A diagnosis of normal-tension glaucoma can be hard to pin down

September 1, 2011

Article

Over the years, normal-tension glaucoma has become a more recognized clinical entity.

Atlanta-Over the years, normal-tension glaucoma (NTG)-once an enigmatic disease-has become a more recognized clinical entity, according to Anthony Litwak, OD, FAAO, speaking here at the annual SECO meeting.

Clinical clues

Clinical features often associated with NTG include acquired optic pits of the optic nerve, which are usually associated with a corresponding visual field defect that tends to be closer to fixation and may progress more rapidly, Dr. Litwak said. In addition, peripapillary changes are more common in NTG than POAG and are usually associated with thinning of the adjacent neuro-rim tissue, but their specificity for glaucoma is not known.

Optic disc hemorrhage occurs in up to 23% of glaucoma patients, also more frequently in those with NTG than high-tension glaucoma.

"When I see a disc hemorrhage in a glaucoma-uspect patient, that's usually enough evidence for me to start treatment," Dr. Litwak said. "If a patient is already being treated for glaucoma and develops a disc hemorrhage, that's usually a sign that the disease is progressing."

Other signs that are more common in NTG than in high-tension glaucoma are focal notching of the optic nerve, which usually corresponds to focal wedge nerve fiber layer defects, and localized visual field defects that have steeper slopes and are closer to fixation.

Differential difficulties

Dr. Litwak also discussed the differential diagnosis of NTG. One culprit can be POAG, especially in cases where IOP is measured in the statistically normal range due to diurnal fluctuation, IOP-lowering effects of oral medications such as hypertensive agents, or previous use of oral or topical steroids. Thinner corneas will result in a lower Goldmann applanation IOP reading.

A large cup does not necessarily mean glaucoma, as the physiological cup size is directly related to the overall disc size. A mismatch between cup and disc size, such as a small disc with a medium-size cup or a large cup with a medium-size disc, is more significant than a big cup in a large nerve, he said.

Treatment options

Treatment for NTG should be considered when there are signs of definitive optic nerve damage, a new disc hemorrhage, a visual field defect threatening fixation, or progression of the visual field defect, which may require several visual fields to confirm.

As with patients diagnosed with high-tension glaucoma, IOP lowering is beneficial in patients with NTG, and a reduction of 30% from baseline is an initial recommendation based on the Collaborative Normal-tension Glaucoma Study, explained Dr. Litwak. Prostaglandins, alpha agonists, topical carbonic anhydrase inhibitors, and laser trabeculoplasty are appropriate treatment options, while the use of nonselective beta blockers to treat NTG is controversial.