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K. Bang, D.B. Pedersen, J.F. Kiilgaard, T. Eysteinsson, P.K. Jensen, M. la Cour, E. Stefánsson; Optic Nerve Oxygen Tension: The Effect of Timolol and Dorzolamide . Invest. Ophthalmol. Vis. Sci. 2003;44(13):335.
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Purpose: We have previously reported that carbonic anhydrase inhibitors, such as acetazolamide and dorzolamide, raise optic nerve oxygen tension. We investigated whether two other common glaucoma treatments; timolol used alone and dorzolamide and timolol used in combination, have similar effects. Methods: The oxygen tension over the optic nerve (ONPO2) was measured with a polarographic oxygen electrode mounted with an internal Ag/AgCl reference electrode inside a 20-gauge needle (model 768-20R, Diamond General Development Corporation, Ann Arbor, MI, USA). The tip of the electrode was placed in the vitreous humour 0.5 mm above the optic disc in anaesthetized pigs; the treatment of the pigs followed the ARVO resolution for the use of animals in ophthalmic and vision research. ONPO2, arterial blood pressure, heart rate and arterial blood gasses were recorded continuously. In 2 groups of pigs, either 100 mg timolol (Timacar®, MSD Inc.) or a combination of 100 mg timolol and 500 mg dorzolamide HCl (MSD Inc.) was injected intravenously. Results: Baseline ONPO2 (mean ± SD) was 3.95 ± 1.08 kPa (n=9). Administration of 100 mg timolol decreased ONPO2 non-significantly by – 0.13 ± 0.16 kPa after 30 min (n=5, p=0.157). Administration of dorzolamide and timolol simultaneously increased ONPO2 by 0.82 ± 0.21 kPa (n=4, p=0.004). The ONPO2 increase induced by timolol and dorzolamide in combination is not significantly different from the increase caused by dorzolamide alone. Conclusions: Systemic administration of timolol does not affect the optic nerve oxygen tension. Timolol and dorzolamide given simultaneously increases ONPO2 as much as dorzolamide when administered alone.
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