March 1999
Volume 40, Issue 3
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Articles  |   March 1999
Brightness alters Heidelberg retinal flowmeter measurements in an in vitro model.
Author Affiliations
  • A C Tsang
    Department of Ophthalmology, Indiana University School of Medicine, Indianapolis 46202, USA.
  • A Harris
    Department of Ophthalmology, Indiana University School of Medicine, Indianapolis 46202, USA.
  • L Kagemann
    Department of Ophthalmology, Indiana University School of Medicine, Indianapolis 46202, USA.
  • H S Chung
    Department of Ophthalmology, Indiana University School of Medicine, Indianapolis 46202, USA.
  • B M Snook
    Department of Ophthalmology, Indiana University School of Medicine, Indianapolis 46202, USA.
  • H J Garzozi
    Department of Ophthalmology, Indiana University School of Medicine, Indianapolis 46202, USA.
Investigative Ophthalmology & Visual Science March 1999, Vol.40, 795-799. doi:
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    • Get Citation

      A C Tsang, A Harris, L Kagemann, H S Chung, B M Snook, H J Garzozi; Brightness alters Heidelberg retinal flowmeter measurements in an in vitro model.. Invest. Ophthalmol. Vis. Sci. 1999;40(3):795-799.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

PURPOSE: The Heidelberg Retinal Flowmeter (HRF), a laser Doppler flowmetry device, has captured interest as a research and clinical tool for measurement of ocular blood flow. Concerns remain about the range and accuracy of the values that it reports. METHODS: An in vitro blood-flow model was constructed to provide well-controlled laminar flow through a glass capillary for assessment by HRF. A change in material behind the glass capillary was used to simulate changing brightness conditions between eyes. RESULTS: Velocities reported by the HRF correlated linearly to true velocities below 8.8 mm/sec. Beyond 8.8 mm/sec, HRF readings fluctuated randomly. True velocity and HRF reported velocities were highly correlated, with r = 0.967 (P < 0.001) from 0.0 mm/sec to 2.7 mm/sec mean velocity using a light background, and r = 0.900 (P < 0.001) from 2.7 mm/sec to 8.8 mm/sec using a darker background. However, a large change in the y-intercept occurred in the calibration curve with the background change. CONCLUSIONS: The HRF may report velocities inaccurately because of varying brightness in the fundus. In the present experiment, a darker background produced an overreporting of velocities. An offset, possibly introduced by a noise correction routine, apparently contributed to the inaccuracies of the HRF measurements. Such offsets vary with local and global brightness. Therefore, HRF measurements may be error prone when comparing eyes. When used to track perfusion in a single eye over time, meaningful comparison may be possible if meticulous care is taken to align vessels and intensity controls to achieve a similar level of noise correction between measurements.

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