• 27 chapterGlaucoma Neovascular

INTRAOCULAR TUMORS

Malignant melanoma

The incidence of NVG with malignant melanoma is not high, and malignant melanoma as a cause of NVG is relatively low on the list of differential diagnosis. Nevertheless, in an eye with NVG in which the posterior segment is not visible because of opaque media, malignant melanoma must be considered, especially in the absence of DR in the contralateral eye or a history of CRVO in the ipsilateral eye.

Retinoblastoma

Walton and Grant27 found 38 of 56 children with NVI to have retinoblastomas and that the duration of the tumor was associated with the development of NVI. They also reviewed 88 eyes enucleated for retinoblastoma and found that 39 (44%) had histologically confirmed NVI, with a significant association between the presence of NVI and choroidal involvement by the tumor.

Ultrasound, computed tomography, magnetic resonance imaging, and other appropriate studies must be performed. Iris neovascularization has also been described in eyes with metastatic tumors and reticulum cell sarcoma. In these cases the direct effect of tumor-secreted angiogenesis factor may be the cause of the new vessels.28

MISCELLANEOUS CAUSES

There are several common pathways, such as chronic retinal detachment and extensive capillary nonperfusion with resultant retinal hypoxia. These include Stickler’s syndrome, Wagner–Stickler’s syndrome, autosomal-dominant neovascular inflammatory vitreoretinopathy, and retinopathy of prematurity. More localized anterior-segment perfusion compromise has been shown to be the cause of NVI in Fuchs’ heterochromic iridocyclitis and exfoliation syndrome. The association between scleritis and NVG is also probably due to secondary vascular occlusion. Other miscellaneous retinal conditions that may be associated with the development of NVG include Coat’s disease, Eales’ disease, giant-cell astrocytoma of the retina, and X-linked retinoschisis.

DIAGNOSIS AND ANCILLARY TESTING

The key aim in the treatment of NVG is early diagnosis so that the optimal treatment regimen can be instituted. Every patient with NVG should undergo a comprehensive medical and ocular evaluation with particular attention to the pupil, slit-lamp, gonioscopic, and dilated fundus examinations. The IOP should be measured if at all possible by applanation tonometry. A nondilated slit-lamp examination including gonioscopy is vitally important to detect early angle neovascularization and early anterior synechiae. Sometimes a few cells may be seen in the anterior chamber, which may erroneously be diagnosed as a sign of uveitis. Other methods, including angiography and electroretinography, have been described to detect subclinical anterior-segment neovascularization in patients at risk for rubeosis. Angiographic examinations of the iris, angle, and retina have been used in an attempt to predict the development of rubeosis. Iris fluorescein angiography shows a leakage of fluorescein from NVI (Figure 27.4). The electroretinogram measures a mass electrical response of the retina, allowing for assessment of the retinal periphery, which cannot be seen with fluorescein angiography. The electroretinogram can measure the degree of retinal ischemia, and its reading can then be correlated to the likelihood of rubeosis developing.

DIFFERENTIAL DIAGNOSIS

Iris and angle neovascularization (sometimes with hyphema) is occasionally present in Fuchs’ heterochromic cyclitis, but progression to

Figure 27.4  Iris fluorescein angiography demonstrates leakage of fluorescein from neovascularization of the iris in a case with Coats’ disease and neovascular glaucoma.

NVG is extremely rare. Very thin nonprogressive iris neovascularization can be observed at the pupillary margin in pseudoexfoliation syndrome, myotonic dystrophy, abnormal insulin secretion, and in elderly normal subjects. In acute iridocyclitis and after ocular surgery (particularly in diabetic patients), the engorgement of iris vessels can mimic fulminant NVG, but this rapidly resolves with topical steroids. Advanced NVG may be confused with acute angle closure glaucoma, but gonioscopy of the fellow eye generally shows a nonoccludible angle. Other causes of hyphema and ghost-cell glaucoma should be excluded.

SIGNS AND SYMPTOMS

The first visible signs of incipient NVG are tiny tufts of new vessels at the pupillary margin, site of the maximum turnover of aqueous containing specific growth factors. As NVI progresses, new vessels extend from the peripupillary tufts in an irregular, meandering manner. New vessels, at least clinically, characteristically appear on the surface of the iris. When new vessels reach the iris collarette, the collarette vessel, which is often normally present but not visible, may become engorged and appear as part of the NVI. In the more advanced stages, it is common to see effacement of the normal iris surface architecture, resulting in a relatively smooth iris. When these new vessels reach the angle, they cross the ciliary body band and scleral spur to arborize on the trabecular meshwork. At the angle, the larger vessels, after crossing the scleral spur, arborize with very fine capillaries over several clock-hours of the trabecular meshwork.

Until angle neovascularization covers a signicant portion of the trabecular meshwork, the IOP may be normal. The angle neovascularization is associated with fibrous tissue, and the fibrovascular membrane, which is invisible on gonioscopy, may block enough of the trabecular meshwork to cause open-angle glaucoma.

The fibrovascular membrane contracts, pulls the new vessels taut, and draws the iris root near the trabecular meshwork, determining mydriasis and focal and subsequently diffuse PAS. The new vessels can also spread over the anterior lens surface, with rapid cataract formation.

The eye is painful and photophobic. Vision is usually at the counting fingers to hand motion level, and the IOP may be as high as 60 mmHg or greater. There is a moderate to marked conjunctival congestion frequently associated with a steamy cornea, through which NVI and ectropion uveae are often visible. There are variable degrees of synechial angle closure observed gonioscopically.