SCIENTIFIC REPORT

The effect of image alignment on capillary blood flow measurement of the neuroretinal rim using the Heidelberg retina flowmeter

M Sehi and J G Flanagan

School of Optometry University of Waterloo, Waterloo, ON, Canada N2L 3G1

Correspondence to:
Correspondence to:
Dr Mitra Sehi
School of Optometry University of Waterloo, Waterloo, ON, Canada N2L 3G1; msehizad{at}sciborg.uwaterloo.ca

Aim: To examine the influence of image alignment on the repeatability of blood flow measurements of the optic nerve.

Methods: 10 normal subjects were examined. Heidelberg retina tomograph imaging was performed to establish best location and focus for the temporal neuroretinal rim. Two high quality Heidelberg retina flowmeter (HRF) images were acquired for three methods of alignment: central, nasal, and temporal. A 10x10 pixel measurement window was selected and exactly reproduced on all images. The interquartile pixel values were used to calculate capillary flow. ANOVA, intraclass correlation coefficients (ICC) and the coefficient of repeatability (CoR) were used for analysis.

Results: There was no difference between methods (p = 0.47) or between visits (p = 0.51). The ICCs were 0.83 for the central, 0.34 for the nasal, and 0.42 for the temporal alignment. The CoR was 31.5 for central (mean effect 235.1), 234.6 for nasal, and 256.7 for temporal alignment.

Conclusion: Central alignment was the most repeatable method for the measurement of neuroretinal rim capillary blood flow using the HRF.

Keywords: Heidelberg retina flowmetery; ocular blood flow; laser Doppler flowmetry; optic nerve imaging; scanning laser tomography

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