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Impressum
Topical carbonic anhydrase inhibition and its effect on the autoregulatory capacity of optic nerve head blood flow
Bernd A. S., Pillunat L. E., Boehm A. G., Müller M. F., Mollenhauer K., Feucht M.
Klinik und Poliklinik für Augenheilkunde, Universitätsklinikum Carl Gustav Carus, Dresden
Purpose: In healthy subjects, autoregulatory mechanisms maintain
blood flow relatively constant in the vascular beds of the retina and
the optic nerve head. Aim of the present study was to evaluate the influence
of increased intraocular pressure and the modulating effect of topical
carbonic anhydrase inhibition on the capillary optic nerve head perfusion.
Methods: Laser Doppler flowmetry according to Riva was used to
determine the mean velocity, the number of moving erythrocytes, and the
volume of flow in the capillary bed of the optic disc. These parameters
were measured in 10 healthy subjects ( 3 female, 7 male, mean age 29 years)
at spontaneous levels of intraocular pressure (IOP), and at pressures
artificially elevated to 25, 35, 45 and 55 mmHg with a scleral suction
cup. The measurements were taken at the temporal neuroretinal rim of the
disc. Addtionally intraocular pressure, heart rate and blood pressure
were monitored. All subjects received a treatment with dorzolamide, a
topical carbonic anhydrase inhibitor three times daily for one week. Then
the measurements were repeated. For statistical analysis the Wilcoxon
matched paired test was used (p=0.05).
Results: Intraocular pressure dropped from 14mmHg to 13 mmHg. Systolic
and diastolic blood pressure did not change significantly. The parameter
velocity showed a decrease during IOP elevation with and without treatment
which was statistically significant at an IOP of 45 mmHg. (no treatment:
0,453AU / 0,442AU / 0,411AU / 0,411AU / 0,372AU; dorzolamide: 0,451 /
0,457 / 0,402 / 0,382 / 0,353). The parameter volume increased statistically
not significant under both conditions (no treatment: 0,152AU / 0,16AU
/ 0,183AU / 0,206AU / 0,223AU; dorzolamide: 0,19AU / 0,186AU / 0,219AU
/ 0,226AU / 0,18AU). The parameter flow showed no significant change until
IOP of 45 mmHg without treatment (no treatment: 6,342AU / 6,322AU / 7,118AU
/ 6,325AU / 5,754AU; resp. normalized to baseline 100% / 100% / 112% /
100% / 91%), but a slight statistically not significant increase at IOP
of 25 mmHg (dorzolamide: 6,96AU / 7,516AU / 7,705AU / 7,166AU / 5,593AU;
normalized to baseline 100% / 108% / 111% / 103% / 80%).
Conclusion: The results show that optic nerve head capillary blood
flow is mantained during elevated IOP until 45 mmHg in healthy subjects.
However, optic nerve head blood flow seems to improve at lower IOP of
25 mmHg during dorzolamide treatment. This effect might be due to an enhanced
autoregulatory capacity of optic nerve head blood flow induced by carbonic
anhydrase inhibition.