Daniel Driscoll, M.D.
Contributing Editor
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Neovascular glaucoma (NVG) is a devastating eye disease that often presents acutely in the setting of prior ocular pathology. Patients often present to our triage department late in the day after attempted management at an outside eye care facility with painful, swollen, erythematous eyes that are refractory to topical ocular hypotensive medications. Intraocular pressures are often significantly elevated, ranging from mid thirties to over seventy.
It has long been known that the physiologic cause for intraocular pressure rise in neovascular glaucoma is vascular proliferation in the angle, causing obstruction of aqueous outflow. Retinal ischemia causing increased VEGF drive is the underlying pathology responsible for the neovascular proliferation throughout the eye, not limited to only the angle. The most common etiologies for ocular ischemia encountered in patients at our facility include type II diabetes and central retinal vein occlusion, with minor contributions from diabetes type one and ocular ischemic syndrome.
The goal of care for NVG patients in the acute setting is threefold: 1) Reduce intraocular pressure; 2) Reduce VEGF production by the ischemic tissue; 3) Make the patient comfortable. Patients presenting with NVG are usually triaged to the “more urgent” strata and immediately started on topical ocular hypotensive medications. This therapy is often combined with oral medications including acetazolamide and hyperosmotics such as glycerin (unless medically contraindicated). Topical and oral medical therapies are often met with decreases in intraocular pressure, sometimes to normative values. However, it must be emphasized that these therapies are temporizing; the true cause for the underlying pressure increase must be treated, namely increased VEGF.
Recently, Rauscher et al. studied the different types and timing of treatments for neovascular glaucoma. The goals of the study were to examination outcomes of vision, timing to glaucoma drainage implant use, and the effect of intravitreally injected anti-VEGF modulating medication (bevacizumab) alone or in combination with pan-retinal photocoagulation (PRP), the standard non-surgical therapy for neovascular glaucoma. Patients were randomized into those that received intravitreal bevacizumab and those that did not, independent of all other therapies. Treatment characteristics included number of bevacizumab injections, visual acuity, intraocular pressure, and sessions of PRP.
Results of the study showed a trend for patients receiving intravitreal injections of bevacizumab to require fewer ocular hypotensive medications at one year follow up. There was also a tendency towards earlier glaucoma drainage implant placement within the first six months for patients that did not receive intravitreal bevacizumab. Patients receiving bevacizumab had lower intraocular pressures significant only at the twelve month follow-up window. 100% of the bevacizumab arm achieved HM or better vision at three months compared to 80% of non-injected patients (p=0.003), however these levels reversed by twelve months follow-up for unclear reasons.
Essentially, Rauscher showed that intravitreal bevacizumab is a temporizing measure for causing regression of neovascularization of the iris and angle; however all eyes should still receive PRP, a proven and more-permanent non-surgical treatment for NVG. Pitfalls to treatment with bevacizumab include a significant increase in the rate of hyphema and the tendency to delay PRP.
Triage patients are examined for signs of NVI/NVA prior to dilation and then undergo fundoscopic examination by the emergency room physician. Media clarity is the most important determinant of which course of therapy to pursue. In the setting of minimal to no hyphema, and negligible lenticular and intravitreal obscuration, immediate PRP is the therapy of choice. Given that the treatment goal is to minimize VEGF drive, PRP is usually administered in quantities greater than traditional therapy for proliferative diabetic retinopathy. The physician must carefully weigh factors such as patient pain tolerance and likelihood to follow-up with prevention of choroidal edema. PRP treatment administration experiences have yielded superior results using the pattern scan laser (PASCAL) in combination with a pan-fundus lens such as the H-R WideField™ Laser Lens from Volk. Patients appear to tolerate the procedure much better than with traditional argon laser due to shorter burn times, larger treatment spot size, and the ability to treat in multiple locations simultaneously, thereby decreasing total treatment time. In the instances that patients cannot tolerate laser, peribulbar block may be administered.
Following PRP, intraocular pressure is again assessed. Normally, at least a day is required before the hypotensive effects of PRP are seen. Generally, pressures less than thirty are discharged home on topical and oral therapy with strict instructions for follow-up the next day. Patients with pressures that remain elevated above forty may be temporized with anterior chamber paracentesis, although this carries a high rate of complicating hyphema. Once the pressure is temporized, the physician then has the option of intravitreal bevacizumab injection on the same initial emergency visit. Post-injection pressure spikes are very common, necessitating close monitoring in the emergency department. If the pressure does not sufficiently lower itself in the first hour after injection, a therapeutic anterior chamber paracentesis is usually attempted.
Patients with NVG are instructed to follow-up daily for IOP checks, additional PRP and injections, and may ultimately require urgent glaucoma drainage implant placement when the aforementioned therapies fail. Neovascular glaucoma is a visually destructive disease often resulting in very poor visual outcomes. Treating physicians often consider preservation of hand-motion vision a victory in the setting of such dismal visual prognosis. Prompt and appropriate treatment of neovascular glaucoma in the emergency setting will set the stage for successful preservation of hand motions vision, or better.
The author would like to give special recognition to Fred Rauscher, MD, for his research regarding the efficacy of intravitreal bevacizumab in the setting of neovascular glaucoma.
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