EFFECT OF BREATHING 100-PERCENT OXYGEN ON RETINAL AND OPTIC-NERVE HEAD CAPILLARY BLOOD-FLOW IN SMOKERS AND NONSMOKERS

Aim - The effect of breathing 100% oxygen on retinal and optic nerve h ead capillary blood flow in smokers and non-smokers was investigated u sing scanning laser Doppler flowmetry (SLDF) as a new non-invasive met hod to visualise and quantify ocular blood flow. Method - 10 eyes of 1 0 young healthy nonsmoking volunteers (mean age 26 (SD 3) years) and n ine eyes of nine young healthy smoking volunteers (mean age 26 (4) yea rs) were investigated. All participants were asked not to smoke or con sume caffeine containing drinks for at least 4 hours before the measur ements. Blood flow measurements were performed before and after 100% o xygen was applied to the subjects through a mask over a period of 5 mi nutes (6 litres per minute). Juxtapapillary retinal and optic nerve he ad blood flow were determined in arbitrary units using SLDF representi ng a combination of laser Doppler flowmetry and a scanning laser syste m allowing visualisation and quantification of the retinal and optic n erve head blood flow. flood flow was determined in an area of 100 mu m x 100 mu m. The level of carboxyhaemoglobin was determined in all sub jects. A Wilcoxon matched pairs signed ranks test (non-parametric) was used for statistical evaluation. Results - In the non-smoking group, retinal 'flow' was reduced by 33% (p = 0.005), optic nerve head 'flow' by 37% (p = 0.005). In the smoking group retinal how was reduced by 1 0% (p = 0.01), optic nerve head how by 13% (p < 0.008). The difference in reactivity to oxygen breathing between smokers and non-smokers was highly significant (p < 0.00001). increased carboxyhaemoglobin levels were not found in either of the groups. A significant reduction of th e mean arterial blood pressure of 6% (5%) (p < 0.02) was observed in t he non-smoking group after administration of oxygen. Conclusion - Thes e results indicate that hyperoxia leads to a decrease in capillary blo od flow of the retina and optic nerve head secondary to vasoconstricti on, and that smokers do not respond to oxygen breathing as non-smokers do. The findings might be based on factors such as long term effects of nicotine on the sympathetic and parasympathetic nervous system.