Ординатура / Офтальмология / Английские материалы / Clinical Pathways in Glaucoma_Zimmerman, Kooner_2001

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322 Neovascular Glaucoma

Table 14–1 Disorders Predisposing to NVG

Systemic vascular disease

Carotid occlusive disease

Carotid cavernous fistula

Giant cell arteritis

Sickle cell disease

Ocular vascular disease

Diabetic retinopathy

Central vein occlusion

Central artery occlusion

Branch vein occlusion

Coats’ disease (retinal telangiectasia)

Eales’ disease

Retinopathy of prematurity

Persistent hyperplastic primary vitreous

Anterior segment ischemia

Other ocular disease

Chronic uveitis

Chronic retinal detachment

Primary rhegmatogenous

Sticklers’ syndrome

Retinoschisis

Trauma

Endophthalmitis

Intraocular tumor

Uveal melanoma

Metastatic carcinoma

Retinoblastoma

Therapy

Radiation treatment

Postvitrectomy diabetic eye

What Are the Biologic Characteristics of Patients Who

Have NVG?

There is no particular blood level of antibodies, chemicals, enzymes, or cellular constituents that is diagnostic of NVG. However, patients may demonstrate systemic features consistent with their underlying etiology. Diabetics may be poorly controlled with elevated serum glucose. Patients with carotid occlusive disease often have concomitant heart disease, hypertension, and significant obstruction on carotid Doppler testing. Glaucoma is a risk factor for central retinal vein occlusion (CRVO).

What Are the Social And Economic Factors of Patients

Who Have NVG?

Effective prevention and treatment of NVG is dependent on timely diagnosis and management. Thus, social and economic factors predisposing to poor compliance and follow-up must be considered.

What Are the Personal Habits of Patients Who May

Develop NVG?

There are no personal habits such as tobacco use, diet, or physical exercise likely to contribute to the development of NVG. A history of noncompliance with medical treatment is a risk factor for late detection of NVG.

What Are the Genetic Characteristics of Patients Who

May Develop NVG?

There are no genetic characteristics that favor the development of NVG.

What Are The Major Entities that Lead to NVG?

The medical literature contains many possible etiologies to consider in patients with NVG, but diabetes mellitus, CRVO, and ocular ischemic syndrome (OIS) are the primary underlying diseases to consider. There are two large epidemiologic studies on the causes of NVG (Table 14-2). The Madsen2 study reviewed hemorrhagic glaucoma in 70 patients in a Denmark eye facility. The Brown et al3 study is a retrospective review of 208 patients with NVG in a major urban eye hospital.

What Is the Pathogenesis of NVG?

NVG is a complication thought to be secondary to angiogenic factors produced by the ischemic retina that enter the anterior chamber.1 Various substances have been suggested as the underlying common agent. Of note, vascular endothelial growth factor (VEGF) has been shown to induce a noninflammatory iris neo-

Table 14–2. Etiology of NVG in Epidemiologic Studies

324 Neovascular Glaucoma

vascularization in nonhuman primate eyes when injected at a concentration comparable to that found in human eyes with neovascular glaucoma.4 There is evidence that the angiogenic factor originates from the posterior segment of the eye. NVG has been observed following noncomplicated laser posterior capsulotomy, which presumably permitted angiogenic factors access to the anterior chamber.5 Additionally, neovascularization of the iris (NVI) has been observed to begin at the peripheral iridotomy site in a patient with iris bombé.6

Diagnosis and Differential Diagnosis

How Is NVG Diagnosed?

In the classic presentation of fulminant NVG, patients complain of pain, photophobia, and decreased vision. Visual acuity is typically in the hand motion to counting fingers range. The secondary closed angle results in extremely high intraocular pressure (IOP), producing conjunctival injection, steamy cornea, and inflammation. Slit-lamp examination demonstrates NVI and ectropion uvea (a flattened iris anterior face and rotation of the iris pigment epithelium anteriorly). Gonioscopy reveals angle closure, with the inferior portion being the last to seal off. Fundus examination often shows an ischemic retina and thus the underlying disorder.

There may be great variability in clinical presentation in each individual case of NVG. For example, IOP may be normal or reduced in NVG secondary to OIS.

