The amount of sun exposure that your eyes get is important. That is exposure without sun glasses. It may be that UVB light, which cannot penetrated sun glasses, works to maintain eye health. One of the problems with airplane pilots is that years of exposure at high altitude of UVA without the UVB component that is blocked out by the windows and sun glasses is damage to the eyes. A study in Iceland found that pilots were three times more likely to develop age related eye disease that non-pilots.
It is always a good idea to let your eyes be exposed to natural sunlight for ten to fifteen minutes per day. Do this and then put on the sun glasses.