Abstract
BackgroundSummarised retinal vessel diameters are linked to systemic vascular pathology. Monochromatic images provide best contrast to measure vessel calibres. However, when obtaining images with a dual wavelength oximeter the red-free image can be extracted as the green channel information only which in turn will reduce the number of photographs taken at a given time. This will reduce patient exposure to the camera flash and could provide sufficient quality images to reliably measure vessel calibres.MethodsWe obtained retinal images of one eye of 45 healthy participants. Central retinal arteriolar and central retinal venular equivalents (CRAE and CRVE, respectively) were measured using semi-automated software from two monochromatic images: one taken with a red-free filter and one extracted from the green channel of a dual wavelength oximetry image.ResultsParticipants were aged between 21 and 62 years, all were normotensive (SBP: 115 (12) mmHg; DBP: 72 (10) mmHg) and had normal intra-ocular pressures (12 (3) mmHg). Bland-Altman analysis revealed good agreement of CRAE and CRVE as obtained from both images (mean bias CRAE = 0.88; CRVE = 2.82).ConclusionsSummarised retinal vessel calibre measurements obtained from oximetry images are in good agreement to those obtained using red-free photographs.
Highlights
Summarised retinal vessel diameters are linked to systemic vascular pathology
While the arterio-venous ratio (AVR) is a poor marker of vascular changes at the retinal level [3, 4], central retinal arteriolar equivalent (CRAE) and central retinal venular equivalent (CRVE) have been shown more clinically useful
In hypertensive patients for example, a decreasing CRAE over time is associated with increased arterial stiffness and has shown potential to be predictive in regards to cardiovascular mortality and morbidity
Summary
Summarised retinal vessel diameters are linked to systemic vascular pathology. Monochromatic images provide best contrast to measure vessel calibres. When obtaining images with a dual wavelength oximeter the red-free image can be extracted as the green channel information only which in turn will reduce the number of photographs taken at a given time This will reduce patient exposure to the camera flash and could provide sufficient quality images to reliably measure vessel calibres. In hypertensive patients for example, a decreasing CRAE over time is associated with increased arterial stiffness (in early-stage hypertension) and has shown potential to be predictive in regards to cardiovascular mortality and morbidity. This provides data on the potential of CRAE to become a useful marker for risk stratification in hypertensive (HT) patients [5]. A decrease in CRAE and an increase in CRVE over time are predictive of microvascular outcome in type 1 Diabetes Mellitus (DM) [8]
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