Name: fundus photography as a convenient tool to study microvascular responses to cardiovascular disease risk factors in epidemiological studies
Uploaded: 2014-10-22T13:00:00
Description: Watch this Scientific Journal Video about Fundus Photography as a Convenient Tool to Study Microvascular Responses to Cardiovascular Disease Risk Factors in Epidemiological Studies at JoVE.com

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&#8211;Madison). Tijs Louwies and Eline Provost are supported with a VITO fellowship. Eline Provost holds an aspirant research fellowship of the Flemish Scientific Fund. Tim S. Nawrot is holder of a European Research Council starting grant.

The Ethics Board of Hasselt University and University Hospital Antwerp approved the studies. Participants gave their written informed consent to participate.
1. Instrument Setup
<ol>
	<li>Remove the black protection shells from the digital retinal camera and the main block of the unit.</li>
	<li>Open the battery compartment and place the battery in the camera. Do not disconnect the wire connecting the battery and the main unit.</li>
	<li>Screw the camera onto the main unit and connect the tw...

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&#160;min&#160;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...

The microcirculation consists of blood vessels with diameters less than 150 &#181;m 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 &#181;m is a physiological and a physical limit. The rheological properties of vessels with a diameter less than 150 &#181;m differ from large arteries. Furthermore, most of the autoregulatory resistance changes occur downstream from 150 &#181;m in vascular beds exhibiting blood flow autoregulation1. The microcirculation has two important functions. The primary function is to provide cells with oxygen and metabolic substrates in order to match tissue demand and to drain waste products and carbon dioxide. Alterations in the number of exchange vessels and the microvascular flow patterns reduces the effective exchange surface area and may lead to suboptimal tissue perfusion and a failure to meet metabolic demand2. Further, the hydrostatic pressure drops within the vascular bed and the microcirculation plays a role in regulating the overall peripheral resistance3.
The retina is a layered tissue lining the interior of the eye. Its main function is to convert the incoming light into a neural signal that is further propagated to the visual cortex for processing visual information. The function of the retina is to see the outside world and all the ocular structures involved in this process are optically transparent. This makes the retinal tissue accessible for non-invasive imaging of the microvasculature4. Retinal imaging is being used to identify diseases of the eye. For example, an advanced form of macular degeneration can lead to vision loss because of abnormal blood vessel growth into the macula. These blood vessels tend to be more permeable and subject to bleeding and leaking of blood and proteins within or below the retina. The latter events are responsible for the irreversible damage to the photoreceptors. Development of glaucoma correlates with a damaging of ganglion cells and their axons. The effect of this process leads to cupping of the optic disc, which can be observed in retinal images5. Diabetic retinopathy is caused by hyperglycemia that leads to damage in&#160;the retinal vessel walls. This can result in ischemia, the growth of new blood vessels and a change in the vascular geometric network. Furthermore, the blood-retinal barrier may be subject to breakdown, causing leakage of dilated hyperpermeable capillaries and aneurysms6.
Retinal microvasculature shows homology with the microvascular beds found in the heart, lungs, and brain7. It is established that systemic diseases that affect the microcirculation of the brain can cause parallel changes in the retina. Arteriolar narrowing and enhanced arteriolar light reflex of the retina is associated with vessel abnormalities, white matter lesions and lacunes that are caused by cerebral small vessel disease8. A significant relationship was discovered between narrower retinal venules, an altered retinal microvascular network and the occurrence of Alzheimer disease. It is suggested that brains of patients have an altered cerebral microvasculature that is also observable in the retina9.
Evidence is also increasing about the correlation between retinal vascular changes and coronary heart disease10,11. The ratio between the diameter of retinal arteries and retinal veins (A/V) has been shown to be a sensitive proxy to reflect hypertension and atherosclerosis12. A narrowing of the arteries and widening of the veins, leading to a decreased A/V ratio, corroborates risk of stroke and myocardial infarction13. Hypertension can cause direct retinal ischemia and retinal infarcts that become visible as cotton wool spots and deep retinal white spots14. Serre and Sasongko recently summarized the literature and they concluded that exposure to lifestyle and environmental risk factors (e.g., diet, physical activity, smoking, and air pollution) can induce morphological changes in the retinal microvascular bed15. Importantly, such retinal changes have been associated with cardiovascular risk factors, even before clinical manifestations of diseases16.
Significant increases in the incidence of cardiovascular morbidity and mortality have been attributed to long- and short-term exposures to particulate matter air pollution17,18. Research indicates that particulate matter (PM), an important fraction of air pollution, contributes to the development of cardiovascular disease and induces cardiovascular events19,20. An impairment of the function of the microvascular bed is thought to play a role in the observed associations. In this respect, an association between exposure to air pollution and arteriolar narrowing in the retina has been reported by Adar and colleagues21. The retinal arteriolar caliber was narrower and venular caliber was wider among the 4607 participants of the Multi-Ethnic Study of Atherosclerosis (MESA) that were living in areas with increased long- and short-term exposure to PM2.5 (particulate matter &#8804; 2.5 &#956;m in diameter)21. Systemic inflammation caused by chronic air pollution exposure may result in wider venular diameters22. This corroborates&#160;the studies that report the impact of smoking on the retinal microvascular bed23. A recent publication reports on the association between short-term air pollution exposure and microvascular changes in healthy adults (22-63 years of age) measured with retinal fundus photography24. An increase in PM10 (particulate matter &#8804; 10 &#956;m in diameter) and BC (black carbon, a combustion by-product that can be used as a proxy for traffic-related diesel exhaust) was associated with a decrease in arteriolar caliber24,25.
In this scientific video protocol, the procedures are described to collect fundus pictures of the eye, to perform image analysis to obtain arteriolar and venular vessel calibers, and to calculate Central Retinal Arteriolar Equivalent (CRAE) and Central Retinal Venular Equivalent (CRVE). Retinal imaging is gaining increased attention because the retina is the only tissue that allows an unobtrusive analysis of the microvasculature and images can be collected from early age up to old age26,27. CRAE and CRVE appear to be sensitive parameters that reflect the impact of modifiable lifestyle and environmental cardiovascular disease risk factors on the microvasculature. In the manuscript, the repeatability of the vessel analysis is demonstrated. Furthermore, the applicability of retinal microvasculature analysis in epidemiological studies is shown by summarizing our findings obtained in a repeated-measures design with a focus on the impact of particulate air pollution exposure24.

