I've watched a fair amount of UCI world cup track racing in the past year, and I've noticed most cyclists are wearing sunglasses in indoor velodromes. Sometimes they're aerodynamic visors, but more often they are just standard sport sunglasses. Why do track cyclists wear them?
Track cyclists are travelling in excess of 30mph. At that speed you need eyewear to protect from the 'wind'.
Track cyclists reach speeds over 50 km/h. At these speeds you need to cover your eyes and sunglasses look cooler than clear glasses. Because velodromes are usually well lit, they don't affect the cyclists sight.