Complex sentence: Kay suffers from increased sensitivity to light, the latter of which being the reason he wears his trademark sunglasses to combat, as well as congenital achromatopsia, complete colorblindness, a defect of the eyes which causes legal blindness.
Split into simpler sentences: Kay suffers from increased sensitivity to light, so he wears his trademark sunglasses. He also has congenital achromatopsia, complete colorblindness, a defect of the eyes which causes legal blindness.