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Huiyuan Liang, Qingyuan Liang; The Angle as a Measure of the Vein Narrowing at Retinal Arteriovenous Crossings. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1555.
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© ARVO (1962-2015); The Authors (2016-present)
The narrowing of the retinal vein at an arteriovenous (AV) crossing is thought to be associated with branch retinal vein occlusion (BRVO). Monitoring the progress of vein narrowing on a patient’s fundus photos is a possible predictor of the risk of BRVO. Direct comparison of the venous caliber measured on the fundus photos may be the simplest way to do so. However, fundus photos taken at different times may have different magnifications which may result in different vein caliber readings, making comparison difficult. The degree of vein narrowing can be defined with an angle which is theoretically not affected by magnification. This study is to explore the consistency of the vein narrowing angles measured from the fundus photos of the same eyes at different magnifications.
A retrospective case-series study included 33 BRVO eyes (OD 16, OS 17) of 30 patients (male 15, female 15, age 45-88 years, mean age 67.9±11.6 years). Each eye had two fluorescein angiographic photos of post pole: one of 30° field (higher magnification), and another of 50° field (lower magnification) (Fig. 1,2). All photos were digitally enhanced by increasing sharpness to more clearly define the vasculature edges. One non-BRVO AV crossing showing visible vein narrowing was selected in each eye. The narrowing angle of the vein proximal to AV crossing was manually marked and measured three times on the digital photos using computer by two researchers separately. The mean of the three measurements was the value of vein narrowing. The differences between angles at different magnifications, and measured by the different researchers were analysed. Smaller angle discrepancy indicated better agreement.
The difference of the angle values with different magnification ranged from 0° to 10.4° (70% <5°, mean 3.6°±3.1°) with researcher 1 and (and?) 0.2° to 8.9° (64%<5°, mean 3.9°±2.6°) with researcher 2. There was no statistical significance difference between researchers.
The small mean difference of angle values at different magnifications, and good correlation between researcher angles made it possible to use angle as a measure of vein narrowing. However, accuracy and precision of the measurement requires improvement.
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