David O Zamora1, Jeffrey W Kiel. 1. Department of Ophthalmology, University of Texas Health Science Center, San Antonio, Texas 78229, USA. zamorado@uthscsa.edu
Abstract
PURPOSE: To determine the effect of proparacaine-induced topical anesthesia on episcleral venous pressure (EVP). METHODS: In anesthetized rabbits (n = 11), EVP was measured with a servonull micropressure system, with glass pipettes with 2- to 3-microm tips used to cannulate episcleral veins. Additional measurements included arterial, intraocular, and orbital venous pressures obtained by direct cannulation, to assess the ocular pressure gradients, and carotid blood flow and heart rate, to verify preparation stability. The protocol entailed 5 to 10 minutes of stable baseline recording followed by topical application of proparacaine (0.5%, 10 microL) with continued measurements for another 5 to 15 minutes. RESULTS: Baseline EVP without topical anesthesia was 12.3 +/- 1.1 mm Hg. EVP decreased significantly to 8.7 +/- 0.9 mm Hg within minutes after application of proparacaine. A small decrease also occurred in intraocular pressure. All other measured variables were unchanged. CONCLUSIONS: These results suggest that the episcleral circulation is under tonic neural control and that either an upstream resistance site is under tonic vasodilatory control or a downstream site is under vasoconstrictor control.
PURPOSE: To determine the effect of proparacaine-induced topical anesthesia on episcleral venous pressure (EVP). METHODS: In anesthetized rabbits (n = 11), EVP was measured with a servonull micropressure system, with glass pipettes with 2- to 3-microm tips used to cannulate episcleral veins. Additional measurements included arterial, intraocular, and orbital venous pressures obtained by direct cannulation, to assess the ocular pressure gradients, and carotid blood flow and heart rate, to verify preparation stability. The protocol entailed 5 to 10 minutes of stable baseline recording followed by topical application of proparacaine (0.5%, 10 microL) with continued measurements for another 5 to 15 minutes. RESULTS: Baseline EVP without topical anesthesia was 12.3 +/- 1.1 mm Hg. EVP decreased significantly to 8.7 +/- 0.9 mm Hg within minutes after application of proparacaine. A small decrease also occurred in intraocular pressure. All other measured variables were unchanged. CONCLUSIONS: These results suggest that the episcleral circulation is under tonic neural control and that either an upstream resistance site is under tonic vasodilatory control or a downstream site is under vasoconstrictor control.
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