Frames of Reference

While glasses are universally seen as a sign of intelligence, in anime it's the shape of the frames that's telling of the personality. Generally speaking, characters with rectangular or square frames tend to have "harsher" personalities that range from emotionally distant to downright evil. Characters with the circular frames (they can be ovals or perfect circles, depending on how serious the work is) have more "soft" personalities that range from comically nerdy to shy and sweet.

Also, while someone with square frames will be more prone to Scary Shiny Glasses, people with round glasses will have their moments too; if anything, it's scarier seeing the sweet-tempered meganekko suddenly have opaque lenses then the square-framed Mad Scientist.

This trope could possibly be an extension of Tsurime Eyes and Tareme Eyes, as characters with Tsurime Eyes eyes will generally wear square frames while someone with Tareme Eyes will usually opt for round frames.

Tropes involving rectangular frames:


 * Bespectacled Bastard Boyfriend
 * Stoic Spectacles
 * Four Eyes, Zero Soul
 * A Tsundere character will have these if he or she wears glasses. Especially if she's a pushy Class Representative or Student Council President.

Tropes involving round frames:


 * Meganekko
 * Nerd Glasses
 * The Short Guy with Glasses

Tropes for either:


 * Eye Glasses
 * Hot Librarian
 * Mad Scientist: Depending on whether he's a lovable Cloudcuckoolander or a Complete Monster.
 * Opaque Lenses
 * Purely Aesthetic Glasses
 * Scary Shiny Glasses

Unrelated tropes:


 * Sinister Shades and Cool Shades: Sunglasses don't count, as they're not seen as a sign of intelligence. Simply wearing a pair, regardless of shape, makes you either sinister or cool (or both).

Anime & Manga

 * Gendo Ikari from Neon Genesis Evangelion has somewhat rectangular frames but they are rounded at the ends. Sometimes, the light reflects off them enough to hide his eyes, cluing the audience in to his inhumane nature.
 * Bleach seems to love this trope. You can pretty much tell a character's alliance or personality based on the shape of their glasses:
 * Uryuu Ishida, while not a villain, is the hero's former rival and antagonist. Is very reserved, and depending on the person, rather cold.
 * Ishida's father wears almost rectangular glasses, but is even more emotionally distant than his son.
 * Tessai Tsukabishi is rather stoic and intimidating, so his rectangular glasses suit him perfectly.
 * Ironically, in Aizen's case, the rectangular glasses were part of his "nice guy" facade and he ditches them once he outs himself as the story's Big Bad. Perhaps he couldn't quite hide his evilness as well as he thought...
 * Szayel Aporro Granz is a sadistic Mad Scientist who wears hipster glasses.
 * For round glasses we have Nanaos Ise, a comically uptight Sugar and Ice Personality who is staunchly good.
 * Nanao's predecessor Risa Yadomaru also sports round glasses, perhaps to purposely invoke the meganekko look since she also wears a school uniform.
 * Then we have Chizuru, who has triangle shaped glasses, probably to reflect her rather...eccentric personality.
 * Shirai-sensei from Kodomo no Jikan is quite the Stern Teacher, but her actual personality isn't anywhere near as harsh as it first appears and she wears the oval type glasses. Mimi is shy and naturally her glasses are the circular type.
 * Hetalia:
 * The countries, America and Canada, have this as one of their differentiating features (not that anyone notices). Canada is shy and nice so he wears circular frames while America is abrasive and somewhat arrogant so he wears square frames.
 * Austria's frames are square with rounded edges since he's a Sugar and Ice Personality.
 * Estonia's are square with rounded edges since he's generally a Nice Guy/Only Sane Man.
 * Cameroon and Sweden's glasses are square framed since they're both Stoic Spectacles.
 * Thailand has circular frames since he's cheerful and fun loving.
 * Saiyuki has an interesting example, in that Cho Gonou is shown with square glasses, while Cho Hakkai has a single round monocle instead.
 * Lampshaded in Slam Dunk, Kogure wears circular glasses while Hanagata wears square ones.
 * Barnaby from Tiger and Bunny wears hexagonal glasses (which can be seen as something of a cross between rectangular and circular lenses) and starts the series as both a Stoic Spectacles with Tsurime and a Kuudere who sometimes treads into Tsundere territory. He does, however, change quite a bit as the series progresses.
 * Father Alexander Anderson from Hellsing wears perfectly round glasses and is shown to be a gentle and rather amiable man. But in battle, his glasses immediately turn an opaque blue and he sports a seemingly constant Slasher Smile. Alucard himself sports a Slasher Smile and round glasses, but is an amoral vampire willing to take out an army of Mooks without hesitation.

Comic Books

 * Clark Kent's Nerd Glasses are horn rimmed and not quite rectangular, the closest you can get to the "round=nerdy" part of this trope realistically.
 * In Kingdom Come, Edward Nigma (aka the Riddler) wears round bifocals that scarecly resemble question marks which fit his nerdy personality and alludes to his former life of crime.

Film (Live Action)

 * The Matrix. Inside the simulation, the humans wear oval shades, while the Agents wear rectangular ones. In the sequels, as Neo and Smith become Not So Different, Neo's shades become more angular and Smith's become more rounded.

Video Games

 * In the visual novel Katawa Shoujo, the intelligent, aggressive Student Council President wears rectangle frames. In contrast, the shy librarian Yuuko had oval shaped lenses (until her recent, more realistic re-design).