From the Metal Gear Wiki

"Those are high-performance binoculars made especially for the military."

— Sigint

The binoculars are used by Naked Snake during the Virtuous Mission and Operation Snake Eater. They are strong binoculars made especially for the U.S. military. They are waterproof and are filled with nitrogen gas to prevent lens fog. The eyepiece, objective lenses, and prism have been coated to reduce glare and can work fairly well in dark places.