<table border="0" cellpadding="0" cellspacing="0" width="970">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:321px;">Name of Material/ Equipment</td>
			<td style="width:223px;">Company</td>
			<td style="width:196px;">Catalog Number</td>
			<td style="width:231px;">Comments/Description</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Canon CR-2 nonmydriatic retinal camera&#160;</td>
			<td>Hospithera (Brussels, Belgium)</td>
			<td></td>
			<td>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&#160; be checked before starting a study.</td>
		</tr>
		<tr height="357">
			<td height="357" style="height:357px;width:321px;">IVAN: Vessel Measurement Software</td>
			<td style="width:223px;"></td>
			<td style="width:196px;"></td>
			<td style="width:231px;">This 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&#8211;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 
			&#160;</td>
		</tr>
	</tbody>
</table>

fundus photography as a convenient tool to study microvascular responses to cardiovascular disease risk factors in epidemiological studies

The microcirculation consists of blood vessels with diameters less than 150 &#181;m. 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.

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&#160;min&#160;using a retinal camera (Figures 1</str...

Watch this Scientific Journal Video about Fundus Photography as a Convenient Tool to Study Microvascular Responses to Cardiovascular Disease Risk Factors in Epidemiological Studies at JoVE.com

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

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.

The microcirculation consists of blood vessels with diameters less than 150 &#181;m. It makes up a large part of the circulatory system and plays an ...

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