Glaucoma is a group of diseases with patients who present with varying degrees of optic nerve damage and visual field loss as well as individually varied general medical, ophthalmic, and social issues. All of these factors combine to make the risk/benefit ratio and the decision to do glaucoma surgery different for each patient. Incisional glaucoma surgery, whether by filtering surgery, aqueous tube shunt, or nonpenetrating procedures, lowers intraocular pressure (IOP) by providing an alternative path for aqueous humor outflow and often stops or limits progression of the disease. The decision to perform incisional glaucoma surgery is based upon knowledge of the natural history of glaucoma progression correlated with a particular patient’s history and status, the patient’s response to medical and laser therapy, the benefits of surgery, and contraindications to and risks of surgery.

Patients with advanced glaucoma who have not reached a targeted low IOP are appropriately managed surgically in order to reach the clinically indicated low target IOP. Incisional glaucoma surgery is typically recommended only when medical and laser therapies have failed to prevent optic nerve damage or visual field loss or lower IOP to a level that will prevent such loss. Initial glaucoma surgery without prior medical or laser therapy is rarely appropriate or performed in the USA but may be for a patient presenting with advanced glaucoma damage and high IOP for whom urgent IOP control is the best hope to salvage vision. Most patients are tried on multiple topical antiglaucomatous medications, often in combination, including a prostaglandin analog, a beta-adrenergic blocker, an alpha agonist, and a topical carbonic anhydrase inhibitor. Pilocarpine, phospholine iodide, and oral carbonic anhydrase inhibitors may be tried, but their side effects frequently preclude long-term use. All the topical antiglaucomatous medications may cause side effects that limit their use: allergic reactions, precipitation of asthma, keratitis, and decreased vision, for example. Some patients may experience annoying side effects such as increased skin pigmentation, hyperemia, and ocular irritation. Should these patients have glaucoma surgery to relieve their symptoms? That question can be answered only after an extensive discussion of the possible benefits and complications of surgery. The complex medication schedule and the cost of chronic medical therapy may prevent a patient’s persistence with an otherwise successful medication plan. If these barriers to chronic successful management of glaucoma cannot be overcome, glaucoma surgery may be necessary to provide long-term control of the disease.

Many patients requiring glaucoma surgery are concomitantly receiving anticoagulation therapy for other comorbidities, including arrhythmia, cardiac prosthetic valve, or thromboembolic disease resulting from various etiologies. The alternative of complete discontinuation of anticoagulation therapy before surgical intervention has raised concerns about the risk of serious thromboembolic events in the perioperative period in these patients. Glaucoma surgeons are usually concerned about hemorrhagic complications of anticoagulation that can ultimately affect surgical success.

Anticoagulation therapy is commonly categorized in two groups: those undergoing therapy with warfarin and those undergoing therapy with an antiplatelet agent (clopidogrel and aspirin [acetylsalicylic acid]). The common intraoperative and postoperative surgical complications associated with blood thinning medications include retrobulbar hemorrhage, hyphema, vitreous hemorrhage, and suprachoroidal hemorrhage.

A few retrospective studies have analyzed hemorrhagic complications of glaucoma surgery in patients using anticoagulation therapy.1,2 Law and colleagues reported a higher incidence of complications following glaucoma surgery in patients who were on either warfarin or antiplatelet therapy compared to controls, with the highest rate of complication noted in patients who continued warfarin therapy through surgery. In this study, there were less hemorrhagic complications in patients who discontinued coumadin compared with those who continued anticoagulation; however, the difference failed to reach statistical significance. Similarly, in a retrospective examination of 367 trabeculectomies, Cobb et al. observed that continuation of either warfarin or aspirin therapy in those undergoing surgery had approximately twice the risk of hyphema. However, the use of aspirin did not adversely affect the eventual surgical outcomes, whereas warfarin’s use ultimately resulted in poor surgical outcomes and intraocular pressure (IOP) control.

