regulation of optic nerve head blood flow in normal tension glaucoma patients purpose to investigate the regulation of the optic nerve blood flow fonh in response to an increase of the perfusion pressure ppm in normal tension glaucoma ntg patients and in agematched normal volunteersmethods measurements were performed in 16 eyes of ntg patients and in 10 eyes of agematched controls laser doppler flowmetry ldf was applied to calculate the relative flux of red blood cells at the temporal rim of the optic nerve head onh in response to increases in ppm ppm was raised through an increase in systemic blood pressure induced by isometric exercise before being tested all patients had 3 weeks of washout of any local medicationresults in the ntg group mean ophthalmic arterial blood pressure increased during isometric exercise from 73 to 89 mmhg 22 resulting in a 29 increase of the ppm this increase did not induce any significant change in mean fonh for the control group the 28 increase of ppm also did not significantly affect fonh there was a trend for a greater increase in vascular resistance during isometric exercise in the ntg than in the normal control group 47 versus 25conclusions the ldf parameters measured in the onh did not indicate an abnormal fonh regulation in response to an increase of the ppm in either normal subjects or ntg patients the maintenance of constant blood flow is achieved by an increase in local vascular resistance our data show a greater percent increase in vascular resistance in the ntg patients compared to the normal subjects for a similar percent increase in ppm in both groups during squatting this suggests some alteration of the vessel tone regulatory mechanisms in ntg patients