Currently, lowering IOP is the only therapeutic goal of glaucoma management, which raises the question of what to do with normal-tension glaucoma (NTG) patients. A new study suggests clinicians should stay the course and lower their IOP even further, as even a few mm Hg reduction could have protective effects.

A TANK binding kinase 1 (TBK1) gene duplication is among the most common molecularly defined causes of normal-tension glaucoma (NTG). TBK1-associated glaucoma exhibits classic features of NTG: patients present with severe disease at a relatively early age and the majority have slow to moderate visual field progression. Even with seemingly normal IOP, the rate of visual field often correlates with the magnitude of IOP.

This retrospective, observational case series evaluated the medical records of seven members of a family with TBK1-associated NTG. The team assessed clinical features at diagnosis, throughout management (mean of 21.5±9.0 years) and during last follow-up, including age, IOP, central corneal thickness, optic nerve head appearance, and visual field mean deviation (MD).

At diagnosis, the researchers recorded a mean age of 35±7 years, an IOP of 16±2.1mm Hg, a cup-to-disc (C/D) ratio of 0.9±0.08 and a visual field MD of -9.0±8.9dB in the 14 study eyes. They noted that 28% of eyes had no visual field defects, another 28% had early visual field defects and 43% already had severe visual field defects.

Throughout management, the investigators found that patients experienced an average IOP reduction of 28%. They noted that 33% of eyes had stable visual fields, while 67% experienced slow to moderate progression. They documented an average change in visual field MD of -0.53±0.26dB/year, with no eyes having rapid progression greater than 1.0dB/year.

At final follow-up, the study authors saw a mean IOP of 11.5±2.9mm Hg and a C/D ratio of 0.94±0.4. They added that 21% had early visual field defects, 29% had moderate visual field defects and 50% had severe visual field defects. They concluded that 43% had met the criteria for legal blindness. 

Quist TS, Johnson CA, Robin AL, et al. Long-term follow-up of normal tension glaucoma patients with TBK1 gene mutations in one large pedigree. Am J Ophthalmol. January 24, 2020. [Epub ahead of print].