Regional distribution of optic nerve head blood flow

Background: Advanced glaucoma typically results in damage of the temporal n euroretinal rim. As vascular factors are of pathogenic importance in the de velopment of glaucomatous damage, the present study investigated whether re gional differences in perfusion might be the reason for the preferential da mage of the temporal neuroretinal rim. Material and methods: Blood flow of the neuroretinal rim was measured with the laser Doppler flowmeter (LDF) Oculix 4000 (continuous measurement of an area of 160 mu m diameter) and the Heidelberg retina flowmeter (HRF). Both instruments measure the capillary blood flow (flow), the relative velocity of erythrocytes (velocity) and the relative volume of moving erythrocytes (volume). We examined one randomly chosen eye of 55 healthy subjects withou t history of glaucoma aged 22-57 years (mean 30 years). Each subject was me asured with the LDF and HRF, each time nasally and temporally, away from vi sible vessels. The intraocular pressure (IOP) was measured with the Goldman n tonometer. Heart rate and systolic and diastolic blood pressure were meas ured. Results: The LDF measurements of the optic nerve head showed nasal flow of 12.4 +/- 5.6 AU and temporal flow of 9.8 +/- 3.6 AU. The HRF showed a nasal flow of 477 +/- 161 AU and a temporal flow of 368 +/- 166 AU. The volume m easurements done by LDF showed nasally a value of 0.68 +/- 0.40 AU and temp orally a value of 0.46 +/- 0.21 AU. The HRF volume measurements showed nasa l values of 16.1 +/- 4.3 AU and temporal values of 13.0 +/- 3.0 AU. The LDF velocity values were nasally 0.22 +/- 0.05 kHz and temporally 0.26 +/- 0.0 5 kHz. HRF measurements showed velocity values of 1.7 +/- 0.5 kHz nasally a nd 1.3 +/- 0.6 kHz temporally. The differences were highly statistically si gnificant for now (LDF P = 0.00007, HRF P = 0.0005), volume (LDF P = 0.0000 2, MRF P = 0.00004) and velocity (LDF P = 0.0002, HRF P = 0.00004). The IOP was 12.6 mmHg. Blood pressure was 118/75 mmHg and the heart rate was 73 be ats per minute. There was no correlation between age, IOP, BP and HR and th e HRF/LDF measurements. Conclusion: The measurements with two different methodologies showed a decr eased blood flow of the temporal neuroretinal rim compared to the nasal sid e. These local differences might be one reason for the preferential damage of the temporal neuroretinal rim in advanced glaucoma.