first be made for the introduction of a miotic if needed and for inserting a viscoelastic to maintain and protect the anterior chamber. Entry of the knife into the anterior chamber should be done under low magnification. Higher power is used for the trabecular incision.
The assistant holds the eye so that the plane of the iris is parallel to the direction of the knife thrust. The eye should be lifted upward from the orbit to permit maximum exposure and should be rotated so that the incision can sweep for 4 or 5 clock hours of angle, allowing a second goniotomy to be performed on the opposite side if needed (see Fig. 19-22 ).
The contact lens is held against the cornea, several millimeters away from the lateral limbus ( Fig. 37-2 ), to allow the goniotomy knife to enter the cornea 1–2 mm inside the limbus. The assistant needs to hold the eye against the pressure of the knife as it enters the cornea obliquely to minimize aqueous loss during and after the procedure. Care should be taken to penetrate the cornea neither too tangentially nor too perpendicularly. A Swan goniotomy knife ( Fig. 37-3 ) with a thin, straight shaft helps maintain the chamber when the instrument is withdrawn. The blade is double sided so that the goniotomy incision can be made in opposite directions without rotating the knife. The blade is passed across and to the far side of the anterior chamber with a slight back-and-forth rotating motion around the long axis of the knife to facilitate its passage through the cornea.
The knife tip should engage the trabecular meshwork just below Schwalbe’s line and barely enter the meshwork ( Figs 37-4 and 37-5 ). Then with the use of the corneal entry site as the fulcrum, the surgeon can make a 100–110° incision in the meshwork in stages, pausing each 40–50° while the assistant rotates the eye to allow a new area of the meshwork to be incised. There should be no feeling of resistance in the tissue. If the blade is too deep and is cutting sclera, a grating sensation occurs (like cutting a lettuce core). If a cut of more than 50& is attempted in one direction, it may be difficult to maintain the chamber depth and keep the cornea free of folds and thereby more difficult to maintain accurate visual control of the knife tip. Visual control is essential to prevent misplacement of the incision. If the knife goes into the anterior ciliary body, severe and possibly disastrous bleeding may occur. If the knife strikes the lens, a cataract will form. If the incision extends anterior to Schwalbe’s line, it is useless therapeutically. If it goes into the sclera, bleeding and fibrous proliferation are likely. The knife should be removed smoothly and quickly, with its handle kept parallel to the iris to avoid contact with the lens.
If an experienced assistant is not available, a modified goniotomy technique may be easier. A pediatric lid speculum (Wiener or Barraquer) is used. 4-0 silk sutures placed beneath the tendons of the superior and inferior rectus muscles will satisfactorily position the globe. The sutures are then clamped to the drapes to provide fixation of the globe. The Swan-Jacob goniolens ( Fig. 37-6 ), which provides excellent angle visualization, requires no saline instillation under the lens. As with the previously described technique, the operating microscope is used for visualization of the angle throughout the operation. With the patient’s head turned slightly away from the surgeon, the goniolens is applied to the cornea, and the microscope is adjusted to bring the angle into sharp focus. The lens is then removed from the cornea and held above the eye by the nurse so that it may be readily grasped by the surgeon and placed on the cornea.
Viscoelastic should be introduced to maintain a constant anterior chamber depth. The goniotomy can be performed with a needle-knife or 25–27-gauge needle attached to a hollow cannula. The cannula is connected to a syringe by means of plastic tubing and filled with BSS. The eye is grasped at the limbus with a toothed forceps, and the needle-knife (with the bevel down) is forced through the cornea just inside the limbus. It is then directed across the anterior chamber until the tip can be seen approaching the angle. If the chamber shallows, additional viscoelastic can be injected. Once the area of the angle is approached, the surgeon sets the toothed forceps aside, grasps the goniolens, and places it on the cornea, bringing the angle into focus. Viscoelastic injection is useful not only for maintaining the chamber depth but also for stretching the iris–trabecular meshwork attachment for easier and more bloodless surgery. The goniotomy incision is then performed as discussed previously. The chamber is deepened slightly, and the needle-knife is slowly withdrawn.
