[Effects of intraocular pressure on the optic nerve head in albino rabbits]

The effects of intraocular pressure (IOP) on the blood flow in the laminar portion of the optic nerve head in adult albino rabbits were investigated employing the hydrogen clearance method. The blood flow volume at the normal IOP level of 15 mmHg was 119.0 +/- 25.0 ml/min/100 g (mean +/- S.D.). When the IOP was raised every 30 minutes from 5 mmHg to 15, 25, 35, 45 and 55 mmHg in a stepwise fashion, the mean blood flow volume at 5 mmHg was almost the same as the volume at 15 mmHg, but a significant linear decrease was observed at 35 mmHg or more. The decreased blood flow returned to the initial level when the raised IOP was restored to normal. When the IOP was raised to 55 mmHg, the optic nerve potential (ONP) amplitude decreased and the peak latency became gradually prolonged with time, and finally the ONP became almost impossible to measure after 30 minutes, before remarkable changes were noted on the electroretinogram. However, quick recovery of the ONP was recognized within 5 minutes after returning to a normal IOP level of 15 mmHg. These findings indicate that vascular changes might have an important effect on the optic nerve head function or action potential.