Method Article

Fundus Photography as a Convenient Tool to Study Microvascular Responses to Cardiovascular Disease Risk Factors in Epidemiological Studies

DOI:

10.3791/51904

⸱

October 22nd, 2014

 ,  ,  ,  , 
1Environmental Risk and Health, Flemish Institute for Technological Research (VITO), 2Centre for Environmental Sciences, Hasselt University, 3Transportation Research Institute, Hasselt University, 4Department of Public Health, Occupational and Environmental Medicine, Leuven University

In This Article

Summary

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Retinal image analysis is an unobtrusive procedure for visualizing the microcirculation. The impact of cardiovascular disease risk factors can result in changes of retinal vessel calibers. The procedures to acquire fundus images and the steps for calculating the vessel calibers are described.

Abstract

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The microcirculation consists of blood vessels with diameters less than 150 µm. It makes up a large part of the circulatory system and plays an important role in maintaining cardiovascular health. The retina is a tissue that lines the interior of the eye and it is the only tissue that allows for a non-invasive analysis of the microvasculature. Nowadays, high-quality fundus images can be acquired using digital cameras. Retinal images can be collected in 5 min or less, even without dilatation of the pupils. This unobtrusive and fast procedure for visualizing the microcirculation is attractive to apply in epidemiological studies and to monitor cardiovascular health from early age up to old age.

Systemic diseases that affect the circulation can result in progressive morphological changes in the retinal vasculature. For example, changes in the vessel calibers of retinal arteries and veins have been associated with hypertension, atherosclerosis, and increased risk of stroke and myocardial infarction. The vessel widths are derived using image analysis software and the width of the six largest arteries and veins are summarized in the Central Retinal Arteriolar Equivalent (CRAE) and the Central Retinal Venular Equivalent (CRVE). The latter features have been shown useful to study the impact of modifiable lifestyle and environmental cardiovascular disease risk factors.

The procedures to acquire fundus images and the analysis steps to obtain CRAE and CRVE are described. Coefficients of variation of repeated measures of CRAE and CRVE are less than 2% and within-rater reliability is very high. Using a panel study, the rapid response of the retinal vessel calibers to short-term changes in particulate air pollution, a known risk factor for cardiovascular mortality and morbidity, is reported. In conclusion, retinal imaging is proposed as a convenient and instrumental tool for epidemiological studies to study microvascular responses to cardiovascular disease risk factors.

Introduction

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The microcirculation consists of blood vessels with diameters less than 150 µm and includes smallest resistance arteries, arterioles, capillaries, and venules. These vessels make up a large part of the circulatory system and play an important role in maintaining cardiovascular health. The vessel diameter of 150 µm is a physiological and a physical limit. The rheological properties of vessels with a diameter less than 150 µm differ from large arteries. Furthermore, most of the autoregulatory resistance changes occur downstream from 150 µm in vascular beds exhibiting blood flow autoregulation1. The microcirculation has two important functi....

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Protocol

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The Ethics Board of Hasselt University and University Hospital Antwerp approved the studies. Participants gave their written informed consent to participate.

1. Instrument Setup

  1. Remove the black protection shells from the digital retinal camera and the main block of the unit.
  2. Open the battery compartment and place the battery in the camera. Do not disconnect the wire connecting the battery and the main unit.
  3. Screw the camera onto the main unit and connect the two wires. Connect the main unit to the power grid and to the computer with the supplied USB cables.
  4. Start the main unit by switching the on/o....

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Results

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Repeatability of CRAE and CRVE Determination

A panel of 61 individuals between 22 to 56 years old and free of clinically diagnosed cardiovascular diseases was recruited for studying technical repeatability and within-rater variability of Central Retinal Arteriolar Equivalent (CRAE) and Central Retinal Venular Equivalent (CRVE) determinations. The fundus of the right eye of each individual was photographed twice within a time period of 5 min using a retinal camera (Figures 1 and <.......

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Discussion

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Retina image analysis is proposed as a convenient tool for studying microvascular responses in epidemiological studies. When the operator is experienced, it takes less than 5 min to take a fundus picture. Furthermore, this unobtrusive procedure for visualizing the microcirculation can be used for participants from early age up to old age.

Literature is increasing with respect to the associations between morphological changes in the retinal vasculature (for example change in vessel ca.......

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Disclosures

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The authors declare they have no actual or potential competing financial interests.

Acknowledgements

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The results about the microvascular response to particulate air pollution are reproduced with permission from Environmental Health Perspectives24. The validated meteorological and air quality data were kindly provided by The Belgian Royal Meteorological Institute and the Flemish Environmental Agency. The retinal image analysis software was obtained from Dr. N. Ferrier (Madison School of Engineering and the Fundus Photograph Reading Center, Department of Ophthalmology and Visual Sciences, University of Wisconsin–Madison). Tijs Louwies and Eline Provost are supported with a VITO fellowship. Eline Provost holds an aspirant research fellowship of the Flem....

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Materials

List of materials used in this article
NameCompanyCatalog NumberComments
Canon CR-2 nonmydriatic retinal camera Hospithera (Brussels, Belgium)http://www.usa.canon.com/cusa/healthcare/products/eyecare/digital_non_mydriatic_retinal_cameras/cr_2. Any other retinal camera with comparable resolution and specifications can be used for the analysis of the retinal microvasculature. Compatibility should  be checked before starting a study.
IVAN: Vessel Measurement SoftwareThis software can be used without charge for scientific purpose. It can be obtained by contacting Dr. Nicola Ferrier (Madison School of Engineering and the Fundus Photograph Reading
Center, Department of Ophthalmology and Visual Sciences, University of Wisconsin–Madison). http://directory.engr.wisc.edu/me/faculty/ferrier_nicola. Phone: (608) 265-8793,
Fax: (608) 265-2316 or e-mail: ferrier@engr.wisc.edu
 

References

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  1. Clough, G., Cracowski, J. L. Spotlight Issue: Microcirculation-From a Clinical Perspective. Microcirculation. 19, 1-4 (2012).
  2. Tsai, A. G., Johnson, P. C., Intaglietta, M. Oxygen gradients in the microcirculation. Physiological Reviews. 83, 933-963 (2003).
  3. Safar,....

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Tags

Fundus PhotographyRetinal ImagingMicrovascular ResponsesCardiovascular EpidemiologyCentral Retinal Arteriolar EquivalentCentral Retinal Venular EquivalentRetinal Vessel AnalysisAir Pollution ExposurePanel Study DesignNon invasive Technique

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