P3 Sunglasses
Photo/Jeff Harris

The perfect pair of sunglasses can pull your entire getup together, and this season the style to wear is a classic design called the P3. Although the name sounds state-of-the-art, the shades are nearly as retro as they come—based on military-issue eyeglasses from the 1930s, but modernized with a few interesting twists.

"The hottest look is what's called a P3 shape, sort of a drooping circle that many consider the most classic frame style in eyewear. It has also been called the Preppy in the past," says James Spina, editor in chief of 20/20, a trade magazine for the optical industry.

Originally manufactured in wire frame, the military specs were designed to fit comfortably under gas masks. But much as with combat boots, peacoats and leather bomber jackets, the public caught on to the style and wore them even when out of uniform. When the eyeglasses were later crafted with thicker frames, the P3 took on a scholarly, owlish look (Reference Gregory Peck as Atticus Finch in To Kill a Mockingbird).

The P3 derives its name from the optician's term, pantoscopic, which refers to the tilt of the lens, with the numeral three referencing the difference in millimeters between the horizontal and vertical lens measurements. The measurements are what give the P3 lenses their unique, round shape. Most P3s feature a keyhole-style nose bridge and the frames are typically made from zyl acetate or metal. A popular trend among P3 sunglasses these days is to include a secondary bridge over the two lenses, reminiscent of another type of eyewear with a military origin—aviator sunglasses.

"The new sun[glass] versions are mainly plastic (we call it zyl) but there are metal versions as well and nearly all of them play with a sort of double-bridge design element borrowed from the aviator," Spina says.

This summer, check out Ermenegildo Zegna for a classic P3 with its Champagne Chevron Sunglasses (second from top, $350). John Varvatos delivers an interesting take on the P3 called Sullivan (bottom, $318) that eschews the traditional nose bridge for an aviator-inspired secondary bridge. Ray Ban showcases two varieties of P3 sunglasses: RB 4266 (top, $215), with brown gradient lenses; and RB 4256 Gatsby I (second from bottom, $175), in tortoise shell with green mirrored lenses. Both pairs feature metal double-bridges. Lastly, Tom Ford offers a powerful-looking P3 called Clint (third from top, $395), in black acetate with green lenses.

Visit johnvarvatos.com, ray-ban.com, tomford.com and zegna.us