100 Fun Facts About Eyes

What is the term for having irises of two different colours?

Heterochromia wasn't behind David Bowie's mismatched eyes: a schoolfriend's punch in 1962 left one of his pupils permanently dilated.

Which part of the eye provides most of its focusing power?

The cornea does about two-thirds of the eye's focusing, which is why laser eye surgery can fix blurry vision by reshaping it.

Pinpoint pupils are one of the three classic warning signs of an overdose of which kind of drug?

Opioids act on the part of the brain that controls breathing, which is what makes an overdose deadly, and the medicine naloxone can prevent death if given in time.

Which Impressionist had cataract surgery in 1923?

Claude Monet put off the operation for years for fear it would worsen his sight, and paintings from his clouded years look blurrier.

Which photoreceptor cells in the retina work in dim light and see only in shades of grey?

Rods are almost absent from the centre of your gaze, which is why a faint star is easier to see when you look slightly to one side of it.

Which part of the eye, packed with cone cells, delivers the sharpest central vision?

Fovea vision is so narrow that you can't sharply read words just beyond the one you're looking at, which is why your eyes keep jumping along a line of text.

The retina is unusual among body tissues because it is technically part of what?

The central nervous system includes the retina because it grows out of the developing brain, and eye symptoms often show up before some brain diseases are diagnosed.

The natural blind spot in each eye is caused by what?

The optic nerve's exit point has no light-sensing cells, yet you don't notice the gap because your brain fills it in using the surrounding scene.

The jelly-like substance filling the back of the eyeball is called what?

Vitreous humour resists decay after death, and its potassium rises so predictably that forensic scientists use it to estimate how long someone has been dead.

Which thin membrane lines the eyelids' inside and covers the white of the eye?

Conjunctiva vessels are so fragile that a hard cough can burst one, leaving a vivid red patch that looks alarming but usually clears within two weeks.

A shortage of which vitamin is the classic cause of night blindness?

Vitamin A is plentiful in carrots, but Britain's wartime claim that carrots gave its night-fighter pilots sharper sight is said to have been cover for secret radar.

What is the age-related loss of near focusing, common after 40, called?

Presbyopia can be eased with eye drops: in 2021 US regulators approved pilocarpine drops, which shrink the pupil to sharpen near vision, much like looking through a pinhole.

What gives blue eyes their colour, since the iris holds no blue pigment?

Light scattering in the stroma turns irises with little pigment blue, and such light eyes carry a higher risk of a rare but dangerous cancer inside the eye.

The phrase 'turn a blind eye' is often linked to which naval commander?

Horatio Nelson is said to have put his telescope to his blind eye at Copenhagen in 1801 to ignore a signal to withdraw, but the phrase was in use before him.

Which dog breed is famous for often having strikingly blue eyes?

Siberian Husky blue eyes are strongly linked to a duplicated stretch of DNA, a 2018 study found after analysing thousands of pet dogs' DNA test results.

In a 1966 propaganda interview, US prisoner of war Jeremiah Denton secretly blinked which word in Morse code?

Torture was spelled out as Denton answered his captors' questions, and when the film reached US television it confirmed that American prisoners were being tortured.

Drops from which poisonous plant were reportedly once used by women to make their pupils look larger?

Belladonna gives medicine atropine, which doctors inject to speed up a dangerously slow heartbeat and to treat some pesticide poisonings.

The tears you shed while chopping onions are classed as which type?

Reflex tears flow because cutting an onion breaks open its cells, letting enzymes turn its sulphur compounds into a vapour that stings the eyes.

Which antibacterial enzyme in tears attacks the cell walls of certain bacteria?

Lysozyme was named by Alexander Fleming after he saw nasal mucus stop bacteria growing on a culture plate, years before he noticed penicillin.

Which tech company's signature blue reportedly stems from a founder who is red-green colour-blind?

Facebook founder Mark Zuckerberg is red-green colour-blind, a trait far more common in men because its genes sit on the X chromosome.

Which English chemist, colour-blind himself, lends his name to a term for the condition?

John Dalton asked for his eyes to be examined after his death, and DNA from the preserved tissue showed in 1995 that he lacked the eye's green-sensing pigment.

The dotted-circle plates used to screen for red-green colour deficiency are named after whom?

Ishihara plates include 'hidden digit' designs, meant to show a number only to people with red-green colour deficiency while staying invisible to everyone else.

In myopia, or short-sightedness, where does light from distant objects come to a focus?

