Discrete Openangle Glaucomas

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The term ''primary open-angle glaucoma'' refers to a condition characterized by elevated IOP and characteristic optic disk and/or visual field damage with no other identifiable cause at slit-lamp examination. However, the use of the word ''primary'' is suggestive of a single, discrete entity with a specific mechanism of disease causation. More likely, this category represents an assortment of disorders, as we are now seeing with the discovery of multiple genetic loci. Similarly, the term ''normaltension glaucoma'' (or ''low-tension glaucoma'') has been used to define a group of patients with glaucomatous damage but IOP less than some arbitrarily defined number. This is an artificial distinction based on population statistics. Interpretation of this term as previously used in the literature is further complicated by the recent realization that Goldmann tonometry is influenced by corneal thickness, a factor not routinely measured previously. The term ''idiopathic open-angle glaucoma,'' which reflects the present state of ignorance about the cause of the disease, would be more appropriate. As specific causes are discovered and named, the pool of idiopathic glaucoma patients will gradually decrease in size.

The concept of primary and secondary glaucomas is more a reflection of incomplete understanding regarding the pathophysiologic events that ultimately lead to glaucomatous optic atrophy and visual field loss than of any true division of the glaucomas into primary and secondary forms.23 The term "discrete glaucomas'' is used here to refer to well-defined entities for which there is a better understanding of causation and associated ocular findings. In the past, treatment of these glaucomas has been virtually identical to that of idiopathic (primary) open-angle glaucoma. This singularity of treatment was unfortunate, because it reduced the emphasis on accurate diagnosis and delayed the development of disease-specific treatment modalities. The sections that follow emphasize the differences in treatment of discrete glaucomas from that of idiopathic open-angle glaucoma. Some of these differences are inferential, based on logic and empirical findings, and have yet to be proven in clinical trials.

12.2.1 Pigmentary Glaucoma. Pigment dispersion syndrome (PDS) and pigmentary glaucoma (PG) are characterized by disruption of the iris pigment epithelium (IPE) and deposition of the dispersed pigment granules throughout the anterior segment. The classic diagnostic triad consists of

1. Corneal pigmentation (Krukenberg spindle)

2. Slitlike, radial, midperipheral iris transillumination defects

3. Dense trabecular pigmentation

The iris insertion is typically posterior, and the peripheral iris tends to have a concave configuration. The extent of iridolenticular contact is greater than normal, inhibiting aqueous equilibration between the posterior and the anterior chamber by preventing retrograde aqueous flow. Inhibition of blinking allows buildup of the aqueous in the posterior chamber. The act of blinking provides a mechanical pump to push aqueous from the posterior chamber to the anterior chamber.24 Once in the anterior chamber, the increased aqueous volume or pressure pushes the iris backward, accentuating the concavity—a phenomenon termed reverse pupillary block.25 Accommodation also increases the iris concavity (figure 12.3A).26-28 Iris pigment is released by mechanical damage to the IPE due to friction between the posteriorly bowed iris and the anterior zonular bundles.

Treatment may be directed at lowering IOP or stopping the basic disease process. We do not generally treat normotensive patients. If IOP is elevated and pigment is noted in the anterior chamber either spontaneously or after dilation, then treatment is initiated. A case may be made for treating younger patients with high-normal IOP, but no prospective clinical trial of medical therapy or laser iridotomy has yet been performed.

Miotic therapy reverses the iris concavity and produces a convex configuration, completely eliminating iridozonular contact (figure 12.3B). By so doing, miotics may prevent further pigment liberation and the development or progression of trabecular damage and glaucoma by immobilizing the pupil and may allow existing damage to reverse more readily. Most patients requiring therapy for PG are between the ages of 20 and 45 years and tolerate miotic drops or gel poorly because of intolerable accommodative spasm, induced myopia, and blurred vision. Pilocarpine Ocuserts, which provided low-dose pilocarpine release at a constant rate and were well tolerated, are no longer manufactured.

Figure 12.3. (A) Iris concavity in pigment dispersion syndrome. (B) Pilocarpine produces convex configuration. (C) Laser iridotomy produces planar configuration.

