Encourage them to take the EnChroma Color Blind Test to determine their type of color blindness. When that is not possible, try our most popular lens for Deutans, which works for over 75% of those with red-green color blindness. Shop Outdoor Deutan or Indoor Universal for non-prescription. If you're considering ordering prescription glasses for someone, our most popular lens types are Cx3 Sun for outdoors and Cx1 Indoor for lower lighting conditions.