How Is NVI Differentiated from Normal Iris Vasculature?

Abnormal iris vessels have characteristic features that differentiate them from normal iris vessels. Normal iris vessels have a nonarborized intrastromal orientation. Iris neovascularization first appears as buds of vessels, resembling glomeruli. These buds are typically detected first at the pupillary margin. Later stages of NVI show a fine net of blood vessels in an extrastromal location. NVI typically demonstrates angiographic leakage, whereas normal iris vessels do not leak. Any blood vessels that cross the sclera spur are considered abnormal. Later stages lead to arborization into the trabecular meshwork, giving the meshwork a red appearance. It may be difficult to differentiate engorged iris vessels in an inflamed eye from NVI.

How Does the Neovascularization of the Angle Lead to Angle Closure?

Posterior segment hypoxia leads to the production of angiogenic factors that circulate into the anterior segment, stimulating the growth of new blood vessels, usually first at the pupillary margin. It is classically thought that neovascularization of the angle (NVA) does not occur without accompanying NVI, though there are anecdotal accounts that dispute this claim. For example, gonioscopy may detect NVA prior to the detection of NVI.7

Pathologic studies have confirmed the presence of an accompanying “invisible” fibrovascular membrane in cases of NVG. Contraction of this fibrovascu-

lar membrane leads to points of synechial angle closure. Coalescence of these points of synechial closure ultimately leads to total angle closure and thus dramatic reduction of trabecular outflow. The progression of NVI to NVA to NVG may occur over days, weeks, months, or years.

What Is the Differential Diagnosis of NVG?

In its early stages, NVG must be differentiated from other disorders with prominent iris blood vessels. There are a number of historical and clinical features that may facilitate this distinction (Table 14-3).

In the fulminant stage, the main differential diagnosis to be considered is acute primary angle closure because it shares with NVG the common features of poor vision, extreme pain, high IOP, congested conjunctiva, and steamy cornea. If examination of the fellow eye also reveals a narrow occludable angle, then a diagnosis of primary angle closure is more likely. Also, pressure on gonioscopy (compression gonioscopy) may force the angle open. In NVG, the angle is sealed and cannot be forced open. Funduscopic exam in NVG is consistent with a hypoxic posterior segment.

What Are the Key Distinguishing Features of the Main

Causes of NVG?

This chapter discusses differentiating between the most likely entities in patients with NVG (Table 14-4). Chapter 11 discusses the primary etiologies of central retinal vein occlusion, diabetes mellitus, and OIS.

Treatment and Management

What Are the General Principles to Consider in Preventing Progression to NVG?

It is crucial to maintain a high clinical suspicion for the potential of the currently managed disease to progress to this complication (Fig. 14-1). Prompt recognition of iris neovascularization is critical to successful management. This is best achieved with standardized high-magnification nondilated examination of the iris, with particular attention to the pupillary margin.

326 Neovascular Glaucoma

Table 14–4. Differential Features of the Predominant Etiologies of NVG

When NVI is detected, determine and treat the underlying cause of posterior segment hypoxia. If examination reveals a fundus without definite hypoxia, always consider the diagnosis of OIS. The goal is to reduce posterior segment hypoxia and thus regress the NVI and NVA before it reaches fulminant NVG.

What Are the Techniques Used to Prevent Progression to NVG?

Panretinal photocoagulation is the preferred means of decreasing posterior segment hypoxia, but it is limited because successful treatment is largely dependent on clear media. Topical glycerin may be used to decrease corneal edema so that one may achieve sufficient improved view for effective treatment. The goal of treatment is to ablate the ischemic retina. Insufficient treatment will not adequately reduce the hypoxic drive to NVG progression. The effectiveness of panretinal photocoagulation in NVI and NVG has been well documented.8,9

Panretinal cryotherapy may be useful in cases where the cornea, lens, or vitreous is too hazy to get adequate laser treatment. The disadvantage of this

328 Neovascular Glaucoma

How Is a Patient with Diabetic Retinopathy Prevented from Progressing to NVG?