There is approximately a 7% incidence of retinal detachment in patients with PDS, irrespective of the presence or absence of glaucoma and of miotic treatment.29 Approximately 80% of patients with PDS are myopic. The incidence of lattice degeneration and full-thickness retinal breaks appears to be more common in eyes with PDS or PG than in the unaffected population, when the degree of myopia is compared.30 Before a miotic is prescribed for these patients, a thorough peripheral retinal examination should be performed and any retinal breaks or vitreous traction should be treated prophylactically.

In the absence of pilocarpine Ocuserts, we advocate treating patients with PDS and elevated IOP with prostaglandin analogs, to which this disease responds extremely well. Aqueous suppressants may lead to greater iridozonular contact by decreasing the volume of the posterior chamber, while decreased aqueous flow through the trabecular meshwork may allow greater blockage and dysfunction of the meshwork over the long term.31 In one short-term study, latanoprost was shown to lower IOP more effectively than timolol in patients with PG.32 It has also been noted that PDS seems to respond to epinephrine or dipivefrin with a greater mean drop in IOP than does any other glaucoma.29,33,34

Elimination of iridozonular contact and improvement of aqueous outflow rather than inhibition of its production are more desirable in preventing glaucomatous damage by reversing the pathophysiology of the disease. Laser iridotomy relieves reverse pupillary block by allowing aqueous to flow from the anterior to the posterior chamber and produces a planar iris configuration (figure 12.3C). Whereas pilocarpine completely inhibits exercise-induced pigment release and IOP elevation, iridotomy does so incompletely.35'36

If patients with PDS could be identified before they develop irreversible outflow obstruction, IOP elevation might be prevented with a prophylactic iridotomy. Before this treatment strategy can be recommended, however, diagnostic measures are needed to predict which patients with PDS have a sufficient risk of developing IOP elevation to justify the prophylactic iridotomy, and large, long-term trials are needed to prove that the iridotomy will prevent the eventual elevation of IOP. In a retrospective multicenter case series of 60 patients observed for a mean of 70.3 ± 26.0 months after iridotomy in one eye, no long-term benefit was observed.37 Because the purpose of iridotomy is to prevent further pigment liberation from the iris, patients should still be in the pigment liberation stage (younger than *45 years of age). If pigment is liberated into the anterior chamber with pupillary dilation, it is suggestive that the patient is still in this stage. Patients with uncontrolled glaucoma who are facing surgery are also poor candidates, because years may be necessary to achieve functional reconstitution of the meshwork. At present, we restrict iridotomy to patients who have elevated IOP with no damage or with early glaucomatous damage.

12.2.2 Exfoliation Syndrome. Glaucoma associated with exfoliation syndrome tends to respond less well to medical therapy than does idiopathic open-angle glaucoma, is more difficult to treat, is more likely to require surgical intervention, and has a worse prognosis. Patients with exfoliative glaucoma have higher IOP and more severe damage at the time of detection, and their glaucomatous damage progresses more rapidly, compared with patients with primary open-angle glaucoma.38 Patients with ocular hypertension who have exfoliation syndrome are twice as likely to develop glaucoma compared with patients without exfoliation.39

Treatment of exfoliative glaucoma is usually initiated with a prostaglandin analog or aqueous suppressants, similar to treatment of primary open-angle glaucoma. Latanoprost was more effective than 0.5% timolol40 and as effective as timolol-dorzolamide fixed combination41 in reducing IOP in patients with exfoliative glaucoma. On the other hand, as in PG, miotics may be a good choice of initial agent because they not only lower IOP and increase aqueous outflow but also, by inhibiting pupillary movement, decrease the amount of exfoliation material and pigment dispersed by iridolenticular contact. Miotics should enable the trabecular meshwork to clear and should slow the progression of the disease. However, many patients have nuclear sclerosis, and miotics may reduce visual acuity or dim vision sufficiently to create difficulty. Also, long-term use of miotics may lead to the development of posterior synechiae. We have found, however, that 2% pilocarpine taken at bedtime provides a nonreactive 3 mm pupil throughout the day without causing blurred vision for most patients.

