Normal-tension glaucoma: Strategies for management

March 20, 2013

Normal-tension glaucoma (NTG) is a very complex disease. There seem to be both IOP-dependent and IOP-independent mechanisms. David Greenfield, MD, outlines his four-point strategy for managing NTG.

 

Miami-Glaucoma can progress over time in untreated patients but also in treated patients. David Greenfield, MD, outlined his four-point strategy for managing normal-tension glaucoma (NTG).

“The Collaborative Normal Tension Glaucoma Study [CNTGS] found that even in eyes with a 30% IOP decrease, there was still 20% progression over the course of 5 years,” said Dr. Greenfield, professor of ophthalmology, Bascom Palmer Eye Institute, Miami.

While IOP lowering prevents progression in some patients, other findings in glaucoma studies are that a predetermined target IOP is associated with lower progression rates, progression occurs despite treatment, and progression can occur in patients with normal IOP values. This happens because many factors seem to affect the health of the retinal ganglion cells, i.e., increased IOP, ischemia, aberrant immunity, and neurotropin deficiency, among others.

First, Dr. Greenfield considers if the glaucoma is truly progressing.

“It is essential to confirm suspected visual field progress in all patients,” he emphasized. More than three confirmatory tests are required.

Second, he determines if the damage is from glaucoma or a non-glaucomatous etiology, such as pituitary adenoma, dominant optic atrophy, trauma, pituitary apoplexy, arteritic anterior ischemic optic neuropathy, or optic neuritis.

“There are many retinopathies and optic neuropathies that can mimic the type of optic neuropathy that we see in NTG,” he cautioned.

Third, scanning can help determine the etiology responsible for progression by identifying specific characteristics of a pathology that differ from the characteristics of low-tension glaucoma.

Fourth, and most importantly, in his management strategy, he attempts to achieve a 30% reduction in IOP from the baseline value.

The CNTGS found that this goal is achievable about 50% of the time. Because no beta-blockers, alpha-2 adrenoreceptor analogues, or prostaglandin analogues were used in that study, Dr. Greenfield pointed out, non-surgical IOPs likely can be achieved in from 75% to 80% of patients.

He offered the caveat that the 30% reduction is inadequate in some patients who have rapidly progressing glaucoma, scotomas close to the fixation point, or long life expectancy.

When differentiating patients who require surgery from those who can be treated medically, he noted that most patients do not require surgery and 50% do not have progression. He advised caution about aggressive IOP lowering in patients who have high myopia, the elderly, and those receiving anticoagulant medications.

Surgery, i.e., trabeculectomy or implantation of a drainage device, may be required in young patients, patients with rapid progression, those with progression despite an IOP of 12 mm Hg or lower, monocular patients, and in those with a threat to fixation. Dr. Greenfield’s surgery of choice is trabeculectomy with an anti-fibrosis agent.

“NTG is a very complex disease. There seem to be both IOP-dependent and IOP-independent mechanisms. IOP reduction is the only proven therapy. Luckily, most patients have a response to non-surgical therapy,” Dr. Greenfield concluded.

This article was adapted from Dr. Greenfield’s presentation during Glaucoma Subspecialty Day at the 2012 American Academy of Ophthalmology annual meeting.

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