Ординатура / Офтальмология / Английские материалы / Glaucoma Surgery_Trope_2005

1.INTRODUCTION: TERMINOLOGY

In 1869, von Graefe (1) described a rare complication that followed peripheral iridectomy (PI) for acute angle closure glaucoma. The condition was characterized by shallowing of the anterior chamber (AC) together with high intraocular pressure (IOP), and usually resulted in blindness. von Graefe used the term “malignant” glaucoma because it did not respond to conventional therapy and its propensity to progress to blindness. Consequently, the term malignant glaucoma expresses its seriousness and not a neoplastic disease.

Other terms have also been used to describe this condition. Weiss and Shaffer (2) suggested the term ciliary block glaucoma based on the theory that obstruction to normal aqueous flow was due to apposition of the ciliary processes against the lens equator or anterior hyaloid.

The term aqueous misdirection (3) implies that aqueous humor is diverted posteriorly due to ciliary block.

The term direct lens block angle closure (4) was suggested to describe the fact that a forward shift of the lens results in this syndrome.

All these terms reflect the pathogenesis of the condition unlike the prognostic term malignant glaucoma which is still widely used by ophthalmologists. Because of the fact that there is no agreement regarding the pathogenesis, we use the term malignant glaucoma in this chapter although we feel it should be dropped as soon as the pathogenesis has been clearly elucidated. We also strongly advise ophthalmologists to use this term with caution in front of patients. They may misinterpretate this name and think they have a form of eye cancer.

2.DEFINITION: CLINICAL DIAGNOSIS

Classically, malignant glaucoma presents clinically with the following characteristics:

1.Axial shallowing or flattening of the AC (both centrally and peripherally).

2.Increased IOP, which initially may start low or normal. Generally, the IOP is higher than expected in an eye with a flat AC from overfiltration or bleb leakage, that is, .4 6 mmHg; however, the IOP usually progressively rises.

3.Patent PI excluding pupillary block.

4.Absence of clinically visible posterior segment abnormalities on ophthalmoscopy or B-scan ultrasound.

5.Ultrasound biomicroscopic (UBM) evidence of a low supraciliary effusion (5,6).

The typical presentation occurs in a phakic patient following filtration surgery for uncontrolled angle closure glaucoma developing in 2 4% of the operated eyes (7). The onset of this condition may occur from the first postoperative day to many months or years later.

Malignant glaucoma has been reported in association with intracapsular (8) and extracapsular cataract surgery with anterior or posterior chamber intraocular lens (IOL) implantation (8,9), aphakia (10,11), and with or without an associated filtering procedure (12). More recently, it has been reported in a patient with a phakic posterior chamber IOL for myopia correction (13), following deep sclerectomy (14), glaucoma drainage device (Baerveldt valve) implantation (15), retinal detachment surgery with buckling (16), and pars plana vitrectomy (PPV) (17). Malignant glaucoma may also develop after needling of a trabeculectomy bleb (18).

level (5,6), also imaged by UBM, is likely responsible for the forward movement of the ciliary body and the ciliolenticular block.

In addition, the anterior hyaloid may contribute to the ciliolenticular block and to the posterior pooling of the aqueous, by two possible mechanisms:

1.In 1978, Shaffer (45) postulated that breaks in the anterior hyaloid near the vitreous base allow for the posterior diversion of aqueous into the vitreous. He suggested that the vitreous breaks prevent forward aqueous flow, acting as oneway valves. However, the existence of such a mechanism has not been proven.

2.Epstein et al. (46) provided evidence that there may be resistance to aqueous permeability through the vitreous body. It has been postulated that this resistance is increased by the elevation of ocular pressure (39,46,47). Additional experimental confirmation of the earlier data was provided by Fatt (47) who measured the hydraulic flow conductivity of animal vitreous in vitro and noted that as pressure increases in the vitreous it becomes dehydrated and fluid conductivity decreases. In addition, the forward displacement of the vitreous against the anterior structures (ciliary body, lens, and iris) (due to the posterior-to-anterior pressure difference) leads to a decrease of the available anterior diffusional area through which fluid flows (41,46,48). This increases the vitreous resistance to forward fluid flow and malignant glaucoma is more likely to happen (40,46).