A third alternative is to use the Worst goniotomy lens, which is sutured to the limbus. Facing the surgeon, there is a hole in the flange of the lens through which the goniotomy knife enters the eye.The lens is used to stabilize the eye. This technique is also useful if no experienced assistant is available. Another approach, with limited validation in the literature, may be to use the Trabectome™ to perform trabecular ablation (see Ch. 38 ).
If ocular pressure and normal chamber depth can be maintained, bleeding is minimized. If necessary, BSS is instilled with a flat needle ( Fig. 37-7 ) to irrigate blood from the anterior chamber and to deepen the chamber at the close of the procedure. Viscoelastic can be left in the eye; the surgeon may wish to use an aqueous suppressant for the first 12–24 hours postoperatively. After withdrawal of the goniotomy knife, the corneal wound may tend to leak. Either a 10-0 nylon suture closure or small-cannula injection of BSS into the corneal stroma at the edges of the entry site can be performed to seal the wound. An antibiotic ointment is instilled, and an aluminum shield is taped over the operated eye.
If no viscoelastic was used, the patient’s head should be kept turned as much as possible toward the side of the puncture wound for the first hour after surgery to keep the goniotomy incision upward so that blood can flow away from it. Within 3 days, any blood present has usually disappeared from the anterior chamber.
The child should be seen routinely in the first few weeks after surgery to ascertain the absence of infection, the corneal health, and chamber depth; if possible, IOP measurement can be attempted (see Ch. 19 ). A follow-up EUA should be scheduled 4–6 weeks after the goniotomy, with preparations for additional surgery if the IOP is elevated or if the cornea and disc show deterioration. If symptoms and signs have not improved or are worsening, re-examination and reoperation may be performed after 3 weeks. Repeat surgery sooner than this may not allow enough time for the eye to stabilize and the first procedure to be effective. In one study, a higher preoperative IOP elevation was more predictive of surgical failure than if two simultaneous goniotomies were performed at the initial operation.
If IOP is controlled, the child is re-examined in 2 months, then every 3–4 months for a year, twice in the next year, and annually thereafter. Intensive amblyopic management is essential to maximize visual potential.
If the pressure is still not normalized, or the disc cupping has failed to reverse in the first 4–6 weeks postoperatively, the technically more difficult temporal goniotomy, with the knife passed over the bridge of the nose, can be performed as the second operation. If two goniotomies fail, the third operation should be a trabeculotomy, which can be done temporally or superiorly. Large series of such cases were reported by Mandal and co-workers in India to respond well to combined trabeculotomy/trabeculectomy, or trabeculectomy with antimetabolite.
Complications of goniotomy include those of general anesthesia in a neonate or infant, bleeding from the site of goniotomy, infection, failure, and epithelial ingrowth. In cases of bilateral uncontrolled infantile glaucoma, the small risk of two general anesthesias within a few days of one another may nevertheless be greater than the small risk of performing bilateral goniotomies at one sitting. This possibility should be addressed with the parents in instances of bilateral disease. At the conclusion of the first procedure, completely fresh operative supplies – new IV bottles (ideally from separate manufacturing lots), gowns and gloves, sterile drapes and instruments, repeat sterile wash-ups by surgeons and nurses, etc. – should be used to eliminate the remote risk of bilateral intraocular infection: a risk thought to be less than the persistence of uncontrolled glaucoma and its possible unavoidable delay for quick surgical redress.
The two essentials in performing skillful and safe goniotomies are thorough knowledge of the gonioscopic appearance of the infant angle and adequate practice of the technique under gonioscopic control. This is not a procedure that should be performed only occasionally. A good gonioscopist can quickly acquire knowledge of the infant angle by performing gonioscopy on babies who are under anesthesia for some other purpose, such as strabismus surgery. The surgical skill can be obtained by practice on animal eyes fastened (by toweling and thumbtacks) to a wooden block; the angle appearance of the cat eye is comparable to that of the human infant eye ( Fig. 37-8 ).