Prompt panretinal photocoagulation should be employed when high-risk proliferative features are found in diabetic eyes. The Diabetic Retinopathy Study demonstrated that vitreous hemorrhage, disc neovascularization, and new areas of retinal neovascularization are ominous features of proliferative diabetic retinopathy.11

Particular caution should be employed in diabetic patients who are status post-cataract surgery or postvitrectomy, as they may quickly progress to fulminant NVG. It is thought that preservation of the posterior capsule during cataract surgery minimizes the risk of worsening retinopathy. The incidence of NVG complicating vitrectomy has been decreasing, presumably due to better equipment and endolaser treatment.12 Systemic features such as hypertension and renal failure are often found concomitantly in diabetics who progress to NVG.

How Is a Patient with Newly Diagnosed CRVO

Prevented from Progressing to NVG?

Important data regarding the history of treated and untreated CRVO have been reported by the CRVO study group.13 Particular observations to consider include:

1.One-third of initially perfused CRVO may progress to ischemia over 3 years.

2.Initially nonperfused CRVO is at 35% risk of developing NVI/NVA.

3.Panretinal photocoagulation should commence when NVI/NVA develops.

Differentiating between ischemic and nonischemic status may be difficult secondary to retinal obscuration by retinal hemorrhage. Poor visual acuity, presence of an afferent pupillary defect, and decreased electroretinogram values have also been reported to be predictive of progression to neovascular disease.14 Recommended follow-up schedules may be guided by visual acuity at presentation, as per the guidelines of CRVO study group’s report:

•20/40 or better: every 1 to 2 months for the first 6 months;

•20/50 or worse: every month for the first 6 months;

•worsening visual acuity: an ominous sign of progression to ischemic status.

Undilated gonioscopy should be done at each follow-up exam because NVA may develop prior to NVI.7

How Is a Patient with OIS Prevented from Progressing to NVG?

Always consider this diagnosis in cases when the funduscopic exam does not show profound clinical evidence of retinal ischemia or when panretinal photocoagulation does not regress NVI/NVA. Some studies report that only a third of these patients have elevated IOP.1 This decrease in aqueous production is thought to be due to hypoperfusion of the ciliary body. Panretinal photocoagu-

lation should be the first step, though it may not be effective, because OIS also gives rise to anterior segment ischemia late in its course.15 Once surgical revascularization of the carotid occurs, it may lead to an increase in IOP and worsened ophthalmic vessel disease. Internal medicine or cardiology services should be consulted in these patients to rule out carotid disease and concomitant cardiovascular disease.

The Underlying Cause of the NVG Was Diagnosed

and Treated and the IOP Is Now Within Normal Limits. What is Next?

Close monitoring and observation are essential because this condition may recur at any time.

What Treatment Options Are Available If the IOP Is Still Elevated Following Complete Treatment of the Underlying Cause of NVG?

The IOP may still be elevated because despite inducing the NVI/NVA to quiescence, the angle is still zipped shut and a permanent angle closure status is maintained. Medical therapy is the preferred means of controlling IOP at this point.

Ocular pressure reduction medications may also be used to obtain a clearer view for diagnostic and treatment purposes. The aim is to maintain acceptable IOP. Avoid pilocarpine and other cholinergics, because they may break down the blood vessel barrier and facilitate increased inflammation. Topical corticosteroids are helpful in reducing inflammation and may be used as indicated.

What Treatment Options Are Available If, Despite

Maximally Tolerated Antiglaucoma Medications, the IOP

Is Still Elevated?

NVG typically responds poorly to conventional glaucoma surgery. These poor outcomes have prompted a variety of different interventions strategies. The main approaches used are trabeculectomy with antimetabolites, tube-shunt surgery, cyclocryotherapy, and cyclophotocoagulation. In an eye with quiescent neovascularization, trabeculectomy with antimetabolites is considered by many to be the primary option. If there are active vessels present, tube-shunt versus ciliary body ablation is considered (see Chapter 19).

What Are the Data Regarding Success Utilizing

Trabeculectomy?

Trabeculectomy without metabolite and without concomitant retinal ablation has a low rate of NVG regression (10–30%), whereas, with panretinal photocoagulation as a preoperative adjunct, a 67% success rate has been reported at 12-month follow-up.16