Our eyes are adapted to focus in air, but not in water. To see clearly in the water, divers wear a mask to maintain a pocket of air in front of their eyes.

A suitable dive mask must include certain required functional and safety features.

Dive masks must have a nose pocket. As you'll learn later in this course, you need to be able to exhale into the mask to equalize its air pressure or clear water from the mask.

Swim goggles must never be used when diving because the air pressure inside the goggles cannot be equalized as you descend.