Ray Ban most expensive Sunglasses

The first point should be, in the grand scheme of designer eyewear,
is not that expensive. Oakley sits around the same price point as Ray Ban. They're not up there in terms of price with brands like Chanel, Tag Heuer, or Persol. However, they're more expensive than non-designer frames, typically. Oakley eyewear is (relatively) expensive for two reasons.
Oakley's technology is decent. Although they use an awful lot of their own terms for things, so it can be quite difficult to figure out what each technological improvement actually is, their lenses are of better quality than most, as well as offering improvements in other aspects of their eyewear.

Unobtainium: Special type of rubber ear sock that gets more grippy as you sweat.

HDO: "High definition optics" - Oakley's lens tech that reduces lens distortion

XYZ Optics: Oakley's lens tech that improves clarity in the peripheral vision, especially on highly curved lenses.

O Matter: Oakley's polycarbonate frame material.

Oakley C5 Alloy: Aluminium alloy material that some of Oakley's metal frames are made of.

Hydrophobic lens coating: A coating on the lens that repels water, dust and oils.

This gives a few of Oakley's technologies used in their sunglasses. All of which make them decent to look through, resistant, and lightweight. The styles are typically sports-oriented which may not make them to everyone's taste, but the frames are of good quality.

Which brings us onto branding. Oakley, or rather Luxottica who own Oakley, spend huge amounts of money on the Oakley brand. From sponsoring the world's top athletes, to funding extreme sports videos, even the design of their headquarters is all part of their extensive brand.