Normally, the eye filters light by widening or closing the hole in the center of the iris, called the pupil. Emotional reactions can achieve this as well: shock might narrow the pupil, while relaxing could widen it considerably. However, in animated fare or Comic Books, this can be very hard if not impossible to show, since a typical human pupil, at its widest, is 3-4 millimeters.note This trope is a way to sidestep that difficulty. Instead of just changing the size of the pupil, you change the size of the iris (the colored ring surrounding the pupil) as well.
Your iris is no more capable of growing than your bones are of stretching like Gumby, but since they are by far the largest feature of an eye other than the whites, it's easy for artists to "expand" them to get the desired emotional reaction across.
Emotions this is meant to convey usually include love, (pleasant) surprise, desire, or awe. Animated characters experiencing the Mushroom Samba almost always get a close-up of their eyes showing this, just before reality goes sideways for them. Those effected by a Glamour, Love Potion, or Love Is in the Air effect may also get this, though those may be indicated with Mind-Control Eyes instead.
When the pupils are drawn abnormally large, the eyes generally appear pleading or wistful. That trope is Puppy-Dog Eyes.
- The animation style of Magical Girl Lyrical Nanoha usually shows an all-black pupil/iris with the anime-standard lens flare and a cresent of color near the bottom of the eye. When a character is shocked, scared, or incredibly pissed off, you can see the iris all the way around. Their eyes kind of shrink, too.
- Since just about every main character in Peacemaker Kurogane spends a lot of time indulging in Angst over past and/or current traumatic events this happens often. (The most notable characters who do this are Tetsunosuke and Suzu.)
- Done in many Reaction Shots in Serial Experiments Lain.
- Similarly used in Ghost Hound, by the same director.
- In a particularly extreme example, in Magikano, the iris opens, then the iris and pupil shrink, and the sclera fractures.
- This is used along with Hellish Pupils in Higurashi: When They Cry - probably because any character with this effect is usually in the grip of some serious paranoia.
- Train from Black Cat does this a LOT. Though, even for anime standards, his irises were already not normal, looking a lot more like a cat's. Creed also does this sometimes.
- It happens occasionally to Sousuke from Full Metal Panic!, though not too often, considering how normally unphasable he is. He's shown doing this more often during TSR, and it's noticeable in the Sigma manga as well.
- People in Mobile Suit Gundam SEED who enter SEED Mode have much larger irises, though their emotional range typically doesn't change much.
- In Naruto, this is what the 9-Tailed Fox looks like when it's being controlled by someone with the Sharingan.
- Baby Steps: This technique is used to reflect Eiichirou's shock when Kageyama suggests he knows the reason E-chan got into tennis.
Kageyama: "...you like Takasaki-san, don't you!?"Eiichirou (his irises shrinking to tiny dots): "EEEEEEEHHHHHH!?!?!"Kageyama: "What's with that reaction?"
- Chi's irises got HUGE when she saw a shopping bag filled with kitty toys. Of course, she went straight for the bag.
- Concrete can actually do this with his eyes, dilating them until there's nothing but the black of the pupils visible in order to see in the dark. According to Under the Desert Stars his eyes "dilate enormously, adding light-gathering power to their high resolution", though in a later story Maureen described his night-vision as being similar to that of a cat or dog (which doesn't explain at all why they turn black), so the original explanation of how they work may or may not have been retconned.
- Happens to Bruce in Finding Nemo as a result of him suddenly reverting back into "a mindless eating machine" after accidentally sniffing Dory's blood.
- In the Kim Possible Movie: So the Drama, Kim's iris and pupil go bigger, then smaller when she is shocked by her android boyfriend who works for Drakken and Shego.
- Santa Claus Is Comin' to Town: Kris gets these when he sees the Winter Warlock for the first time.
- Happens a lot in horror movies, when a person who's a vampire/possessed/under a spell goes from looking normal human to looking like they're a vampire/possessed/under a spell.
- Tweaked in 2004's Dawn of the Dead (2004). When the anonymous woman reanimated, we got a closeup shot of her eye turning from normal human green to that freaky occluded color.
- In the pilot of Sense8, when Riley inhales from the drug pipe, we get a close-up on her iris widening.
- The Funtastic World of Hanna-Barbera had Shaggy due this when he sees the ride vehicle very-nearly crash into the Mystery Machine.
- Dominic Deegan features irises getting huge and limpid when someone is feeling touched or romantic toward someone else.
- Truck Bearing Kibble in this strip
- Happens to Kate Beaton when she's traumatized by James Joyce's love letters.
- In Blip, Hester's irises are massive by default, larger than any other characters' (it's even lampshaded early on); a visual indication that she's the most emotional of the bunch.
- Homestuck: In the end-of-Act-5 flash, Rose comes to a sudden realization about the nature of The Tumor. Her eyes widen as the camera zooms in on them for dramatic effect, and then everything goes wrong.
- In Rusty and Co., even in minature, we can see how white Madeline's eyes get what she sees what Cube is doing.
- Bear Nuts makes heavy use of this.
- Common trope in Western Animation, especially happening to children when they are surprised by something (to the perspective of a kid) mortifying. Used at least once in nearly every Nickelodeon and Cartoon Network show.
- Avatar: The Last Airbender
- "The Desert"
Sokka: Driiiink cactus juice! It'll quench ya! Nothing's quenchier! It's the quenchiest!
- "Lake Laogai"
- "The Desert"
- In the Dexter's Laboratory short "Chicken Scratch" Dee Dee sees Dexter with chicken pox and this happens to her.
- Common trope in The Fairly OddParents.
- Futurama uses this most memorably when Lrrr ("Ruler of the planet Omnicon Persei VIII!") eats a hippie and then addresses an audience.
- In Justice League Unlimited episode "Task Force X," Plastiques iris narrows every time she has a Oh, Crap! moment.
- In Littlest Pet Shop (2012) this happens to many of the characters at times, but for the most part everyone's eyes are already so huge that this trope is almost unnecessary.
- My Little Pony: Friendship Is Magic provides the page image. The animation uses eye tropes heavily to convey emotions, and Open the Iris is used to show, just for example, epiphany, wonder, greed, insanity, terror, emphasis of a key phrase, and the sensation of burping up a scroll.
- In The Simpsons, this is one of Homer's reactions as he chows down on Krusty Burger's barbecue sandwiches, repeated along with the action itself and fat and suchlike flooding into his system (a Shout-Out to Requiem for a Dream). Also, when he licks hallucinogenic toads in another episode.
- The Spectacular Spider-Man plays with the trope. Curt Connors' iris narrows to a vertical slit, then opens back up to a normal human one. Well, sort of. None of the people in this Animated Series have pupils, just irises.
- In SpongeBob SquarePants, Gary gets this when Spongebob informs him it's time for a bath...though in his case, his pupils growing bigger means he's scared.