Surgical treatments for glaucoma are designed to lower intraocular pressure (IOP) by reducing resistance to aqueous humor outflow or, in the case of cyclodestructive procedures, by reducing aqueous production. Aqueous outflow can be improved by enhancing the physiologic aqueous outflow pathways or by creating alternate paths. Incisional surgery is usually undertaken when there is either documented progressive glaucomatous damage or a high risk of further damage despite maximally tolerated medical therapy. Other reasons for proceeding to surgery are situations in which medical treatment is not appropriate, not tolerated, or not properly used by a particular patient.
Incisional surgery is the first-line treatment for primary congenital glaucoma (see Chapter 11). For most other types of glaucoma, medication and/or laser surgery is tried as the initial therapy. The clinician must exercise caution when recommending incisional surgery because potential adverse effects (infections, hypotony, cataracts) can result in vision loss. Early studies of trabeculectomy as initial therapy for glaucoma, which were performed before the advent of many contemporary glaucoma medications, suggested that trabeculectomy might offer some advantages: better control of IOP, reduction in the number of patient visits to the physician, and possibly better preservation of the visual field, for example. The results of the Collaborative Initial Glaucoma Treatment Study (CIGTS; see Chapter 7) confirmed that initial surgical therapy achieves better IOP control compared with initial medical therapy; however, this did not translate to better visual field stabilization on average. In both the surgical and medication groups, there was a low incidence of visual field progression. The 9-year follow-up data suggested that initial surgery resulted in less visual field progression than did initial medical therapy in subjects with advanced visual field loss at baseline; in contrast, subjects with diabetes mellitus had more visual field loss over time if treated initially with surgery. Based on the results of this study and on current practice, most clinicians defer incisional surgery for open-angle glaucoma (OAG) unless medical and laser therapy fails. Surgical treatment can be considered earlier in patients with advanced visual field loss at presentation.
Although traditional surgeries (trabeculectomy and tube shunt surgery) are quite effective in lowering IOP, they are associated with significant risk. Thus, over the past several years, there has been a strong push to develop safer and reasonably effective alternatives. These “minimally invasive” procedures differ from traditional surgeries in that they make use of the physiologic aqueous outflow pathways. This is in contrast to trabeculectomy and tube shunt surgeries, in which a new pathway into the subconjunctival space is created.
When surgery is indicated, various factors guide the selection of the appropriate procedure. With the proliferation of minimally invasive glaucoma surgery (MIGS) devices and procedures, clinicians have a broad range of options. Each type of surgery has its own indications and contraindications; however, there is much overlap, few comparative studies are available, and the surgeon’s personal preference is often the most important factor in the selection of a procedure. Table 13-1 presents the procedures discussed in this chapter according to their location and mechanism of action.
Musch DC, Gillespie BW, Lichter PR, Niziol LM, Janz NK; CIGTS Study Investigators. Visual field progression in the Collaborative Initial Glaucoma Treatment Study: the impact of treatment and other baseline factors. Ophthalmology. 2009;116(2):200–207.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.