A pilot study of in vivo venous pressures in the pig retinal circulation

Retinal venous pressure was examined in six pigs using a balanced servo-nul ling micropuncture technique. The mean transmural venous pressure was 0.95 mmHg (SD 1.50 mmHg). The transmural venous pressure was lower at the optic disc than away from the disc (0.32 +/- 1.46 mmHg vs 1.69 +/- 1.19 mmHg, P < 0.01). At the disc a transmural pressure of zero or less (0 to -0.5 mmHg) was demonstrated in 10/21 (48%) of the disc readings. Over an intraocular p ressure range of 15-26 mmHg there was a strong correlation between intraocu lar pressure and retinal venous pressure (Pearson coefficient r = 0.92). Th e results are compatible with the Starling resistor theory of venous outflo w from the eye.