When the light is reflected, there can be so much radiation that the retina of the eye can get burns. To give the eyes a proper protection, look for sunglasses that have UV400 protection and CE marking.
UV400 stands for protection for ultra violet light up to 400 nm. The fact that the sunglasses only have dark glass does not mean that it protects well.
In fact, if the UV400 protection is not enough in a pair of dark glasses, the eye can be damaged even more when the pupil is tricked into widening to let in more light.
Grey glass generally gives the best color reproduction. Plastic glass PC (polycarbonate) provides better UV protection than mineral glass and TAC (Triacetate Lenses).