In front of the retina is where a myopic eye focuses distant light, usually because the eyeball has grown slightly too long from front to back; outdoor time in childhood appears to protect against it.

A cataract is a clouding of which part of the eye?

The lens can be swapped for a plastic implant, an idea Harold Ridley developed after seeing wartime pilots' eyes tolerate plastic splinters from their shattered cockpits.

In Homer's Odyssey, which one-eyed giant does Odysseus blind to escape from his cave?

Polyphemus had been told that Odysseus's name was 'Nobody', so when the blinded giant shouted that Nobody was hurting him, his neighbours didn't come to help.

The letter chart used to test eyesight was devised in 1862 by which Dutch scientist?

Herman Snellen created the chart as a practical tool for measuring sight with the acuity formula devised by his professor, Franciscus Donders.

In '20/20 vision', what does the first 20 stand for?

Distance in feet comes first, and 20/20 isn't perfect sight: someone with 20/15 vision reads at 20 feet what an average person must be 15 feet away to read.

The first eyeglasses were made in about 1290 in which country?

Italy produced the first spectacles, but nobody knows who made them: a story crediting a Florentine named Salvino degli Armati was later exposed as a hoax.

Which American statesman is credited with inventing bifocal spectacles?

Benjamin Franklin had the lenses from his reading and distance glasses cut in half and joined into one frame, with the distance half on top.

The pupil is named after the tiny figure reflected in it, from a Latin word meaning what?

Little doll is what Latin pupilla meant, and the same family of words gave us 'pupil' for a student, first meaning an orphan in a guardian's care.

Which composer was operated on twice in 1750 by John Taylor, a travelling English eye surgeon?

Johann Sebastian Bach reportedly came out of the operations blind, and he died less than four months later, possibly weakened by complications from the surgery.

Which eye disease, often linked to raised pressure inside the eyeball, usually steals side vision first?

Glaucoma usually has no early symptoms and takes vision so gradually that about half of the people who have it don't know.

Which sea creature has eyes with 12 to 16 types of photoreceptor, against the four in human eyes?

Mantis shrimp have all those receptors, yet in tests they struggled to tell apart colours that humans distinguish easily.

Which animal has the largest eyes documented in the animal kingdom, about 27 to 30 cm across?

Colossal squid eyes may give an early warning of danger, letting the squid spot a hunting sperm whale from far away in the dark.

Owls have to swivel their heads up to 270 degrees because their eyes are what?

Fixed in tubular sockets, owl eyes stay locked in place, so the bird turns its head instead, helped by 14 neck vertebrae, twice as many as humans have.

A chameleon can watch two different objects at once because it can do what?

'Move each eye independently' is exactly what a chameleon's turret-like eyes do, scanning nearly all round; when it hunts, both eyes swing forward for stereo vision before the tongue fires.

What shape are a goat's pupils?

Horizontal slits are typical of grazing prey animals like goats, while vertical slits tend to belong to ambush predators such as domestic cats.

Each of a scallop's up to 200 tiny eyes focuses light mainly with what?

A concave mirror made of guanine crystals forms the image, and scallops are thought to use their many eyes mainly as an early warning against predators.

Which sea creature has 24 eyes, some always gazing up through the surface?

Box jellyfish of one species use those upward eyes to spot the mangrove canopy above the water and steer to the lagoon edges where they prefer to live.

The layer that makes a cat's eyes shine in headlights, which humans lack, is called what?

Tapetum lucidum in reindeer turns from gold in summer to deep blue in winter, making their eyes more sensitive in the Arctic dark at the cost of sharpness.

The red-eye effect in flash photographs is mainly caused by light bouncing off which layer of the eye?

The choroid gives the usual red glow, so a pupil that looks white instead of red in a child's flash photo can be a sign of the eye cancer retinoblastoma.

Which bird can see all around while probing the soil with its long bill?

Woodcock eyes sit so far back that the bird can keep watch for danger even while its long bill is buried in the soil hunting earthworms.

Which retinal cells, identified in 2002, sense light directly and help set the body clock?

Photosensitive ganglion cells keep working without the eye's usual light receptors: in a profoundly blind man, blue light still reset his body clock and boosted his alertness.

What does the seventh extraocular muscle in each orbit do?

Lifting the upper eyelid is the job of the levator palpebrae superioris, and when this muscle is weakened or damaged, the eyelid droops, a condition called ptosis.

In which direction does a single human eye see furthest while looking straight ahead?

Outward, toward the temple, each eye's field reaches past 90 degrees from where it's looking, so you can spot something moving beside you without turning your eyes.