Pupillary dilation in eyes with exfoliation syndrome may result in acute IOP rises accompanied by diffuse pigment dispersion in the anterior chamber.42,43

12.2.3 Corticosteroid-Induced Glaucoma. Glaucoma is most commonly associated with topical application of corticosteroids, but may also result from systemic administration. Topical corticosteroid creams, lotions, or ointments placed on the eyelids, face, or even remote sites may also be associated with IOP elevation,44,45 as may inhaled corticosteroids.46 Elevated IOP may also be produced by an increase in endogenous corticosteroids, as seen in adrenal hyperplasia or Cushing's disease.47 Because corticosteroids may be prescribed by general physicians and because some preparations are now available over the counter, physicians and patients alike should be educated regarding their potential risks.

Patients receiving corticosteroids may develop elevated IOP from days to years after initiating treatment.48 With topical corticosteroids, IOP elevation typically occurs within 2 to 6 weeks. However, the period required and the magnitude of the IOP rise appear to depend on many factors, including the potency and dosage of the preparation, the frequency of application, the route of administration, the presence of other ocular or systemic diseases, and the individual responsiveness of the patient. In rare cases, an abrupt rise in IOP has been reported after corticosteroid administration in eyes with open angles.49

The clinical features depend on the age at presentation. In infants and very young children, corticosteroid-induced glaucoma may resemble typical findings of congenital glaucoma, with enlarged, edematous corneas.50 In older children and adults, it is clinically similar to juvenile- or adult-onset idiopathic open-angle glaucoma. In patients with normal-tension glaucoma, the clinician should consider the possibility of damage from previously elevated IOP as a result of past corticosteroid use.

When corticosteroid-induced glaucoma is suspected, the agent of concern should be discontinued or used in a lower concentration. Alternatively, a weaker cortico-steroid or a nonsteroidal anti-inflammatory agent (e.g., diclofenac) should be substituted. If IOP remains elevated despite discontinuation, the therapeutic approach is identical to that used for idiopathic open-angle glaucoma. If elevated IOP results from a periocular depot corticosteroid injection, excision of the depot may be necessary. IOP elevation associated with intravitreal steroid injection can be controlled with medical therapy in the large majority of cases.51 Infrequently, surgical intervention is required, in the form of vitrectomy-assisted removal of the steroid, filtration surgery, or both. Steroid-releasing implants, however, often cause marked and intractable elevation of IOP, often requiring surgical treatment. Although laser trabeculoplasty may be less effective than in eyes with other forms of glaucoma, laser treatment may be attempted prior to surgical intervention in patients more than 40 years of age.

12.2.4 Neovascular Glaucoma. Medical treatment of neovascular glaucoma can be frustrating and is often ineffective. Panretinal photocoagulation (PRP) for prolif-erative retinopathy should be performed. When adequate PRP is performed early, there is extensive evidence for the regression of anterior segment neovascularization in eyes with central retinal vein occlusion and proliferative diabetic retinopathy. Adjunctive medical therapy with angiogenesis-inhibiting drugs may be useful and is under evaluation at this time. Control of blood sugar is also important because near-normal glycemia is associated with later development and lesser severity of diabetic retinopathy.52

When the angle is open, medical treatment for neovascular glaucoma includes aqueous suppressants, topical corticosteroids, and a cycloplegic. Pilocarpine has been considered relatively contraindicated because of its effect on the blood-aqueous barrier, but may be tried. Similarly, prostaglandin analogs may be tried cautiously in view of their reported association with disruption of blood-aqueous barrier and increased intraocular inflammation.

With extensive synechial angle closure, miotics are ineffective and should be considered contraindicated because of the inflammation and hyperemia they produce. Prostaglandin analogs and aqueous suppressants are beneficial but often do not lower IOP to a normal range. Hyperosmotic agents can be used intermittently. The most important medications remain topical cycloplegics and corticosteroids to decrease congestion and inflammation and prepare the eye for definitive surgery.

12.2.5 Iridocorneal Endothelial Syndrome. Patients with iridocorneal endothelial syndrome may require treatment for corneal edema, glaucoma, or both. The glaucoma can often be controlled medically in the early stages, especially with aqueous suppressants. Lowering IOP may also control the corneal edema, although the additional use of hypertonic saline solutions and soft contact lenses is often required. When medical control becomes ineffective as the disease progresses, surgical intervention is required. Argon laser trabeculoplasty is contraindicated.

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