97th DOG Annual Meeting 1999
THE CARBON-DIOXIDE-TEST IN THE DIFFERENTIAL DIAGNOSIS OF NORMAL PRESSURE GLAUCOMA AND ANTERIOR ISCHEMIC OPTIC NEUROPATHY
M. Müller, L. E. Pillunat, A. G. Böhm, A. U. Köller, A. S. Bernd
Purpose: Vascular factors are of pathogenetic importance in normal pressure glaucoma (NPG) and in anterior ischemic optic neuropathy (AION). In AION, however, the pathogenetic origin seems to be arteriosclerotic whereas in NPG there might be some functional (Vasospastic) vascular dysfunction. To prove this hypothesis the effect of provoked vasodilation on the visual field was examined.
Methods: In a clinical study 11 patients with AION (age=68 years, 6 female, 5 male) and 20 patients with NPG (age=62 years, 12 female, 8 male) were included in the study. In bilateral NPG 1 eye was chosen by random. For a provoked vasodilation the carbogen-test (95% O2 and 5% CO2 in a partly closed rebreathing system) was used during visual field testing (Humphrey 30-2 visual field). The visual field was performed under room air condition or under carbogen condition in a randomly choosen sequence. A change of the visual field exceeding the actual short time fluctuation was regarded as a positive response to provoked vasodilation. For statistical analysis the Mann-Whitney-U-Test was used.
Results: The visual field of 7 patients with NPG improved significantly (p<0,01) during carbogen-breathing (MD-Baseline:-12,49 dB; MD-Carbogen: -4,02 dB). In 13 patients, however, there was no significant decrease of visual field (MD-Baseline: 13,58 dB; MD-Carbogen:-13,49 dB). All patients suffering from AION, however, showed a significant decrease of visual function (p<0,01). The mean deviation at baseline (room air) was found to be -12,88 dB and under carbogen-condition it was found to be -16,84 dB.
Conclusion: The results presented show that a subgroup of NPG patients suffer from a functional vascular disorder which is released by exposure to vasodilators. The majority of NPG patients, however, did not show any changes. In AION, however, a provoked vasodilation leads possibly to a steel effect in the small vasculature which leads to a worsening of visual function. Therefore a vasodilatory therapy in AION seems not to be advisable.
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