3.2.Slackness or Laxity of the Lens Zonules

Chandler and Grant (39) suggested that weak or slack zonular fibers, as well as pressure from the vitreous allow partial subluxation of the lens iris diaphragm. The laxity of the zonules may be the result of pseudoexfoliation (5), prolonged angle closure (49) or ciliary muscle spasm induced by miotics, surgery, trauma, inflammation, or unknown factors (4). Supraciliary effusion with anterior rotation of the ciliary processes aids this process (5,6,14,42 44).

3.3.Positive Pressure Phenomenon

Quigley et al. (40) recently proposed a mechanism for malignant glaucoma development, attributable to the following factors: (1) positive pressure phenomenon (due to choroidal expansion) and (2) poor vitreous fluid conductivity.

Patients at higher risk to develop this condition are older persons with a high prevalence of posterior vitreous detachment. Choroidal expansion increases the pressure behind the vitreous gel. This partially compressed vitreous (in the predisposed eye) is likely to have higher than normal resistance to fluid flow. When the usual anterior-to-posterior transvitreal flow is insufficient to equalize the pressure differential between the vitreous cavity and the posterior chamber and AC, the compressed vitreous further decreases its water conductivity. The compressed vitreous then moves forward, carrying the iris lens diaphragm with it.

Increases in choroidal volume can move the lens forward. In the average human eye, the choroidal volume is 480 mL and the AC volume is 150 mL. Consequently, if the choroid expands by 20%, it would occupy 100 mL of space, equal to 2/3 of the AC volume. This forward movement is more dramatic if there is reduced pressure from an incision in the AC, leading to malignant glaucoma. It is important to note that choroidal volume expansion has not been validated to date as an etiological factor in malignant glaucoma.

ostium (5), despite the presence of a patent iridectomy, resulting in a rise in IOP. The aqueous is directed posteriorly rather than anteriorly and the amount of the misdirected aqueous is increased as a vicious cycle develops. The vitreous is pressurized by fluid transfer across the anterior hyaloid face; its fluid conductivity is decreased reducing uveoscleral outflow through the choroid leading to increased pressure from aqueous accumulation in the vitreous cavity providing additional forward momentum to the lens position.

In conclusion, although some basic information about malignant glaucoma awaits confirmation, it seems likely that most aspects of the described mechanisms contribute in variable degrees to the development of this form of glaucoma. Future research is required to fully verify the role of choroidal expansion, water flow from the vitreous and the relevance of supraciliary effusions. UBM will be an important tool as it is the only method available at this time that consistently detects small effusions.

4.DIFFERENTIAL DIAGNOSIS

Early detection and appropriate intervention are critical to the successful management of malignant glaucoma. It is also important to remember that the accurate diagnosis of this form of glaucoma is a clinical one and requires the exclusion of the following important entities.

Table 22.1 Differential Diagnosis of Malignant Glaucoma

4.1.Suprachoroidal Hemorrhage

The eye with a suprachoroidal hemorrhage typically has an acute onset of severe ocular pain, associated with a flat AC and markedly elevated IOP. Suprachoroidal hemorrhage can occur during surgery or in the postoperative period, following ocular surgical procedures. The eye is usually quite inflammed.

Ophthalmoscopy reveals the presence of single or multiple dark reddish-brown choroidal elevations that are frequently similar in size to those in serous choroidal detachment but can be seen in the posterior pole to the vortex veins.

The use of ultrasound examination (A- and B-scan) is helpful in the following clinical circumstances:

1.If the posterior pole cannot be visualized on ophthalmoscopy, due to corneal or medial opacities;

2.to provide echographic clues in order to differentiate suprachoroidal hemorrhage from serous choroidal detachment;

3.to follow the course of the suprachoroidal hemorrhage and determine whether intervention should take place and when.

The B-scan echographic findings in suprachoroidal hemorrhage reveal the presence of large dome-shaped elevations that extend to the posterior pole, inserting next to rather than into the optic disc. On B-scan, detection of spontaneous motion from the blood vessels on the surface of the hemorrhagic choroidal detachments is occasionally helpful to establish the diagnosis of suprachoroidal hemorrhage, especially in the presence of appositional (kissing) configuration (51). Typically, reflective echoes are noted in the suprachoroidal space on both B- and A-scan due to the presence of hemorrhage (52). Early echographic finding indicates a large, solid clot in the suprachoroidal space surrounded by fluid blood. As the clot becomes older it also becomes less reflective on A-scan and less dense on B-scan (53). Echography may be useful to follow the course of the clot appearance and size and to determine the optimal time for drainage.

