Conjoined Eyes

Has anyone ever noticed that Sonic doesn't have two eyes, but one hideously malshapen eye with two pupils? Seriously, look at it! There's nothing dividing his eyes, it's like two egg whites that have fused together.

—Linkara

Eyes say a lot about a character. Color, size, and even placement can tell you if the character's built for a certain genre. For example, eyes set very close together tend to belong to characters destined for cartoon fantasy.

Sometimes artists go overboard and draw eyes where the sclerae meet in the middle, with the two pupils still occupying their own sides, never crossing into the other. With this particular physiology, the character actually possesses one gigantic eyeball in their head with two pupils on it.

Funnily enough, this passes as an Acceptable Break From Reality as the eyes, strangely constructed as they are, still do the job of conveying emotion just as well as separate eyes do. Although nobody in-universe ever seems to point out how strange it is.

Compare Sphere Eyes, which uses two giant eyeballs that have either tiny little dots for pupils or just normal pupils.

Examples of Conjoined Eyes include:

Film

Every character in the Disney/Pixar Cars franchise. Justified, as it's basically their windshields.
- Almost every character, as of the sequel. Remember that scene where Mater freaks out because of that one car in Paris?
- And of course buses and trucks have their eyes separate too.
- As with some cars, such as Sheriff, Fillmore, and Sarge, who all have vertical lines down the middle of their windshields that separate their eyes.
- This was even applied to characters whose bases in real life do not have windshields, such as Francesco Bernoulli, and characters whose bases otherwise have asymmetrical cockpits (such as the dump truck Mater knocked over in the prologue, whose cockpit is actually moved to the center of his body, and the double-decker buses in London, whose cockpits are changed into monocles). Also, for some reason there are no convertibles (they all have their roofs down) in this universe, with their windows being completey opaque, implying that they all may not be hollow.
The Voyages Of Young Doctor Dolittle has the two-pupil eyeball variant on a lot of animal characters.

Live Action Television

Just about every character in BJ and the Dirty Dragon Show/Gigglesnort Hotel.

Comic Books

Cerebus the Aardvark has no division between his eyes, this is even drawn attention to when he has to have one eye bandaged for a while.
The Smurfs, especially in the animated series. Although this probably isn't intentional, as a division between their eyes is implied.
Dennis the Menace UK, Depending on the Artist.

Newspaper Comics

Several characters in Bloom County and its follow-ups, particularly Opus.
The default style for Tumbleweeds.

Video Games

The hedgehogs (Amy, Shadow, Silver) in Sonic the Hedgehog, but none of the other characters.
- As pointed out here and here. Warning: Potential Nightmare Fuel.
Ty the Tasmanian Tiger
In the Donkey Kong series, you have Diddy and Dixie. It's also rather hard to tell behind his specs, but Cranky also has this going on. More obscure examples include Donkey Kong Jr., Kiddy Kong, and (oddly) Swanky Kong.
In Toki Tori, the titular egg-shaped chick has large eyes connected so close together that they seem to be one big eye with two pupils.
In Eversion, the cute monsters' eyes gradually become like this as you evert from World X-1 to X-3. Evert to X-4 and beyond, and their eyes fuse into one eye.
Inverted with Duskull from Pokémon: It has two eyes sharing a pupil!

Web Comics

Exterminatus Now, since it's based on the Sonic look. Example (last panel)
Captain Tagon from Schlock Mercenary.
- And his father, Kaff Tagon
Dummy Duck all three main characters' eyes when fully opened.

Web Original

Unskippable remarked on this trope during one of the episode on a Sonic Game. They also noted that, with more modern graphics and pre-rendered cinematics, it makes Sonic's eyes (eye?) look particularly creepy, as the more "realistic" detailing from the CGI clashes with this otherwise cartoonish design.

Western Animation

Goofy, Pluto the Pup, Clarabelle Cow, Horace Horsecollar, and Pete from the Classic Disney Shorts.
- Mickey Mouse is an interesting example. In his first two cartoons he has large googley eyes with a clear separation, but by "Steamboat Willie" the outlines disappear and the pupils become the eyes, while the rims become eyebrows. Occasionally, however, the "eyes" would move around the face, and if it's dark the whole eye-brow area lights up. As animation became more realistic, Mickey's design began to seem weird and unnatural, so he was redesigned with eyes that have pupils.
Many Looney Tunes characters have these during wild takes, even characters like Bugs Bunny, whose eyes are usually not that close together.
Dr. Robotnik from The Adventures of Sonic the Hedgehog.
- Actually his eyes are the red dots, the whole black area is some sorta mask based on the American Kirby Is Hardcore version of his game design.
The Snorks
The Disney animated short Suzie the Little Blue Coupe, which apparantly inspired the character designs for Cars.