Hypotony can be caused by excessive aqueous outflow (related to excessive filtration, wound leak, or cyclodialysis cleft) and/or to reduced aqueous production (due to ciliochoroidal detachment, inflammation, inadvertent use of aqueous suppressants, or extensive cyclodestruction). Transient hypotony is very common after glaucoma surgery, but it may lead to other possible complications including flat anterior chamber (Fig. 29.2), corneal edema, Descemet’s membrane folds (Fig. 29.3), choroidal effusions (Fig. 29.4), suprachoroidal hemorrhage, visual loss, cataract, macular and optic disc edema, and chorioretinal folds (predominantly in young myopic patients) [1, 2, 4].

The initial management of early postoperative hypotony with a formed anterior chamber is conservative with topical steroids and cycloplegics. Restrictions in activity (bending, weight lifting) and avoidance of Valsalva-positive conditions are recommended (Fig. 29.5). Intervention is indicated in cases when hypotony is associated with other complications such as persistent low intraocular pressure (IOP) with loss of visual acuity and hypotony maculopathy (see below). Treatment should be aimed at correcting the specific cause of hypotony. When there is a flat anterior chamber with lens–corneal touch, immediate surgical intervention is necessary to prevent endothelial damage and cataract formation. Reformation of the anterior chamber with viscoelastic can be done at the slit lamp or under the operating microscope through the paracentesis made intraoperatively. When there are large appositional choroidal effusions and the bleb is threatened, drainage of the fluid is recommended [4].

Most commonly hypotony is due to overfiltration of a filtering bleb. Several treatment options are available. Localized compression of the filtration site with a large bandage contact lens or and Simmons’ shell may be helpful [5, 6]. Several treatments have been used to induce an inflammatory or healing reaction in the filtering bleb which modifies the morphology of the filtering blebs and increase the IOP. These procedures include topical application of chemicals to the bleb surface, cryotherapy, or thermal lasers but are not very popular [7, 8]. Injection of autologous blood into the bleb can reduce overfiltration and resolve bleb leaks [9–11]. Finally, surgical revision is the most efficacious option. Resuturing the scleral flap (occasionally associated with scleral patch grafting when resuturing is not possible) is the most successful option [12–14]. Transconjunctival suturing of the sclera flap is relatively simple and effective [15, 16].

Suprachoroidal hemorrhage after surgery is rare but can be devastating. Risk factors for suprachoroidal hemorrhage include glaucoma, aphakia, previous vitrectomy, myopia and postoperative hypotony. Systemic risk factors are arteriosclerosis, high blood pressure, tachycardia, bleeding disorders, and anticoagulant therapy [30–33]. In the TVT study [20], 2 % of patients and 3 % of patients developed suprachoroidal hemorrhage after tube and trabeculectomy surgery, respectively.

Postoperative suprachoroidal hemorrhage usually occurs within the first week after glaucoma surgery and is usually associated with hypotony. The development of a suprachoroidal hemorrhage is typically acute and associated with the sudden onset of severe pain. Often this follows exertion with a Valsalva maneuver. Examination of the anterior segment frequently reveals a shallow anterior chamber (Fig. 29.10) and either a low, normal, or high intraocular pressure depending on the extent of the hemorrhage. On fundus exam a detached and dark choroid is noted. Some cases present with bleeding into the vitreous cavity. Bleeding into the vitreous cavity at the time of the hemorrhage and retinal detachment greatly worsen the visual prognosis.

Treatment of postoperative suprachoroidal hemorrhage is directed toward control of the IOP and relief of pain. The majority of these eyes will do well with this conservative management, and surgical drainage is not usually necessary. The indications for drainage through a sclerotomy include intolerable pain, a persistent flat anterior chamber, failure of bleb filtration, and massive choroidal detachments. A waiting period of at least seven to ten days following a suprachoroidal hemorrhage is advised for the fibrinolytic response to liquefy the clot and allow for more effective evacuation of the suprachoroidal space.

In general, hyphema presents at surgery or within the first two or three days following surgery (Fig. 29.11). Hyphema commonly arises from the ciliary body or cut ends of the Schlemm’s canal, though it might also arise from the corneoscleral incision or iris. The probability of having postoperative hyphema is decreased during filtration surgery bleeding by performing the internal fistula as far anterior as possible (i.e., at the cornea). In the CIGTS study bleeding into the anterior chamber was the most common intraoperative complication (8 %) and one of the most common incidents after trabeculectomy (10 %) [34]. In the TVT [20] and AGIS [35] trials the frequency of hyphema was 8 % and 11.4 %, respectively.

In the vast majority of cases, no treatment is necessary and the blood will be absorbed within a brief period of time. Cycloplegics, corticosteroids, restriction of activity, and elevation of the head of the bed 30°– 45° (to prevent blood from obstructing a superior sclerostomy) are recommended. Increased IOP can occur, particularly if the filtering site is obstructed by a blood clot, and it should be treated if necessary with aqueous suppressants. Surgical evacuation is considered depending on the level of IOP, size of hyphema, severity of optic nerve damage, likelihood of corneal blood staining, and presence of sickle trait or sickle cell anemia (infarction of the optic nerve can occur at relatively low IOP, and carbonic anhydrase inhibitors are contraindicated). Liquid blood can easily be removed with irrigation. If a clot has formed it can be removed by expression with viscoelastic or with a vitrectomy instrument set at low vacuum.

Malignant glaucoma (also called aqueous misdirection) is characterized by a shallowing or flattening of the anterior chamber without pupillary block (i.e., in presence of a patent iridectomy) or choroidal pathology (such as suprachoroidal hemorrhage), commonly with an accompanying rise in IOP. It is more common after surgery for angle-closure glaucoma, in phakic, hyperopic (small) eyes. In the TVT study [20] it occurred in 3 % of patients after tube surgery and 1 % after trabeculectomy, while its incidence in CIGTS was 0.4 % over 5 years [34].

