Most varieties of glass and plastic block a considerable amount of UV unless they are specifically designed to be transparent to those wavelengths (e.g., pure silica glass). A moderate amount of UVA gets through, and shorter frequencies are largely blocked. I don't know exactly what formulation is used in Cessnas, but it seems unlikely that it would be an exception to this rule.
Nevertheless, given the intensity of sunlight and UV at high altitudes, it can't hurt to wear a good pair of sunglasses, not only to help preserve night vision but to help filter out any residual UV light. Prolonged exposure to UV is correlated with some degenerative changes in the eye, such as macular degeneration, especially in smokers. It's easy to find good sunglasses that block all UV entirely.