“…Normal-tension glaucoma (NTG) is defined as chronic open-angle glaucoma with progressive optic nerve damage and corresponding visual field (VF) defect, despite an untreated intraocular pressure (IOP) that is always measured below 21 mmHg (Tanna & Krupin 2009). Several risk factors have been found to be associated with the prevalence and progression of NTG, such as IOP (CNTGS 1998a,b;Drance et al 2001;Nakagami et al 2006;Aoyama et al 2010), central corneal thickness (Morad et al 1998;Copt et al 1999), disc haemorrhage (Daugeliene et al 1999;Ishida et al 2000;Drance et al 2001;Park et al 2009), disc size (Tuulonen & Airaksinen 1992;Tomita et al 1994;Jonas et al 1995), betazone peripapillary atrophy (Jonas & Xu 1993;Park et al 1996;Daugeliene et al 1999;Kawano et al 2006), myopia (Perkins & Phelps 1982;Drance et al 2001;Suzuki et al 2006;Araie et al 2012) and ocular perfusion pressure (Sung et al 2009(Sung et al , 2011. Of these, IOP is the only modifiable risk factor and has been an important target of NTG treatment.…”