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V. Silvestri, J. O'Neill, G. Silvestri; Assessment of Retinal Vascular Calibre and Optic Disc Colour in Emmetropic Eyes . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2646.
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© ARVO (1962-2015); The Authors (2016-present)
To devise an easy–to–use, visually attractive and inexpensive computer–assisted method to measure retinal vessel diameter and optic disc pallor to assist in objective clinical grading of patients with Retinitis Pigmentosa.
Fundus photographs were taken through a dilated pupil from 8 healthy emmetropic volunteers, on a Topcon 50IX at the 50º angle of view. The best, normally exposed images were selected and exported to Adobe Photoshop (APS). The diameter of the optic disc (DD) was measured in millimetres in both the horizontal and vertical planes and the mean was calculated. Using this measurement and the modern assumption that 1 DD is approximately 1.8mm (1800µm), 8 measuring blocks ranging from 31 to 200µm were designed and plotted. These measuring blocks can then be superimposed on the image, zoomed to improve visualization, moved around and rotated to measure the calibre of the veins and arteries. Inferior and superior veins and arteries were measured at ½ a DD from the OD margin on the same eyes, which were used to calibrate the measuring blocks. The colour of the 4 OD quadrants was sampled on these same eyes.The colour of a normal optic disc (OD) was assessed by sampling the 4 quadrants of the ODs of 6 normal emmetropic eyes, in terms of Red, Green and Blue (RGB) using the colour sampler tool in APS. The point from which the sample was taken varied slightly to avoid vessels but was fixed for each image so sampling could be repeated.
We report the following values for the calibre of the retinal vessels and optic disc colour per quadrant in normals. It was noted that the red value was constant at 255 and only a small variation appeared in the green and blue values. Mean values were are follows:
Having devised an accurate, inexpensive and objective method for measuring the calibre of retinal vessels and for assessing optic disc colour, we propose that these measurements can be used as baseline normal values to develop an objective assessment scale for optic disc pallor and vascular attenuation in patients with RP.
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