Purpose: To evaluate the consistency of the definition of normal-tension glaucoma (NTG).
Methods: All articles about NTG published between 1973 and 1997 from three clinical journals of ophthalmology were identified by a literature search. They were reviewed to determine criteria used to define NTG, including optic nerve assessment and intraocular pressure (IOP) requirements.
Results: There were 63 articles identified that defined the disease entity NTG, including 30 published between 1973 and 1992 and 33 published between 1993 and 1997. Maximum IOP values acceptable for designation as NTG ranged from 17 mmHg to 26 mmHg. A significantly greater proportion of studies published during the last 5 years required maximum IOP values < or = 21 mmHg. Inclusion criteria based on structural characteristics of the glaucomatous optic disc or on the glaucomatous visual field were present in 55 (87%) and 56 (89%) articles, respectively. Of the seven articles that listed specific features classifying a disc as glaucomatous, seven (100%) were published within the last 5 years. Of the 13 articles that listed specific features classifying a field as glaucomatous, 9 (69%) were published within the last 5 years.
Conclusion: The criteria used to define NTG during the last 25 years have been highly variable. However, publications during the last 5 years have been more likely to require a maximum IOP < or = 21 mmHg and to describe specific features of the glaucomatous optic disc and visual field.