2020–2021 BCSC Basic and Clinical Science Course™
Chapter 7: Primary Open-Angle Glaucoma
Open-Angle Glaucoma Without Elevated IOP (Normal-Tension Glaucoma, Low-Tension Glaucoma)
NTG can be mimicked by conditions other than glaucoma. It is therefore essential to distinguish glaucoma from other optic neuropathies (eg, optic nerve drusen, ischemic optic neuropathy) because appropriate therapy will differ (Table 7-2). Visual field defects in some of these conditions may appear similar to those seen with NTG and can even be progressive.
Patients with “normal” IOP in clinic may experience higher pressures outside clinic hours. Diurnal IOP measurement may therefore help in the determination of target IOPs by identifying peak IOPs and IOP fluctuation, but it does not capture nocturnal patterns of IOP. Also, elevated IOP can be obscured in patients taking systemic medication, particularly systemic β-blockers. In addition, some patients with apparent NTG may have artifactually low tonometry readings because of altered corneoscleral biomechanics, 1 marker of which may be a thin central cornea. Similarly, decreased corneal thickness in patients who have undergone refractive surgery may result in underestimation of true IOP.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.