The influence of intraocular pressure on visual field damage in patients with normal-tension and high-tension glaucoma

There have been several reports to suggest that the type of visual field damage in open-angle glaucoma is influenced by intraocular pressure (IOP). This study was undertaken to determine the extent to which patients with normal-tension (NTG) and high-tension glaucoma (HTG) could be differentiated on the basis of some features of their visual fields. The results from 40 pairs of NTG and HTG patients were matched closely for the extent of visual field damage, pupil size, and visual acuity. Using this pooled material, the authors increased the IOP difference between the two groups in either direction, ie, by either progressively lowering the highest recorded IOP allowed for inclusion in the NTG group or by progressively increasing that required for inclusion in the HTG group. They compared the normal areas of the patients' visual fields by using simple visual field indices designed to quantify the undisturbed field. Using receiver operating characteristics (ROC) analysis, they showed that changing the inclusion criterion in the NTG group resulted in no better separation between the groups. However, when the inclusion criterion was changed in the HTG group, the two groups tended to become more separable. In this case, the degree of separation appeared to be related to the difference in the highest recorded IOP between the two groups although the separation was not complete. These findings show that pressure has a greater influence on the type of visual field damage at the higher end of the IOP spectrum encountered in open-angle glaucoma and suggest that there is no common single pathophysiologic mechanism in this disease.