The visual response to increased ocular blood flow in normal pressure glaucoma

The vascular reactivity to breathing carbon dioxide represents a widely used method in neurology to diagnose microvascular cerebral disorders. Fifteen eyes of 15 patients suffering from confirmed normal pressure glaucoma were included in the study. The ocular carbon dioxide reactivity was determined by recording ocular pulse amplitudes (OPA) by means of oculo-oscillo-dynamography (OODG). The initial pulse amplitudes were found to be comparable to healthy subjects. According to the results obtained during breathing increased carbon dioxide concentrations (95% O2; 5% CO2; endtidal CO2 approx. 6.5%), the collective of 15 patients could be subdivided into two subgroups. One group (n = 9) showed a carbon dioxide reactivity that was comparable to healthy subjects, i.e., an increase of ocular pulse amplitudes of 57%. The remaining six eyes, however, showed a statistically significantly higher OPA increase compared to the first subgroup. According to the results obtained and to evaluate the hypothesis that these hemodynamic changes are accompanied by functional improvements, central visual fields were performed during breathing room air or increased inspiratory carbon dioxide concentrations. After exposure to carbon dioxide the visual fields improved significantly in patients who showed a significant increase in OPA. An increased carbon dioxide reactivity in some normal pressure glaucoma patients, i.e., a significant increase of OPA and a significant improvement of the central visual field during exposure to increased inspiratory carbon dioxide concentrations, may be due to an initial ocular vasospasm in these patients, which can be released by induced vasodilation due to carbon dioxide exposure.