Modulation of Heidelberg Retinal Flowmeter parameter flow at the papilla of healthy subjects: Effect of carbogen, oxygen, high intraocular pressure, and beta-blockers

The Heidelberg Retina Flowmeter (HRF) is intended to assess ocular blood fl ow by scanning laser doppler flowmetry. In the retina and possibly in the o ptic nerve head, carbogen increases blood flow, whereas pure oxygen or high intraocular pressure (IOP) decrease it. This study addresses whether at th e papilla of healthy volunteers, the HRF parameter flow, is modulated by br eathing 5 % carbogen (5 % carbon dioxide + 95 % oxygen) for 7 minutes, brea thing 100 % oxygen for 7 minutes, increasing IOP to 50 mm Hg with a suction cup, or decreasing IOP with a single topical ocular instillation of the P- blockers 0.5 % betaxolol (betoptic) or 0.5 % timolol (timoptic). At the pap illa (20 degrees X 5 degrees, 256 X 64 pixels), values of HRF parameter, fl ow (50 X 50) pixels, increased after carbogen (N = 5, P < 0.05), but decrea sed after oxygen (N = 5, P < 0.05) or IOP increase (N = 5, P < 0.01). Altho ugh IOP values were significantly reduced by betaxolol (N = 9, P < 0.05) an d timolol (N = 9, P < 0.01), HRF values were only significantly decreased ( N = 9, P < 0.05) after timolol. In conclusion, at the papilla of healthy vo lunteers, a positive correlation exists between changes in values of the HR F parameter, flow, and stimuli considered to modulate retinal and ONH blood flow. Furthermore, although of unknown clinical relevance, it appears that in contrast to betaxolol, values of the HRF parameter, flow, at the papill a of healthy volunteers are significantly decreased after a single instilla tion of timolol. (C) 1999 by Elsevier Science Inc. All rights reserved.