Which lobe of the brain initiates voluntary saccades, the rapid jumps both eyes make together?

The frontal lobe's eye fields launch each voluntary jump, and the brain suppresses the motion signals each jump creates, so the world doesn't seem to smear as your eyes dart.

When your eye focuses on something close, the flexible structure just behind the iris changes into what shape?

More convex shape follows when a ring of muscle tightens: in Hermann von Helmholtz's classic 19th-century model, that slackens the fibres that otherwise pull the structure flat.

What is the greyish-white ring of fatty deposits that can appear around the iris called?

Arcus senilis is usually harmless in older people, but when it shows up in someone under 50, doctors may check their cholesterol for an underlying lipid disorder.

Which two pigments give the macula its yellow colour and feature in supplements for macular degeneration?

Lutein and zeaxanthin took the place of beta-carotene in the updated eye-supplement formula, which suits smokers better, since beta-carotene raises their lung cancer risk.

Which pigment in the retina's dim-light cells, bleached by bright light, must rebuild before your eyes adjust to the dark?

Rhodopsin faults caused by some gene variants make the pigment switch on even in darkness, scrambling the eye's signals and causing night blindness that doesn't worsen over time.

Second World War propaganda claimed which vegetable let RAF pilots see in the dark, to hide radar?

Carrots took the credit for British night-fighter successes that were really down to newly adopted radar. Eating them only sharpens sight in the dark for people whose diet is deficient.

Which rock star's pupil stayed permanently dilated after school friend George Underwood punched him?

David Bowie's mismatched-looking eyes were the lasting result, and they became one of his most recognisable features. He stayed on good terms with Underwood, who later created artwork for his early albums.

Which lizards, most of which cannot blink, use their tongues to wipe their own eyes clean?

Geckos have a clear protective scale over each eye, so a quick lick is how they wipe away dust and dirt. The habit also keeps the surface of the eye moist.

Which English scientist slid a needle-like bodkin behind his own eyeball to study how we see colour?

Isaac Newton wrote in his notebook that white, dark and coloured circles appeared as he pressed. They looked plainest while he kept the tip of the bodkin rubbing against his eye.

Which English king is traditionally said to have died from an arrow in the eye at Hastings?

Harold Godwinson fell in 1066 as the last crowned Anglo-Saxon king of England. The Bayeux Tapestry shows a figure gripping an arrow at his eye, though historians debate how the king really died.

Which wildflower, whose head closes at night, is named from the Old English for 'day's eye'?

Daisy began as the Old English dæges eage and had worn down to daiseie by about 1300. The whole flower head shuts at dusk and reopens in the morning light.

Which flightless bird has the largest eyes of any land vertebrate, each about 5 cm across?

Ostrich eyes help the bird see predators such as lions from far away. They also sit high, since the long neck and legs can lift its head up to 2.8 metres above the ground.

Which Norse god gave up one of his eyes in exchange for a drink from Mímir's well of wisdom?

Odin left his eye in the well as a pledge, the Prose Edda relates, and only then was he allowed a single drink. Mímir himself is said to drink from the same spring every morning.

Which sea creature rests only half its brain at a time, keeping one eye open as it sleeps?

Dolphin sleep shuts down one half of the brain along with the opposite eye, while the other half stays alert. The waking half also signals when to rise to the surface for a fresh breath of air.

Which Frenchman, blinded as a boy by an awl in his father's workshop, devised a raised-dot alphabet?

Louis Braille was three when the awl slipped, and infection then spread to both eyes. He had worked out his raised-dot code by the time he was fifteen.

In Greek myth, Hera set the hundred eyes of her slain watchman Argus into the tail of which bird?

Peacock feathers kept the eyes forever, Hera's tribute to the giant who had guarded the heifer Io until Hermes killed him on Zeus's orders. In another telling, she turned Argus himself into the bird.

Elizabeth Taylor's eyes, rimmed by double lashes from a genetic mutation, were blue but looked which colour?

Violet was only the appearance, but her eyes drew particular attention all the same. She went on to play the Egyptian queen in the 1963 epic Cleopatra.

Which band recorded 'Eye of the Tiger' after Sylvester Stallone asked them for a Rocky III theme song?

Survivor got the call only after Queen refused Stallone permission to use 'Another One Bites the Dust'. The replacement spent six weeks at number one on the Billboard Hot 100.

The Eye of Providence, floating above an unfinished pyramid, appears on the back of which US banknote?

