Angle Surgery
Brenda L. Bohnsack, MD, PhD
PREOPERATIVE CONSIDERATIONS
Angle surgery is highly effective in many forms of glaucoma that affect children, often providing long-term and in many cases lifetime IOP control. However, the success of angle surgery is dependent on the type of childhood glaucoma and the angle configuration (see Chapter 9).
Primary congenital glaucoma (PCG): Angle surgery is the mainstay of PCG (70%-90% success rate) and should be the first surgical approach in these cases.1,2,3,4,5,6,7
Juvenile open angle glaucoma (JOAG): Angle surgery has been shown to effectively control IOP in 50%-70% of cases of JOAG.8,9,10,11,12 Similar to PCG, angle surgery should be considered as a first surgical approach in JOAG.
Glaucoma following cataract surgery (GFCS): In GFCS, if the angle is open, then angle surgery should be the first surgical approach and can be effective in obtaining IOP control.8,11,13 However, if the angle is closed, then angle surgery is less likely to be successful and there is the risk of disinsertion of the iris root at the time of surgery.
Uveitic glaucoma: Uveitic glaucoma is often mixed-mechanism, and the angle configuration preoperatively is important to assess. In eyes with an open-angle and good preoperative inflammation control, angle surgery is successful in 60%-80% of cases.14,15,16,17
Sturge-Weber glaucoma: Glaucoma in Sturge-Weber syndrome can be due to goniodysgenesis and/or increased episcleral venous pressure. In eyes with goniodysgenesis as evidenced by an open angle with immature trabecular meshwork and dysplastic iris insertion, angle surgery may be effective in controlling IOP.18,19,20 However, the presence of a choroidal hemangioma in these eyes should be evaluated preoperatively given the increased risk of suprachoroidal hemorrhage due to hypotony.21,22 An ab externo approach has increased the risk of hypotony; thus, an ab interno approach may be the safer option in eyes with choroidal hemangiomas.
SURGICAL APPROACHES
Angle surgeries are categorized by the surgical approach (ab externo, ab interno) and the amount of angle treated. The 180-degree trabeculotomy and 180-degree
goniotomy have been the traditional angle surgeries employed for over 70 years.23,24,25,26,27 However, in the last 25 years, many studies have shown that 360-degree trabeculotomy (ab externo or ab interno) may yield higher success rates and longer IOP control.8,9,11,28,29,30,31 Nonetheless, in eyes with congenital anomalies or previous surgeries, the suture or catheter may not be able to be passed 360 degrees and a 180-degree approach may be required.
goniotomy have been the traditional angle surgeries employed for over 70 years.23,24,25,26,27 However, in the last 25 years, many studies have shown that 360-degree trabeculotomy (ab externo or ab interno) may yield higher success rates and longer IOP control.8,9,11,28,29,30,31 Nonetheless, in eyes with congenital anomalies or previous surgeries, the suture or catheter may not be able to be passed 360 degrees and a 180-degree approach may be required.
Ab Externo Approach
Advantages: Does not require gonioscopic view; may be combined with trabeculectomy.
Disadvantages: Requires conjunctival incision; longer operating time compared to ab interno approach.
Ab Interno Approach
Advantages: Preservation of conjunctiva; shorter operating time compared to ab externo approach.
Disadvantages: Requires clear cornea for gonioscopic view.
SURGICAL PROCEDURES
Ab Externo Approach
Place partial-thickness 7-0 Vicryl traction sutures at the superior and inferior limbus. Rotate the eye superonasally to expose the inferotemporal quadrant (Figs. 10.1A).
Create a 3-clock hour conjunctival peritomy inferotemporally with Westcott scissors. Bluntly and sharply dissect off Tenon capsule. Use Wet-Field cautery for hemostasis (Figs. 10.1A and B, 10.2A and B).
Using a combination of a 7515 blade and mini-crescent blade, create a 3-mm triangular scleral flap with 75% depth that extends beyond the limbus just into the clear cornea (Figs. 10.1C and 10.2C).
Reflect the scleral flap over the cornea and identify the approximate location of Schlemm canal, which is “where blue and white meet” just posterior to the limbus. NOTE: Especially in buphthalmic or microphthalmic eyes, Schlemm canal may be shifted more posteriorly or anteriorly than the anticipated location due to stretching of the sclera or abnormalities in development of the cornea, scleral, and angle structures.
Carefully dissect in the anticipated location of Schlemm canal with a 7515 blade. The main landmark is the circumferential scleral fibers, which are the bed of Schlemm canal. Look for an egress of aqueous humor to identify the canal (Figs. 10.1D and 10.2D).
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