Heidelberg Retinal Flowmetry: The effect of angle of incidence on blood flow measurement

L. E. Kagemann, A. Harris, L. B. Cantor, B. J. Martin

Research output: Contribution to journalArticle

1 Scopus citations


Purpose. Accurate measurement of retinal and optic nerve head blood flow is critical in visual science. The Heidelberg Retinal Flowmeter (HRF) measures volumetric flow in a retinal or nerve head sample volume via infrared laser Doppler spectral analysis of red cell volume and velocity. The laser, however, has only a 10 x 10 micrometer focal point, raising the possibility that insufficient scattering of light in the tissue will bias flow readings in the direction of the incident beam. We tested this hypothesis by comparing flow recordings at the same tissue location using two angles of incidence. Methods. HRF exams were performed on 12 healthy persons (5 males 7 females; average age 31 ± 10) Identical tissue locations, determined using anatomical landmarks, were analyzed using both extreme temporal and extreme nasal illumination. The two angles of incidence differed by 20 ± 2 degrees. Results. Flow indices averaged 569 ± 116 a nasal illumination, and 597 ± 118 at temporal illumination (p=NS) If no scatter existed and all capillaries lay in a single plane, a 35% difference in flow would have been expected from these two incidence angles. Conclusions. HRF recordings are not dependent upon the angle of the incident beam, either because scatter is sufficient to illuminate all vessels at 180 degrees to flow, or because capillary distribution is sufficiently random.

Original languageEnglish (US)
Pages (from-to)S265
JournalInvestigative Ophthalmology and Visual Science
Issue number3
StatePublished - Feb 15 1996

ASJC Scopus subject areas

  • Ophthalmology
  • Sensory Systems
  • Cellular and Molecular Neuroscience

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