Alwitry and colleagues reported that most glaucoma surgeons in the UK do not routinely stop anticoagulation therapy prior to glaucoma surgery. A smaller percentage of these surgeons chose to discontinue long-term anticoagulation therapy and initiate heparin therapy. Bleeding complications secondary to anticoagulation therapy are not limited to the glaucoma surgical patient, as there have been concerns among surgeons in other subspecialties including vitreoretinal surgery and oculoplastic surgery. However, a unique aspect of glaucoma surgery is the risk of hypotony and hypotony-related complications, including suprachoroidal hemorrhage, during the early postoperative period. In high-risk eyes, glaucoma surgeons may choose to discontinue anticoagulation during the perioperative period or use other techniques to reduce the risks of hemorrhagic complications during and after surgery.

When surgeons choose to discontinue anticoagulant therapy, the approaches vary and can be individualized to each patient. In patients treated with warfarin, the drug can be discontinued for a minimum of 3 days prior to surgery to improve coagulation intraoperatively and postoperatively. The patient’s primary care practitioner may allow withholding warfarin for an additional several days after surgery, which may avoid postoperative complications in high-risk eyes. It is worth noting that warfarin cessation may lead to a rise in clotting factors that put the patient in a hypercoagulable state, shown to peak at one week afterwards [5, 8]. Because aspirin has a prolonged anti-platelet aggregation effect, some surgeons recommend cessation of aspirin therapy one or two weeks prior to surgery, with approval by the patient’s primary care provider. Discontinuation of aspirin on the day of surgery probably has little or no influence on the antiplatelet effect of the drug during the perioperative and immediate post-operative period.

There are risks associated with discontinuation of long-term anticoagulation therapy in patients undergoing surgery. The risk of thromboembolic events is probably low (less than 1 %). However, some of these problems such as pulmonary embolus or stroke can be life-threatening. In each patient, the ocular risk of continuation of anticoagulant therapy should be weighed against the systemic risk of life-threatening hemorrhagic complications. Communication and coordination with the physician who is managing the long-term anticoagulant therapy is strongly recommended, along with a frank discussion with the patient of the risks and benefits of altering anticoagulation therapy in the perioperative period.

Alternatives to discontinuation of anticoagulation therapy may be tried in order to reduce the risk of bleeding complications. Modifying anesthetic methods may be helpful, including use of topical and local anesthesia in order to minimize the risk of retrobulbar hemorrhage associated with retrobulbar injection of anesthetic. Surgical techniques, also, may be modified to avoid hemorrhagic complications. Meticulous use of hemostasis during flap dissection, anterior placement of sclerotomy to avoid the ciliary body, and omitting surgical iridectomy have been shown to avoid bleeding. Tightly securing the scleral flap to prevent bleeding and postoperative hypotony has been advocated. Postoperative hypotony increases the risk of bleeding complications, specifically suprachoroidal hemorrhage. In glaucoma drainage implant surgery, use of suture ligatures around the tube or two-stage surgery can reduce the rate of postoperative hypotony. Intraoperative and postoperative use of viscoelastics may avoid or mitigate problems associated with hypotony. Gradual reduction of the IOP during surgery may avoid dramatic fluctuations in IOP, which increase the risk of bleeding complications.

In summary, the current literature suggests that patients receiving anticoagulation therapy with warfarin and/or antiplatelet agents who are candidates for glaucoma surgery are at increased risk for serious hemorrhagic complications. Many glaucoma subspecialists continue anticoagulation through surgery, although surgeons may modify their anesthetic and surgical techniques to minimize complications. In patients at high risk for ocular hemorrhagic complications, the surgeon may recommend withholding anticoagulant therapy during the perioperative period. In all instances, ophthalmologists should collaborate with the patient’s physician and other medical specialists in assessing the patient’s risk of hemorrhagic ocular complications, the systemic risk of discontinuing anticoagulant therapy, and the perioperative plan for use of anticoagulant drugs.

Surgeons become comfortable with either limbal- or fornix-based flaps and it becomes their “fastball.” That being said, it is useful to note the advantages and disadvantages of both incisions for trabeculectomy.