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Abstract #5326 Published in IGR 1-2

Comparison of glaucomatous progression between untreated patients with normal-tension glaucoma and patients with therapeutically reduced intraocular pressures: the effectiveness of intraocular pressure reduction in the treatment of normal-tension glaucoma

Danias J; Podos SM; Anderson DR; Drance SM; Schulzer M; Leske MC; Hyman L; Hussein M; Heijl A; Bengtsson B
American Journal of Ophthalmology 1999; 127: 623-625


In this letter to the editor, the authors comment on two papers by the collaborative Normal Tension Glaucoma study Group published in October 1998 in the American Journal of Ophthalmology. The corresponding authors agree with the conclusion that patients with normal tension glaucoma treated with an intent to decrease intraocular pressure by 30% derive a significant benefit in terms of disease non-progression compared with non-treated patients. However, they cannot accept the conclusion that intraocular pressure is part of the pathogenesis of normal tension glaucoma. They point out that the results could also be explained in a different way. The reduction in intraocular pressure could either be an integral part of the pathogenesis of glaucoma or just be closely related to these mechanisms without necessarily having a cause and effect relationship. There could be another intermediate factor hitherto unknown. The corresponding authors point out that neither the absolute nor the percentage change in intraocular pressure over the follow-up period show any significant association with survival within either group. They would have expected such a dose-dependent response. The authors feel that there is insufficient information on the number of patients who were treated medically, with ALT, or surgically. They come up with several suggestions for processes other than direct intraocular pressure reduction that could be involved. For instance, they mention that intraocular pressure reduction may cause a significant increase in ocular blood flow. This in turn would give an improvement of perfusion pressure. The corresponding authors feel that their suggestion justifies re-analysis of the data. In their reply, the original authors agree that a correlation between two variables does not establish a cause and effect relationship. As far as the lack of persons of a dose relationship is concerned, they respond that the spread of postoperative intraocular pressure was too small to show an intraocular pressure effect within the treated group alone. In fact, this effect is to be expected if the aim is a pressure lowering of 30%. The study design did not permit analysis of a graded dose effect. However, this does not imply that such an effect does not exist. Even if a dose response relationship exists, this does not prove the cause effect relationship. The number of subjects in each of the treatment subgroups was too small for further analysis. If the 39 subjects who had had medical and laser treatment were compared to the 33 who required filtering surgery, there was no statistical difference in survival time. There seems to be no basis to suspect that treatment mode had any impact on the results. The original authors feel that their findings are consistent with a cause and effect relationship between intraocular pressure and glaucoma damage. They also particularly point to other evidence in this respect.


Classification:

9.2.4 Normal pressure glaucoma (Part of: 9 Clinical forms of glaucomas > 9.2 Primary open angle glaucomas)



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