Types of diving mask:

• The old type with one big oval pane. In the oldest diving masks this window was an ellipse.
• Similar to the previous, but the window is closer to the face, and the window has a big cutout below to fit over the nose, which is kept dry by an expansion of the rubber mask edging.
• Similar to the previous, but with two windows, one window for each eye, as shown above. This type can have the windows closer to the face than the one-window type and thus contain less space for the diver to have to blow water out of if the mask floods.
• The double-dome mask. This is a new invention by HydroOptix. Double-dome masks allow a wider field of view and avoid the refraction error in perceived distance and size of objects. Underwater the curved mask windows make the diver's vision effectively more hyperopic / less myopic and the diver must wear special contact lenses to compensate (unless his eyes are myopic to the right amount to compensate exactly for the refraction at the curved mask windows); his vision will go myopic when he puts his head out of water with the contact lenses in.
• Other optional features:
  • Blowoff valve.
  • Indentations underneath for the diver to put a thumb and forefinger in to pinch the nose to aid ear clearing.
• The Data Mask, developed by Oceanic, is an eyes-and-nose diving mask with a built-in LED display which displays various dive and breathing set conditions including the function of a diving computer. It is currently very expensive.