April 2014
Volume 55, Issue 13
Free
ARVO Annual Meeting Abstract  |   April 2014
Retina Artery to Vein Intensity Ratio as a Function of Wavelength and Dark-Field Offset With Low Cost Ophthalmoscope
Author Affiliations & Notes
  • Jason J.A. Green
    Indiana University, Bloomington, IN
  • Ann E Elsner
    Indiana University, Bloomington, IN
    Aeon Imaging, LLC, Bloomington, IN
  • Karthikeyan Baskaran
    Indiana University, Bloomington, IN
  • Bryan P Haggerty
    Indiana University, Bloomington, IN
  • Jeff Clendenon
    Aeon Imaging, LLC, Bloomington, IN
  • Matthew S Muller
    Aeon Imaging, LLC, Bloomington, IN
  • Footnotes
    Commercial Relationships Jason Green, Indiana University (E); Ann Elsner, Aeon Imaging (E), Aeon Imaging (F), Indiana University (E); Karthikeyan Baskaran, Indiana University (E); Bryan Haggerty, Indiana University (E); Jeff Clendenon, Aeon Imaging, LLC (E); Matthew Muller, Aeon Imaging (F), Aeon Imaging (I), Aeon Imaging (P)
  • Footnotes
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Investigative Ophthalmology & Visual Science April 2014, Vol.55, 4328. doi:
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    • Get Citation

      Jason J.A. Green, Ann E Elsner, Karthikeyan Baskaran, Bryan P Haggerty, Jeff Clendenon, Matthew S Muller; Retina Artery to Vein Intensity Ratio as a Function of Wavelength and Dark-Field Offset With Low Cost Ophthalmoscope. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4328.

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

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Abstract
 
Purpose
 

To quantify light return from retinal vessels for oxygenation status. To use a low-cost Digital Light Ophthalmoscope (DLO) based on a novel structured light pattern Digital Light Projector for quantitative retinal imaging.

 
Methods
 

Five normal subjects of ages 27-63 and various eye colors were imaged without mydriasis. The DLO produced a progressively scanning 6 pixel wide stripe, 96 stripe illumination pattern (85 μm stripe width at retina) with LEDs at 635 +/- 25nm (Red) and 535 +/- 70nm (Green) with a constant fixation target location across tests. The illumination was synchronized to a 13.2 Hz rolling shutter CMOS sensor (11 μm resolution at retina). To collect the light return from the retina at varying light multiply scattered levels, aperture offset was varied in position with respect to the illumination centerline: dark-field mode was obtained with large offsets and confocal mode had small offsets, where offset was varied from -517 μm (row start 30) to 1353 μm (row start 200). Multiple images of 12 bit dynamic range were captured in sequence, aligned with translational cross correlation, then time averaged to reduce noise. The artery and vein gray scale intensity level was measured at vessel centers for: 1) both vessels over background retina and 2) artery over the optic disc and vein over background. Mean-to-mean intensity ratios were then compared.

 
Results
 

With an aperture width of 704 μm, intensity varied by 2.60 bits (a factor of 4.5) for each subject per condition: red, green, artery, and vein, 3.39 bits if same subject and condition (2.3% Red A/V ratio CoV σ/μ), and by 5.07 bits over all tests. Yet, the ratio (Red/Green Artery)/(Red/Green Vein) was close to unity across offsets and linear fits had an R^2 regression of, for case 1: 0.72, 0.06, 0.25, 0.18, and 0.49, and case 2: 0.0005, 0.89, 0.75, 0.50, and 0.18. The Artery/Vein ratio trend slopes, intercept points, and inversions varied between subjects, i.e. contrast reversals were observed.

 
Conclusions
 

The DLO can be utilized electronically to effectively perform quantitative fundus imaging at both Red and Green wavelengths, which is a step towards performing oximetry.

 
 
77 is zero offset
 
77 is zero offset
   
Keywords: 688 retina • 551 imaging/image analysis: non-clinical  
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