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Editors Selection IGR 9-4
Clinical Forms of Glaucoma: Surgical Treatment of NTG
Comment by Robert Feldman on:
74241 Effect of trabeculectomy on visual field progression in Japanese progressive normal-tension glaucoma with intraocular pressure < 15 mmHg, Naito T; Fujiwara M; Miki T et al., PLoS ONE, 2017; 12: e0184096
Naito et al. Effect of trabeculectomy on visual field progression in Japanese progressive normal-tension glaucoma with intraocular pressure < 15 mmHg.
Normal tension glaucoma (NTG) occurs when glaucomatous optic nerve damage is present with IOP in the "normal" range. It is the most common form of glaucoma in Japan, with a prevalence rate of 3.6%. Treatment for NTG is medication to lower IOP, with surgical intervention to further lower IOP if progression continues. The purpose of this study was to determine the efficacy of lowering IOP by trabeculectomy in decreasing the slope of mean deviation (MD) in patients with IOP < 15 mmHg.
The authors retrospectively reviewed records of 17 cases of NTG who had undergone trabeculectomy with mitomycin-C for progressive NTG with medically controlled IOP < 15 mmHg, 5 reliable visual field tests both pre- and postoperatively, and > 2 years follow-up. Cases where cataract surgery was done in conjunction with trabeculectomy or previous cataract surgery were included. Postoperative IOP was significantly lowered (mean reduction 5.8 mmHg, 41.7%) from preoperative IOP. In eyes with single-digit postoperative IOP, 91.7% showed improvement in MD slope, while only 20% with postoperative IOP > 10 mmHg showed MD slope improvement. Three eyes had decline in visual acuity > 0.1 logMAR units, and all 3 had hypotony maculopathy. Preoperative MD slope that could predict 50% improvement in postoperative MD slope was -0.91 dB/year. The group showing no improvement in MD slope had a significantly higher postoperative IOP, lower mean rate of IOP reduction, and used more IOP-lowering medications after surgery.
The authors concluded that achieving single-digit IOP by trabeculectomy results in slowing visual field progression in NTG patients. They cautioned that IOP < 7 mmHg could result in visual acuity decline. As with small retrospective studies, the usual limitations apply.
Additionally, visual field testing was not consistent, with some patients followed with a 30-2 test and others with a 10-2 test. Even though both groups showed delays in glaucoma progression, the two slope changes are not comparable.
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