One-dollar bill designs have carried the eye since 1935, when the reverse of the Great Seal was added to the note. The seal itself had adopted the symbol back in 1782.

The wedjat, an Egyptian eye amulet of healing and protection, shows the eye of which falcon god?

Horus lost the eye in a conflict with his rival Set, who tore it out or destroyed it. Another deity then restored it, which is why the name wedjat means the whole or uninjured eye.

Which American television network has used a stylised eye as its trademark logo since October 1951?

CBS is sometimes called the Eye Network as a result. Designer William Golden based the mark on a Pennsylvania Dutch hex sign and a Shaker drawing.

Which animals pull their eyeballs down through holes in the skull to help push food down the throat?

Frogs seize prey with a sticky tongue and swallow it whole. Sinking the eyes into the head then helps to force the meal toward the stomach.

Which crooner ended a short retirement in 1973 with the album and TV special 'Ol' Blue Eyes Is Back'?

Frank Sinatra owed the nickname to his deep blue eyes. He had retired in 1971, but was back within two years with the album and a television special of the same name.

Insincere displays of grief are named after which reptile, long said to weep over the victims it eats?

Crocodile tears are real, but they only lubricate the eyes, mostly after the animal has been out of water for a long time. A rare condition that makes people cry while eating borrows the name.

Steve McCurry's portrait of a green-eyed Afghan refugee girl made the June 1985 cover of which magazine?

National Geographic has called it the most recognised photograph in its history. The girl stayed anonymous until 2002, when a team from the magazine found Sharbat Gula and confirmed her identity by iris recognition.

Which one-eyed green monster, voiced by Billy Crystal, is Sulley's best friend in Monsters, Inc.?

Mike Wazowski nearly never existed, since early versions of the story gave Sulley no sidekick at all. Billy Crystal took the part after regretting that he had turned down Buzz Lightyear.

Which singer spent nine weeks at number one in the US in 1981 with 'Bette Davis Eyes'?

Kim Carnes was covering a song that Jackie DeShannon co-wrote and first recorded in 1974. After it won two Grammys, Bette Davis hung gold and platinum records from Carnes on her wall.

The giant billboard eyes of Doctor Eckleburg stare out over a valley of ashes in which American novel?

The Great Gatsby places the faded advertisement near George Wilson's garage. Ernest Hemingway claimed F. Scott Fitzgerald told him that the book's celebrated cover art referred to that billboard.

Which TV detective star's trademark squint came from an artificial eye worn since the age of three?

Peter Falk lost his right eye to a tumour as a small child. An agent warned that the replacement would cost him film work, yet he went on to win four Emmys as the rumpled Lieutenant Columbo.

In which Shakespeare tragedy does Iago warn that jealousy is 'the green-eyed monster'?

Othello hears the warning from the very man who is stoking his suspicions, in a line that says the monster 'doth mock the meat it feeds on'. The phrase helped tie the colour green to envy.

The 'eye for an eye' principle underlies a law code carved in stone for which king of Babylon?

Hammurabi had laws 196 and 200 prescribe an eye for an eye and a tooth for a tooth. The tall basalt slab that carries them was rediscovered in 1901 and now stands in the Louvre.

Which blue glass eye bead, an amulet known in Turkey and Greece, is meant to ward off the evil eye?

Nazar beads answer a curse that believers think can be cast with just one look. Each stares back with an eye of its own, built from circles of dark blue, white, light blue and black.

Which early Christian martyr, patroness of the blind, is often painted holding her own eyes on a plate?

Saint Lucy lost her eyes in medieval accounts of her martyrdom, and they were found miraculously restored at her burial. Her name echoes lux, the Latin word for light.

In Greek myth, which hero stole the single eye that the three Graeae sisters passed between them?

Perseus snatched the eye in mid-pass and held it to ransom until the sisters told him what he needed to know to kill Medusa. The grey-haired trio also had just one tooth to share.

Which American painter of big-eyed figures saw husband Walter claim her work until a courtroom 'paint-off'?

Margaret Keane won the credit for her own pictures after Walter refused to pick up a brush in a Hawaii court. Tim Burton, who collected her art, told the story in his 2014 film Big Eyes.

Vivid dreaming is linked to which phase of sleep, named for the way the sleeper's eyes dart about?

REM stands for rapid eye movement, which researchers defined and tied to dreams in 1953. While the eyes flick about, the rest of the body loses muscle tone and lies almost completely paralysed.