Small suprachoroidal hemorrhages usually spontaneously absorb. Larger hemorrhages are drained after the clot lysis at about 2 weeks (see Chapter 21 in this book for further management of this condition).

4.2.Pupillary Block

Pupillary block glaucoma should be ruled out because it can mimic malignant glaucoma as a shallow AC with elevated IOP. Nevertheless, there are two very important clinical features that help to make an accurate diagnosis.

Following filtration surgery, malignant glaucoma presents with axial shallowing of the AC as the entire iris lens diaphragm is shifted forward with high normal or raised IOP. On the other hand, in pupillary block glaucoma the IOP is usually high, the pupil is middilated, the central AC is formed and the peripheral iris is typically bowed forward (iris bombe´).

Attention should also be directed to the presence of a patent iridectomy. The presence of a patent iridectomy is of significant diagnostic value because it will relieve pupillary block, although it has no effect in malignant glaucoma. Consequently, if an iridectomy is present and clearly patent then the diagnosis of pupillary block is ruled out. If there is no iridectomy present or if there is any doubt about the patency of the existing iridectomy, then another one should be created (Table 22.1).

It is important to remember that malignant glaucoma is characterized by a normal posterior segment anatomy on ophthalmoscopy and B-scan ultrasound examination and that the UBM finding consistent with the diagnosis of malignant glaucoma is the presence of a small amount of annular supraciliary fluid (5,6) that is not clinically observable.

5.MANAGEMENT

Malignant glaucoma is a serious complication of intraocular surgery. Prevention, early detection, and timely intervention are critical for optimal results and successful management.

5.1.Risk Factors: Prevention

The major risk factors for the development of malignant glaucoma include uncontrolled angle closure glaucoma (5), preoperative shallow AC, hyperopia, nanophthalmos and short axial length, pseudoexfoliation (5), partial or total closure of the AC during the time of surgery (10), and the presence of malignant glaucoma in the fellow eye (4). Sudden decompression of the eye as a result of suture lysis or corneal perforation is an important cause of malignant glaucoma (5,7). Furthermore, discontinuation of cycloplegics and aqueous suppressants, in an eye with controlled malignant glaucoma, is associated with recurrence of this form of glaucoma (5). Finally, there is evidence that plateau iris configuration is a risk factor for the development of malignant glaucoma (42).

Preoperative measures include discontinuation of miotics and use of aqueous suppressants and hyperosmotics to lower the IOP before the eye is surgically opened.

Intraoperative maneuvers include paracentesis of the AC, so as to slowly decompress the eye with uncontrolled IOP, as well as the use of preplaced sutures to facilitate the rapid closure of the incision and minimize surgically induced hypotony. A PI should always be performed. Tight flap sutures prevent overfiltration. At the end of the operation, the AC should be reformed with air or viscoelastic to ensure that the chamber maintains its depth.

Postoperatively, cycloplegic therapy should start in the operating room and continue for weeks or months. Corticosteroids should always be used to minimize uveal tract inflammation. In addition, close monitoring of the AC depth and cautious laser suture lysis are also critical to successful management of malignant glaucoma.

It is important to be aware of the eyes at particular risk of developing malignant glaucoma. Follow them closely in the early postoperative period, because the early stages of the disease can be easily overlooked. IOP, that is, inappropriate for the clinical presentation of the eye could be an early sign of malignant glaucoma. For example, progressive shallowing of the AC associated with an IOP of 4 6 mmHg and slowly rising is consistent with the early diagnosis of malignant glaucoma (often the bleb is formed at this time).

The development of high resolution imaging techniques has proved helpful in the diagnosis and management of malignant glaucoma. The configuration of anterior segment structures can be assessed by using UBM (5,14,42 44,54) in order to preoperatively evaluate the risk of malignant glaucoma and establish a diagnosis of aqueous misdirection especially during the early postoperative period. In addition, slit-lamp adapted optical coherence tomography (OCT) (55), a new noninvasive high resolution imaging technique, may be helpful in recognizing the early stages of malignant glaucoma by objectively monitoring AC depth.

