[The blood flow in post-laminar optic nerve in monkeys was dependent on intraocular pressure level]

The effects of artificial elevation of intraocular pressure on the blood flow in the 1mm post-laminar portion of the optic nerve was evaluated in 9 monkeys (Macaca fuscata). The intraocular pressure of one eye was elevated while the fellow eye served as control. The intraocular pressure of the control was maintained at 15 mmHg. We used the hydrogen clearance method in quantitating the blood flow. Anesthesia was maintained with injection of pentobarbital sodium into the femoral vein. In each experiment, the intraocular pressure was raised from 15 mmHg to 30, 50 or 70 mmHg in a stepwise fashion. At the intraocular pressure level of 15 mmHg, the blood flow measured 120.0 +/- 19.4 ml/min/100g (mean +/- standard deviation). The blood flow decreased linearly along with the rise of intraocular pressure up to 70 mmHg. The blood flow at 70 mmHg was 37% of the initial value. At each level of raised intraocular pressure, the blood flow remained constant for at least 60 minutes. The decreased blood flow promptly returned to the initial level when the raised intraocular pressure was restored to the initial value of 15 mmHg. We concluded from the above findings that the blood flow in the immediate post-laminar portion of the optic nerve is dependent on the level of intraocular pressure up to 70 mmHg.