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Abstract #19047 Published in IGR 3-1
The 'not quite' natural history of normal-tension glaucoma
Caprioli J; Maguire MOphthalmology 2001; 108: 245-246
In this guest editorial, the authors comment on the naturalness of the paper from the Collaborative Normal Tension Glaucoma Study Group: natural history of normal-tension glaucoma. The authors first discuss the question of whether so-called normal-tension glaucoma (NTG) is a distinct diagnostic entity. They prefer the terminology of pressure sensitive and pressure insensitive glaucoma. However, it is difficult at the moment to classify glaucomas as such. In the study under discussion, 230 eyes of 230 subjects were enrolled. Ninety-two of these eyes had a threat of fixation. Forty-three were assigned to treatment. The remaining 49 were used for this study with an additional 111 subjects who were followed so that they could be entered into the clinical trial whenever there was progression. Of these 111, 55, or about half, progressed. And they again were assigned to treatment or non-treatment. After all these procedures, the study focused on 160 eyes of 160 subjects. And the original authors suggested that about 10% of patients per year show evidence of progression. The authors of this editorial feels that the term 'natural history' may not be appropriate. They give four reasons for this: 1. Because of the selection biases described earlier, the results probably represent a 'minimal' estimate of the rate of progressive damage in NTG. It may not be possible to generalize the results to both eyes of subjects in an unselected population with NTG. 2. The follow-up, given the slow rate of progression of glaucoma, even in this 'long-term' study, is relatively short. Although some subjects were followed for five to seven years, the mean follow-up was 3.8 years. If, as some would argue, this disease demonstrates episodic progression, the relatively short follow-up may miss significant progressive events that occurred outside the window of observation. 3. The rate of visual field progression, as determined by this study, is sensitive to the definition of progression. When the definition was changed from the 'four of five' criteria used in the primary analysis to the definition that led to randomization, the six-year progression rate increased from 45-62%. It would seem that the same definition of progression that led to randomization should be applied to the detection of progression in this untreated arm of this study. 4. The regression of the visual field mean defect over time, one of the analyses used in this study, is not generally considered a reliable measure of glaucomatous progression.
Classification:
9.2.4 Normal pressure glaucoma (Part of: 9 Clinical forms of glaucomas > 9.2 Primary open angle glaucomas)