Once malignant glaucoma is suspected vigorous medical treatment should be initiated for 5 7 days.

5.2.Medical Treatment

Medical treatment may require 5 7 days for a response to develop, and is effective in50% of the cases (5,11) (Fig. 22.2). In 1962, Chandler and Grant (39) were the first to report successful relief of malignant glaucoma, by using mydriatic cycloplegic eyedrops. Cycloplegics tighten the zonules (39), pull the lens iris diaphragm backwards against the force of the vitreous and break the ciliary block (45) by relaxing the ciliary body muscle.

Additionally, in order to reduce the amount of aqueous humor that may be pooling posteriorly, its production should be decreased by using aqueous suppressants such as

carbonic anhydrase inhibitors (CAI), beta-blockers, and alpha two-agonists. The use of hyperosmotics, which was introduced in 1963 by Weiss et al. (56), should also be initiated for several days to reduce the amount of misdirected aqueous. Glycerol is given orally as a 50% aqueous solution at 1.0 1.5 g/kg body weight (note: a 100 cc bottle of 50% glycerol contains 50 g of glycerol; do not give to diabetics). Mannitol is given intravenously at 1 2 g/kg body weight over 45 min (note: a 500 cc bag of 20% mannitol contains 100 g of mannitol). Topical corticosteroids are used to reduce the uveal tract inflammation and minimize the risk of developing suprachoroidal effusion.

If the condition is relieved, aqueous suppressants can be cautiously withdrawn but only after many months of treatment. Hyperosmotics and CAIs are the first to be discontinued, followed by the alpha two-agonists (54). Be very cautious when stopping beta-blockers. We have seen recurrences occur on discontinuing beta-blockers. It is of great importance that the treatment with cycloplegic drops be continued indefinitely to prevent recurrences. A problem with long-term cycloplegia is sensitization to atropine drops (57,58). Hyoscine (scopolamine) drops can be used in place of atropine. The nonstructurally related cycloplegic agents such as tropicamide and cyclopentolate hydrochloride can also be used.

If medical treatment fails to reverse the aqueous misdirection and deepen the AC in 5 7 days, laser or surgery treatment is indicated. When there is lens cornea touch, surgery should be performed immediately, in order to prevent the formation of PAS, cataract, and damage to the corneal endothelium.

5.3.Laser Treatment

If the condition persists despite the earlier treatment attempts, then it is reasonable to try one of the noninvasive laser approaches. The choice of the appropriate laser procedure depends on whether the eye to be treated is phakic, pseudophakic, or aphakic.

The Nd:YAG laser has proven useful to disrupt the vitreous face and zonules when treating aphakic and pseudophakic malignant glaucoma (59 62). Do not attempt this procedure in phakic eyes. Nd:YAG laser disruption of the anterior hyaloid, which was suggested by Epstein et al. (59), creates communication channels through the previously impermeable vitreous face and re-establishes the anterior flow of aqueous. The Nd:YAG laser (3 11 mJ) can be applied through either the PI or the pupil, combined with capsulotomy. Try to disrupt the capsule and anterior hyaloid off centre, if possible. We have found the procedure works better the further away one disrupts the hyaloid from the centre of the IOL. If successful, anterior hyaloid photodisruption results in immediate deepening of the AC.

More recently, Carassa et al. (63) reported successful treatment of malignant glaucoma in five pseudophakic eyes with contact transscleral diode laser cyclophotocoagulation after failure of Nd:YAG laser hyaloidotomy. The treatment involved the application of 20 laser spots over 3608, 1.5 mm posterior to the limbus. The power employed was 4.0 J. The mechanism of action was attributed to coagulative shrinkage and posterior rotation of the ciliary processes. In addition, reduction of aqueous production due to ciliary body photocoagulation presumably contributes to curing the condition.

Herschler (64) reported successful relief of malignant glaucoma, in five of six cases, by Argon laser shrinkage of the ciliary processes. There is no indication if Herschler attempted the laser in phakic or pseudophakic eyes. Theoretically, this technique could be cautiously used in phakic patients. However, it is advisable to use this procedure only in pseudophakic and aphakic patients. Permanent argon laser shrinkage of two to four ciliary processes exposed through the PI effectively cured the condition, presumably