2-37a - Vascular Features

When looking at the disc, the central retinal artery and vein should be visible. The central retinal artery is usually slightly narrower than the vein. When the central retinal artery goes though the lamina cribrosa, the artery becomes smaller because of diminution of the muscular layer and loss of the internal elastic membrane. The color of the arteries is brighter red than the veins and appears to have a lighter reflection streak as compared to the veins. The "light streak" is due to the reflection of the ophthalmoscope's light on the convex vessel wall and is a reflection off the internal limiting membrane as it covers the vessels. Branching of the arteries can occur behind the disc and lamina cribrosa, on the disc, or even off the disc. The retinal arteries emerge just nasal to the veins in the disc. The arteries and veins usually divides into superior and inferior branches and further will branch temporally and nasally--giving the superior temporal arcade, inferior temporal arcade, superior nasal arcade, inferior nasal arcade. The arteries taper as they are viewed peripherally. Pair with disc image 2-37b.