Which English poet, totally blind by 1652, dictated his greatest epic to a series of helpers?

John Milton composed Paradise Lost between 1658 and 1664 without being able to see a line of it. One of his best-known sonnets, on losing his sight, begins 'When I consider how my light is spent'.

What name is given to the round opening in the dome of Rome's Pantheon?

Oculus is the Latin word for 'eye', and the Pantheon's is open to the sky. It also lightens the concrete dome at the very top, where it would be weakest.

In Sophocles' tragedy, which king of Thebes blinds himself with brooch pins on learning he married his mother?

Oedipus takes the pins from the dress of Jocasta, his wife and mother, after she has hanged herself. He had won her hand and the throne by answering the riddle of the Sphinx.

Which cosmetics brand began when Thomas Lyle Williams saw his sister darken her lashes with Vaseline and coal dust?

Maybelline joins the sister's name, Mabel, to Vaseline. Williams founded the firm in Chicago in 1915 and brought out a cake mascara two years later.

The iris of the eye shares its name with Iris, the Greek goddess who personified what?

The rainbow lent its Greek name to a part of the eye that comes in many colours. Iris herself served the Olympian gods as a winged messenger, especially Hera.

Red-green colour blindness is far more common in men because the opsin genes involved are carried on what?

The X chromosome comes singly in men, so one affected copy of a gene is enough. Women have a second X whose normal copy can override it, which is why about 1 in 12 males but only 1 in 200 females are affected.

What are the swirls and flashes of light seen when you rub your closed eyes called?

Phosphenes appear because pressure sets off the eye's light detectors mechanically, with no light involved. The word was coined by Henri Savigny, ship's surgeon on the wrecked French frigate Méduse.

Which spectacles, at peak popularity around 1880 to 1900, have no earpieces and grip the bridge of the nose?

Pince-nez wearers often tethered them to their clothing with a chain, cord or ribbon, because the frames did not always stay put. A golden pair is the key clue in a Sherlock Holmes mystery.

The Richat Structure, a 40 km bullseye of rock rings nicknamed the Eye of Africa, lies in which country?

Mauritania owes the rings to an eroded dome, pushed up by molten rock from below, with the oldest layers exposed at the centre. The formation lies near the desert town of Ouadane.

Which sunglasses brand did Bausch & Lomb create in 1936 to cut the glare of the sky for pilots?

Ray-Ban began with a prototype called Anti-Glare, which paired plastic frames with green tints. A metal-framed redesign the following year was patented as the Aviator.

In which fish does one eye migrate to the other side of the head as the young fish grows?

Flounder larvae hatch with one eye on each side, like any other fish. After the change, both eyes sit on the side that faces up, and which side that is depends on the species.

Which Arctic animal's eyes change from gold in summer to blue in winter to cope with months of darkness?

Reindeer make the switch in a reflective layer at the back of the eye, which improves their vision in continuous darkness. They can also see ultraviolet light, well below the human threshold.

Which sea creature has a simple eyespot at the tip of each of its arms?

Starfish eyespots are each made of 80 to 200 simple light-sensing units. Some species turn up the tips of their arms as they crawl, exposing the spots to their surroundings.

Which small nocturnal primate has eyeballs that are each as large as its entire brain?

Tarsier eyeballs measure about 16 millimetres across. The animal can also turn its head 180 degrees in either direction, which lets it see all the way around.

Which reptile, the only living member of a dinosaur-age order, has a third eye on top of its head?

Tuatara have the most pronounced third eye of any living four-limbed animal, though it shows only in hatchlings, as a translucent patch on the skull. The species lives wild only in New Zealand.

Which extinct sea creatures, common as fossils, saw the world through eyes made of the mineral calcite?

Trilobites built their eyes from the same mineral that hardened their outer shells. Even the earliest known ones, from about 521 million years ago, already had complex compound eyes.

Which deep-sea fish looks up at its prey through the transparent dome of its own head?

Barreleye fish keep their eyes enclosed in a see-through dome of soft tissue. The eyes usually gaze upward to catch the silhouettes of prey, but they can also be directed forwards.

What name is given to the many individual units that make up an insect's compound eye?

Ommatidia are typically hexagonal in cross-section and about ten times longer than they are wide. Large dragonflies have around 30,000 of them.

The Seeing Eye, founded in 1929, is the oldest school in the United States for training which animals?

Guide dogs caught the attention of the school's co-founder, a blind 19-year-old from Nashville, when a magazine article about them was read to him. He named his first dog Buddy, and every one after her.