June 2015
Volume 56, Issue 7
Free
ARVO Annual Meeting Abstract  |   June 2015
Image Quality Affects Measurements of Retinal Vessel Oxygen Saturation
Author Affiliations & Notes
  • Sveinn Hakon Hardarson
    Ophthalmology, University of Iceland / Landspítali University Hospital, Reykjavik, Iceland
  • Benedikt Atli Jonsson
    Electrical- and Computer Engineering, University of Iceland, Reykjavik, Iceland
  • Robert Arnar Karlsson
    Oxymap ehf., Reykjavik, Iceland
  • Asbjorg Geirsdottir
    St. Eriks Eye Hospital, Stockholm, Sweden
  • David Bragason
    Ophthalmology, University of Iceland / Landspítali University Hospital, Reykjavik, Iceland
  • Thor Eysteinsson
    Ophthalmology, University of Iceland / Landspítali University Hospital, Reykjavik, Iceland
    Physiology, University of Iceland, Reykjavik, Iceland
  • Olof Birna Olafsdottir
    Ophthalmology, University of Iceland / Landspítali University Hospital, Reykjavik, Iceland
  • Jona Valgerdur Kristjansdottir
    Ophthalmology, University of Iceland / Landspítali University Hospital, Reykjavik, Iceland
  • Einar Stefansson
    Ophthalmology, University of Iceland / Landspítali University Hospital, Reykjavik, Iceland
  • Footnotes
    Commercial Relationships Sveinn Hardarson, Oxymap ehf. (C), Oxymap ehf. (I), Oxymap ehf. (P); Benedikt Jonsson, Oxymap ehf. (F); Robert Karlsson, Oxymap ehf. (E), Oxymap ehf. (I), Oxymap ehf. (P); Asbjorg Geirsdottir, None; David Bragason, None; Thor Eysteinsson, Oxymap ehf. (I), Oxymap ehf. (P); Olof Olafsdottir, None; Jona Kristjansdottir, None; Einar Stefansson, Oxymap ehf. (I), Oxymap ehf. (P), Oxymap ehf. (S)
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2015, Vol.56, 3316. doi:
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      Sveinn Hakon Hardarson, Benedikt Atli Jonsson, Robert Arnar Karlsson, Asbjorg Geirsdottir, David Bragason, Thor Eysteinsson, Olof Birna Olafsdottir, Jona Valgerdur Kristjansdottir, Einar Stefansson; Image Quality Affects Measurements of Retinal Vessel Oxygen Saturation. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3316.

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

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Abstract
 
Purpose
 

Non-invasive measurements of oxygen saturation in retinal vessels are based on retinal images, taken at two wavelengths of light. The purpose of the study was to test if and how image quality affects measurements of retinal vessel oxygen saturation.

 
Methods
 

The retinal oximeter (Oxymap ehf., Iceland) simultaneously acquires images of the retina at 570nm and 600nm. Software automatically measures light absorbance of retinal vessels and calculates oxygen saturation. A newly developed software tool automatically grades the images on the scale of 0 to 1 according to quality of the images. The quality grade is composed of assessment of focus and contrast. Oximetry images of 108 healthy individuals (age 18-77) and 17 individuals, scheduled for cataract surgery were analyzed for quality.

 
Results
 

In the heatlhy individuals, measured venous oxygen saturation decreased with worsening image quality (p<0.0001, R2=0.17) but measured arteriolar oxygen saturation was not significantly affected (p=0.79). A linear model indicated that the relationship between quality and measured venous saturation was not due to age: VenousSaturation=26-0.043*Age+37*ImageQualityGrade, p=0.29 for age and p=0.0008 for image quality. Further analysis showed that the effect of image quality was due to contrast (p=0.0002) rather than focus (p=0.36). In individuals scheduled for cataract surgery, image quality correlated positively with measured oxygen saturation in both arterioles (p=0.0079, R2=0.38) and venules (p=0.0034, R2=0.45).

 
Conclusions
 

Poor image quality leads to lower measured venous oxygen saturation and, in more extreme cases, also affects measurements of arterioles. This may explain why measured oxygen saturation has previously been found to decrease with age. The new tool for image quality assessment allows quality control of retinal oximetry measurements and may potentially be used to apply correction factors.  

 
The figure shows that measured retinal venous oxygen saturation increases with improved image quality as assessed by an automatic image quality tool. The results of simple linear regression are shown (not corrected for age).
 
The figure shows that measured retinal venous oxygen saturation increases with improved image quality as assessed by an automatic image quality tool. The results of simple linear regression are shown (not corrected for age).

 
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