Fig. 36-40  Argon laser bleb treatment. With the patient under topical anesthesia, foci of bleb leakage (or the margins of large blebs, as illustrated here) can be lightly coagulated with an argon laser, using a large spot size and minimal energy. Topical dyes, such as fluorescein or rose bengal, may enhance the thermal absorption.

(From Lieberman MF: Complications of glaucoma surgery. In: Charlton J, Weinstein G, editors: Ophthalmic surgery complications, Philadelphia, Lippincott-Raven, 1995.)

Argon laser energy can be delivered to the surface of a conjunctival bleb that has been stained by swabbing it with methylthioninium chloride dye (Fig. 36-40). Laser settings of 400–700 mW with a 500- m spot size applied for 0.2–0.5 second will shrink the surface of the bleb. Because bleb perforation has occurred with this technique, it should be used with caution in blebs pretreated with antimetabolites, which may fail to heal spontaneously.

Dellen

If a bleb is markedly elevated at the limbus, the lid cannot spread tears over the adjacent cornea, and dellen form (Fig. 36-41).188 These dellen are almost always self-limited and may be palliated with ointment, frequent tear replacement eyedrop application, or nonsteroidal anti-inflammatory drops. Steroid drops may be contraindi­ cated because they retard corneal surface healing; vascularization of the base in fact precedes healing.189 Cryotherapy over the bleb adjacent to the dellen has been effective.

Hypotonous maculopathy

One complication of hypotony may occur early or late, within hours or days, after the reduction of IOP. Although reported many decades ago during the advent of full-thickness filtering procedures,190 hypotonous maculopathy was later described

reported in filters augmented both with 5-FU192,193 and mito- mycin-C.194–196 It is characterized by persistent hypotony (usually

Fig. 36-41  Dellen adjacent to a bleb. A large bleb after filtering surgery prevents the tear film from reaching that area of the cornea. Spontaneous healing is the rule.

defined as IOP less than 5 mmHg) for many weeks after surgery, with decreased visual acuity.197 Funduscopic examination and OCT imaging 198 reveal no specific macular edema but rather choroidal wrinkling behind the macula leading to the appearance of choroidal folds – particularly well seen on redfree photography. Subsequent series have identified two risk factors

associated with hypotonous maculopathy and loss of vision: high myopia and age younger than 50.199,200 These factors most likely

relate to decreased scleral rigidity in the area of the posterior pole

and tendency towards collapse in the presence of low IOP. Low pressure alone is not incompatible with good visual acuity.199,201

Although it has been established that there is a slight decrease in the axial length of the eye after glaucoma shunt procedures or

trabeculectomy without the use of antimetabolite (on the order of 0.27 mm),202,203 eyes with hypotonous visual loss often require

vigorous intervention to reduce the apparent effect of a collapsed posterior pole.

By and large, non-surgical interventions (e.g., soft contact lenses,

bleb size reduction by cryotherapy,195 autologous blood injections (Fig. 36-42), with or without compression sutures,204–206 argon

laser to the bleb207) are inconsistently effective. Returning to the operating room for tightly resuturing the scleral flap and elevat-

ing the IOP for the short term offers the most expeditious return of visual function and retention of IOP control,200,208–210 although

a less complicated procedure has been described.210b Occasionally more extensive surgery, such as vitrectomy with intraocular gas, is required.211 Avoidance of hypotony altogether with the primary surgery is, of course, the optimal procedure; surgical technique modifications with this goal in mind have been described.212

When IOPs are consistently brought above the level of 6 mmHg, a return of visual function is seen in most eyes. It sometimes takes 8–24 months until restoration to within 1 or 2 Snellen lines of the preoperative acuity is achieved, albeit with some persistent metamorphopsia. Return of vision is faster with higher post-repair IOPs.

Late hypotony after filtering surgery

Hypotony resulting from overfunctioning or perforation of a thinwalled filtering bleb has been described in an earlier section. Less frequently, delayed hypotony is encountered with ciliochoroidal

Fig. 36-42  Autologous blood injection. After a sterile extraction of approximately 1 ml of the patient’s blood, a small 27-gauge needle is applied to the same syringe, and with the patient under topical anesthetic the autologous blood is injected into the bleb itself. Because of the high likelihood of blood entering the anterior chamber, this technique is sometimes varied to first fill the anterior chamber with sodium hyaluronate (Healon), which may produce a tamponade effect that minimizes the extent of the iatrogenic hyphema.