In this condition an increased pressure at the vitreous cavity displaces the lens forward, shallowing the anterior chamber (Fig. 29.12a, b). In malignant glaucoma a relative resistance to the anterior movement of fluid from the vitreous cavity to the anterior chamber probably occurs [36].

Aqueous misdirection usually occurs in the early postoperative period. The anterior chamber is shallow and the intraocular pressure is high. However, with a functioning filtration bleb, the intraocular pressure may not be high. The peripheral iridectomy is patent, and there are no chorioretinal abnormalities.

Malignant glaucoma is initially managed with mydriatic–cycloplegic drops, aqueous suppressants, and hyperosmotic agents. If the condition is relieved (e.g., the anterior chamber has deepened), the hyperosmotic agents are discontinued first, then the aqueous suppressants are reduced or even stopped over several days. Cycloplegic drops should be continued for weeks to months.

In pseudophakic eyes a peripheral hyaloidotomy with the Nd:YAG laser may be efficient and can often be accomplished through an existing peripheral iridectomy [37]. Oftentimes, breaking the hyaloid face with the Nd:YAG laser can be done at the edge of the optic through the posterior capsule. If not successful, zonulo–hyaloido–vitrectomy via the anterior segment has been successfully used in a series of pseudophakic patients [38].

Pars plana vitrectomy should be considered when other therapies fail [39, 40]. A standard 3-port pars plana vitrectomy, removing the anterior vitreous and part of the anterior hyaloid, is done. In phakic patients, the lens can sometimes be spared, but the probability of recurrence is higher. Pars plana tube-shunt insertion with vitrectomy has been recommended to treat patients with aqueous misdirection, especially in cases with angle-closure glaucoma. The implantation of the tube shunt through pars plana can help prevent recurrence of this condition and can help in the long-term control of IOP [40].

Prevention: In high-risk eyes undergoing cataract or filtration surgery, the decompression and shallowing of the anterior chamber should be minimized. Postoperative overfiltration should be avoided with a thick scleral flap sutured tighter and with more sutures than usual. Postoperatively, judicious suture lysis or cutting/pulling releasable sutures and slow tapering of cycloplegics are recommended. A postoperative shallow anterior chamber due to overfiltration should be vigorously treated.

The phenomenon of severe visual loss after surgery, with no obvious cause, is known as “wipeout” or “snuff syndrome” (Fig. 29.13). Wipeout may affect patients who have very severe glaucomatous damage and overall is a very uncommon complication but remains an important concern among glaucoma surgeons. Wipeout was probably more common after full-thickness filtration surgery [41]. However, it is not known whether patients who had been diagnosed with wipeout could have had another undetected cause such as macular edema, hypotonous maculopathy, or inflammation. With modern surgical techniques it is becoming increasingly rare [42–44].

There are a few studies that have evaluated the incidence of wipeout after trabeculectomy. The reported incidence ranged from 0 to 0.95 % of surgeries. A retrospective study of 508 trabeculectomies identified four cases of wipeout, all of which had retrobulbar anesthesia [42]. Older patients with high preoperative IOP, advanced visual field defects affecting the central field, split fixation, and postoperative complications would appear to be at increased risk.

An inadvertent buttonhole in the conjunctiva during a filtering procedure or a wound leak, through the conjunctival incision, can be responsible for an early leaking bleb. Early leaking can flatten the bleb and lead to subconjunctival-to-episcleral fibrosis, which would jeopardize a satisfactory long-term filtration. Bleb leaks are detected with the Seidel test (Fig. 29.14). The incidence of bleb leaks in the AGIS [35], CIGTS [34], and TVT [20] studies ranged from 6 to 11 % but was much higher in both arms of the FFSS study [49] (20–32 %).

The usual cause for conjunctival buttonholes is penetration of the tissue by the tip of a sharp instrument (needle, scissors, blade) or the teeth of a forceps. Buttonholes and tears are more likely to occur in cases with extensive conjunctival scarring. To diagnose a buttonhole intraoperatively, the conjunctiva should be carefully examined at the end of the procedure by filling the anterior chamber and raising the filtering bleb. If recognized, the buttonhole should be closed at the time of surgery. If it is located in the center of the conjunctival flap, a “purse string” closure is attempted either internally on the undersurface of the conjunctiva or externally in the flap that has already been reapproximated. A 10-0 or 11-0 nylon on a tapered (“vascular”) needle should be used. When the conjunctival buttonhole or tear occurs at the limbus, it can be sutured directly to the corneal–limbal junction [4].

Early bleb leaks usually heal spontaneously, but discontinuation of topical steroids may accelerate the spontaneous closure. Prophylactic antibiotics are indicated. If there are associated complications such as shallow or flat anterior chamber, active intervention is recommended. Our preferred therapeutic modalities to treat leaking blebs include bandage contact lens, fibrin tissue glue, and surgical revision (see above) [4, 50].

Spontaneous late bleb leaks are more frequent in avascular, thin blebs, which occur more frequently when antimetabolites are used in the filtering procedure (Fig. 29.15). Leakage of the filtering bleb can be associated with hypotony, shallow–flat anterior chamber, and choroidal detachment and may increase the chances for bleb infection and subsequent endophthalmitis [4].

Bleb leaks can heal spontaneously, and conservative management with prophylactic antibiotics is recommended if there are no associated problems. Patient education regarding symptoms of bleb-related ocular infection is crucial for prompt diagnosis and management. The need and timing for surgical repair of bleb leaks depend on the presence of other complications such as severe hypotony, flat anterior chamber, vision loss, or previous episodes of bleb-related infections [51–57].