New observations concerning the nature of central retinal vein pulsation.

AIMS Central retinal vein pulsation is affected by intracranial pressure (ICP), glaucoma and venous pathology. Its genesis is poorly understood with most models suggesting that intraocular pressure (IOP) fluctuation dominates the rhythm of venous pulsation; however, this has not been explored experimentally. This study planned to measure the timing of central retinal vein pulsation with respect to IOP pulse. METHODS Video recording of the optic disc vessels and movement of Goldmann applanation mires while recording the cardiac cycle with a pulse oximeter probe was undertaken in 10 subjects from a general ophthalmic clinic. The timing of the variation in IOP and retinal vein diameter from the onset of the oximeter signal were expressed as a percentage of the cardiac cycle and also in degrees of the cycle. RESULTS Minimum vein diameter occurred at a mean 40 ms (SD 47) after minimum IOP in 10 subjects with mean cardiac cycle length of 866 ms (SD 132), the delay representing 4% or 14 degrees (SD 5.1, 95% CI 0.3% to 8%) of the mean cardiac cycle. Maximum vein diameter occurred an average of 5 ms after maximum IOP (SD 57) representing 1% or 4 degrees (SD 6.9, 95% CI -4% to 6%) of the mean cardiac cycle. CONCLUSION During venous pulsation, venous collapse occurred in time with ocular diastole and dilatation in time with systole. This is contrary to earlier conceptual understanding. The results suggest that the intracranial pulse pressure may be of equal importance to intraocular pulse pressure in producing venous pulsation.