Eyes
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This eye trivia quiz has 100 free questions with answers and covers the human eye and vision from the cornea to the visual cortex: how big an eyeball is, what the iris and lens do, rods and cones, the blind spot, why blue eyes have no blue pigment, how rare green eyes are, why babies blink so little, the three kinds of tears, colour blindness and who first described it, myopia's rise in East Asia, cataracts and the first artificial lens. Then it goes wider: the mantis shrimp's 12 to 16 photoreceptor types, the colossal squid's dinner-plate eyes, owls that cannot move their eyes, goats' horizontal pupils, scallops with 200 mirror eyes and jellyfish with 24 eyes and no brain. History rounds it out with Ibn al-Haytham, the first spectacles in Italy, Snellen's chart, the first corneal transplant, contact lenses and LASIK. It is written for science classes, optometry students, pub quiz rounds and the curious. Easy questions cover the parts of the eye everyone learns at school; hard ones ask about photoreceptor counts and who patented laser eye surgery. Every answer has been checked against a reliable source and each question shows its citation once you have answered.
30 of 100 questions with answers and explanations. Play the quiz
Q 01What is the term for having irises of two different colours?
Heterochromia
Heterochromia wasn't behind David Bowie's mismatched eyes: a schoolfriend's punch in 1962 left one of his pupils permanently dilated.
Q 02Which part of the eye provides most of its focusing power?
The cornea
The cornea does about two-thirds of the eye's focusing, which is why laser eye surgery can fix blurry vision by reshaping it.
Q 03Pinpoint pupils are one of the three classic warning signs of an overdose of which kind of drug?
Opioids
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.
Q 04Which Impressionist had cataract surgery in 1923?
Claude Monet
Claude Monet put off the operation for years for fear it would worsen his sight, and paintings from his clouded years look blurrier.
Q 05Which photoreceptor cells in the retina work in dim light and see only in shades of grey?
Rods
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.
Q 06Which part of the eye, packed with cone cells, delivers the sharpest central vision?
Fovea
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.
Q 07The retina is unusual among body tissues because it is technically part of what?
The central nervous system
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.
Q 08The natural blind spot in each eye is caused by what?
The optic nerve's exit point
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.
Q 09The jelly-like substance filling the back of the eyeball is called what?
Vitreous humour
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.
Q 10Which thin membrane lines the eyelids' inside and covers the white of the eye?
Conjunctiva
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.
Q 11A shortage of which vitamin is the classic cause of night blindness?
Vitamin A
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.
Q 12What is the age-related loss of near focusing, common after 40, called?
Presbyopia
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.
Q 13What gives blue eyes their colour, since the iris holds no blue pigment?
Light scattering in the stroma
Q 21Which English chemist, colour-blind himself, lends his name to a term for the condition?
John Dalton
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.
Q 22The dotted-circle plates used to screen for red-green colour deficiency are named after whom?
Ishihara
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.
Q 23In myopia, or short-sightedness, where does light from distant objects come to a focus?
In front of the retina
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.
Q 14The phrase 'turn a blind eye' is often linked to which naval commander?
Horatio Nelson
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.
Q 15Which dog breed is famous for often having strikingly blue eyes?
Siberian Husky
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.
Q 16In a 1966 propaganda interview, US prisoner of war Jeremiah Denton secretly blinked which word in Morse code?
Torture
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.
Q 17Drops from which poisonous plant were reportedly once used by women to make their pupils look larger?
Belladonna
Belladonna gives medicine atropine, which doctors inject to speed up a dangerously slow heartbeat and to treat some pesticide poisonings.
Q 18The tears you shed while chopping onions are classed as which type?
Reflex
Reflex tears flow because cutting an onion breaks open its cells, letting enzymes turn its sulphur compounds into a vapour that stings the eyes.
Q 19Which antibacterial enzyme in tears attacks the cell walls of certain bacteria?
Lysozyme
Lysozyme was named by Alexander Fleming after he saw nasal mucus stop bacteria growing on a culture plate, years before he noticed penicillin.
Q 20Which 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.
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.
Q 24A cataract is a clouding of which part of the eye?
The lens
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.
Q 25In Homer's Odyssey, which one-eyed giant does Odysseus blind to escape from his cave?
Polyphemus
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.
Q 26The letter chart used to test eyesight was devised in 1862 by which Dutch scientist?
Herman Snellen
Herman Snellen created the chart as a practical tool for measuring sight with the acuity formula devised by his professor, Franciscus Donders.
Q 27In '20/20 vision', what does the first 20 stand for?
Distance in feet
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.
Q 28The first eyeglasses were made in about 1290 in which country?
Italy
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.
Q 29Which American statesman is credited with inventing bifocal spectacles?
Benjamin Franklin
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.
Q 30The pupil is named after the tiny figure reflected in it, from a Latin word meaning what?
Little doll
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.