April 2010
Volume 51, Issue 13
Free
ARVO Annual Meeting Abstract  |   April 2010
Suboptimal Image Focus Broadens Retinal Vessel Caliber Measurements
Author Affiliations & Notes
  • C. S. Chandler
    Ophthalmology, Fundus Photograph Reading Center, Madison, Wisconsin
  • L. D. Hubbard
    Ophthalmology, Fundus Photograph Reading Center, Madison, Wisconsin
  • N. J. Ferrier
    School of Engineering, University of Wisconsin, Madison, Wisconsin
  • S. Gangaputra
    Ophthalmology, Fundus Photograph Reading Center, Madison, Wisconsin
  • T. W. Pauli
    Ophthalmology, Fundus Photograph Reading Center, Madison, Wisconsin
  • Q. Peng
    Ophthalmology, Fundus Photograph Reading Center, Madison, Wisconsin
  • R. P. Danis, Jr.
    Ophthalmology, Fundus Photograph Reading Center, Madison, Wisconsin
  • Footnotes
    Commercial Relationships  C.S. Chandler, None; L.D. Hubbard, None; N.J. Ferrier, None; S. Gangaputra, None; T.W. Pauli, None; Q. Peng, None; R.P. Danis, Jr., None.
  • Footnotes
    Support  Unrestricted grant from research to prevent blindness
Investigative Ophthalmology & Visual Science April 2010, Vol.51, 2276. doi:https://doi.org/
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    • Get Citation

      C. S. Chandler, L. D. Hubbard, N. J. Ferrier, S. Gangaputra, T. W. Pauli, Q. Peng, R. P. Danis, Jr.; Suboptimal Image Focus Broadens Retinal Vessel Caliber Measurements. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2276. doi: https://doi.org/.

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

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Abstract

Purpose: : To determine the extent to which suboptimal image focus might skew measurement of retinal vessel caliber. Studies have utilized central retinal arteriolar and venular calibers (CRAE & CRVE), measured from images using IVAN software (UW-Madison), to detect risk factors for systemic diseases. Rochtchina et al. (2008) found systematic differences in caliber between racial groups: in eyes with greater pigmentation, measured CRAE & CRVE are greater, even after adjustment for other factors. One hypothesis is that this is due to racial difference in RPE/blood vessel contrast and/or suboptimal focus rather than an anatomic variation. We explored differential image focus as a possible contributing factor to larger vascular caliber measurements in eyes with greater RPE pigmentation.

Methods: : From the reading center database, 20 digital retinal images were selected for optimum quality (focus, illumination) - 10 from Caucasians and 10 from African Americans (judging from skin/iris pigmentation in anterior images). Adobe Photoshop CS3 (Box Blur) was used to derive 9 progressively more blurred versions of the originals - all still within the normal focus range observed at our reading center. IVAN (v1.3) was used to measure CRAE & CRVE in the originals and their blurred series.

Results: : Median CRAE = 154µm and CRVE = 237µm across groups. Comparing CRAE and CRVE between blurred variants and original images with the Wilcoxon signed rank test we found significant difference (p<0.01) in caliber at all blur levels in both racial groups (except Blur 1/Caucasian, P=0.05). Measured vascular caliber increased at higher blur levels. CRAE exceeded a threshold of +5µm at Blur 3-4 and CRVE at Blur5, and approached +20µm at Blur7 for both vessel types.

Conclusions: : Suboptimal image focus artificially broadens measured vessel caliber - regardless of racial group. Differences reported by Rochtchina were CRAE - 11µm, CRVE - 18µm. If there are systematic reasons for more suboptimal focus in some racial groups (darker/lower contrast images are harder to focus), this effect may contribute to racial differences in vessel measurement.

Keywords: clinical (human) or epidemiologic studies: biostatistics/epidemiology methodology • imaging/image analysis: clinical • retina 
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