In a few The Avengers episodes Steed wears glasses, such as in The Yellow Needle, The Grandeur That Was Rome, The Mauritius Penny and Intercrime.
That's the "Hipster Steed" look.

Funky Steed can be seen in TNA Trap, Steed in John Lennon style in TNA Faces.

Steed preserves glasses in his desk drawers in Return of the Cybernauts, he's looking through glasses in From Venus With Love.
The Grandeur that was Rome The Grandeur that was Rome The Grandeur that was Rome The Mauritius Penny
Intercrime Intercrime TNA Faces TNA Trap From Venus with Love
The Man with two shadows A chorus of frogs The House that Jack bulit

Patrick Macnee is wearing glasses on many on set photos, especially from series 6.
NightwearHomeCarnation and other Flowers
Steed is wearing welding goggles in Thingumajig.
Steed with a gas mask in You'll Catch Your Death
He's wearing stylish cat-eyes sun glasses in Man with Two Shadows and A Chorus of Frogs, he also wears them on photos from his holidays in The House That Jack Built.

The sun glasses seem to be Patrick Macnee's as he used them on set of The Undertakers.
on set of
The Undertakers