(From Lieberman MF: Complications of glaucoma surgery. In: Charlton J, Weinstein G, editors: Ophthalmic surgery complications, Philadelphia, Lippincott-Raven, 1995.)

detachment and no apparent filtering bleb. This occurs as a result of multiple separate mechanisms.23,213

presence of hypotony, gonioscopy may be difficult because of corneal folds; intracameral viscoelastic can be injected through a

paracentesis at the slit lamp to permit visualization and, if needed, argon laser can be applied to the cleft.215,216 Visualization of such

clefts is also possible with UBM imaging.217 Sometimes the clefts are invisible or ‘migratory,’ appearing in different locations on different occasions as though the ciliary ring is fish-mouthing in different areas.218

When not visualized, clefts can be surmised from the eye’s response to atropine (elevation of pressure) or miotics (hypotony). Their occult location is often associated with the most recent surgical site, such as a filtration site, a recent phacoemulsification wound,219 posterior lens suture site,220 or limbal incision made during an anterior chamber lens implant removal.222

The first line of therapy is full cycloplegia with atropine, with the possibility of an acute rise in IOP that may require prompt medical intervention. Multiple argon or diode223 laser applications to the cleft, cryotherapy, and trans-scleral suturing221 through the cleft have all been successful treatments.

Hypotony with aqueous suppression therapy in contralateral eye

Timolol in the fellow eye and oral acetazolamide therapy after previous failed trabeculectomy have been reported to cause profound hypotony with ciliochoroidal detachment in the operated eye.224 The postulated mechanism implies supersensitivity of the ciliary epithelium to the pharmacologic agent, which causes profound aqueous suppression. We have also seen one case resulting from topical epinephrine therapy. The hypotony usually disappears with cessation of the drug. Such supersensitivity may also appear as a crossover effect when the fellow eye is being treated with a -blocker; the recently filtered eye may respond with hypotony but IOP may rise when drops are discontinued in the other eye.

Hypotony with occult filtering ‘bleb’

In rare cases after filtering or cataract surgery there may be an efficiently functioning limbal filtering site that cannot be recognized by routine clinical examination. There is no apparent evidence of a filtering bleb by either slit-lamp examination or gonioscopy. If other causes of hypotony cannot be found, injection of fluorescein into the anterior chamber can demonstrate whether such a filter exists by detection of accumulated fluorescein in a focal area of the perilimbal subconjunctival space. Such sites may be closed by one or two applications of cryotherapy sufficient to produce a 1–2-mm ice ring around the area of the fistula. If this fails, surgical exposure and direct suturing of the fistula with a trans-scleral absorbable suture almost always closes it. The pressure, however, may temporarily rise and respond only to miotics.

Hypotony with occult cyclodialysis clefts

A similar situation occurs with undetected cyclodialysis clefts, the size of which is unrelated to the extent of hypotony.214 In the

Hypotony from retinal detachment

The sudden onset of hypotony in any eye should cause suspicion and examination of the eye for a retinal detachment.225 This is especially true after vitrectomy for eyes at risk for rhegmatogenous lesions (e.g., vitreoretinal proliferation in diabetes). If a detachment is found, retinal repair will resolve the hypotony.

Hypotony from iritis or ischemia

Late hypotony resulting from iritis may occur after filtering surgery. Chronic uveitis and prior surgeries may also predispose to cyclitic membranes, which contract and detach the underlying ciliary body, with subsequent hypotony.226 Visualization of such membranes can be done with scleral depression and indirect ophthalmoscopy or by ultrasonic imaging; if found, surgical repair is necessary. A rare cause of chronic hypotony with inflammation is ischemia from vasculitis.227 If no other cause for the hypotony is evident in the presence of chronic flare and cell, treatment with topical cycloplegics and corticosteroids frequently will resolve the problem.18