ciliary muscleThe muscle that tunes the eye for near and far. It is a ring of smooth muscle, so it works without being told. It changes the shape of the lens.
conesThe color detectors packed at the retina's center. They work in daylight, and each kind responds best to its own part of the spectrum. A human eye has about six million cones.
corneaThe front layer that supplies most focusing power. It is the clear dome at the very front of the eye. It supplies about two thirds of the focusing power, and the lens most of the rest.
eyelidThe movable cover that wipes the eye with each blink. Lashes grow along its edge and help to keep dust out of the eye.
irisThe muscle-filled ring that gives an eye its color. Its muscles widen the pupil in dim light and narrow it in bright light. A blue iris holds no blue pigment: it scatters light.
lensThe clear disk behind the pupil that changes shape. It does so to focus on objects that are close.
Show all 36 terms (30 more)
Parts of the eye, continued
optic nerveThe bundle of a million or so fibers leaving the eye. The count of fibers in one optic nerve runs from 770,000 to 1.7 million. They are the long fibers of nerve cells in the retina.
pupilThe round gateway that admits light to the eye. It is a hole in the iris. It looks black because the light that goes in is absorbed inside.
retinaThe eye's screen: the layer on which images land. It is a layer of light-sensitive tissue that lines the back of the eye.
rodsThe detectors that take over when the light is low. They pick out the shapes of things in black, white and gray.
scleraThe tough white coat of the eyeball. It covers nearly the whole surface of the eyeball. The six muscles that turn the eye are attached to it.
vitreous humorThe jelly that light crosses to reach the retina. It is a clear gel, and it fills the space behind the lens.
How the eye focuses light 12
apertureThe adjustable hole in a camera or an eye. The pupil is the aperture of the eye. It can narrow to about 2 millimeters across and widen to more than 8.
convex lensA lens thicker in the middle than at the edges. The eye and the camera both focus light through a convex lens. The lens of the eye is convex on both faces.
curvatureHow sharply a surface bends. The evenly curved surfaces of the cornea and the lens are what bend light onto the retina.
focal pointThe meeting place of rays after a lens bends them. In a well-focused eye the rays from each point of an object meet again at a point on the retina.
imageA likeness of a scene, formed by focused light. In the eye it falls on the retina. A camera forms the same kind of image on its sensor.
invertedFlipped top to bottom. The image that lands on the retina is inverted.
rayThe straight path of light, drawn as a line. Light travels in straight lines, so diagrams of the eye draw it as rays.
reflectTo throw back light instead of soaking it up. We see most objects by the light that reflects off them and travels to our eyes.
transparentSo clear that things beyond show sharply. A transparent material lets light through without scattering it. The cornea and the lens are transparent.
visible spectrumThe span of light that a human eye responds to. It runs from violet, at about 380 nanometers, to red, at about 700.
wavelengthThe property of light that the eye reads as color. It is the length of one complete wave. Violet has the shortest wavelength that we can see.
zonuleThe ring of fine fibers that holds the lens in place. Its fibers are attached to the capsule around the lens and hang the lens from the wall of the eye.
Signals, nerves and the brain 12
blind spotThe patch of retina that has no rods or cones. The optic nerve passes out of the eye there. The brain fills the gap with information from the other eye.
field of viewEverything that can be seen without moving the eyes. With both eyes it spans as much as 214 degrees from side to side. About 120 degrees in the middle is seen by both eyes at once.
hemisphereA brain half that handles the view on the other side. A deep groove divides the left hemisphere from the right, and a thick band of nerve fibers joins them.
optic chiasmThe place where the two optic nerves cross. It lies at the bottom of the brain. All vertebrates have an optic chiasm.
optic tractFibers that run from the crossing to the thalamus. It carries the optic nerve's signals onward and ends in the part of the thalamus called the lateral geniculate nucleus.
reflexA response the body makes without your deciding. The pupil narrowing in bright light is a reflex. Light shone into one eye makes both pupils narrow.
rhodopsinThe light-catching pigment inside the rods. Visual purple is its other name. Bright light bleaches it, and it takes about 30 minutes to be fully restored.
saccadeA quick jump of both eyes from one point to another. The word is French for jerk. Both eyes make the jump at the same moment.
sense organA body part built to detect the outside world. Light receptors in the eye and touch receptors in the skin both pick up signals from outside the body.
stimulusAnything that a sense organ can detect. For the eye the stimulus is light; for the skin it can be touch.
thalamusA hub deep in the brain that passes signals upward. Nerve fibers run from it to the cortex in all directions. There is a left thalamus and a right one.
visual cortexThe brain region that makes sense of what eyes send. It lies in the occipital lobe, at the rear of the head.
How this list was compiled: Term list chosen for this site on 2026-10-12. Each meaning is written in our own words and was checked that day against the article on the term in the English Wikipedia (https://en.wikipedia.org/), whose text is under the Creative Commons Attribution-ShareAlike license: Human eye, Cornea, Iris (anatomy), Pupil, Lens (vertebrate anatomy), Retina, Optic nerve, Sclera, Eyelid, Vitreous body, Ciliary muscle, Zonule of Zinn, Rod cell, Cone cell, Real image, Focus (optics), Ray (optics), Reflection (physics), Transparency and translucency, Aperture, Visible spectrum, Wavelength, Accommodation (vertebrate eye), Blind spot (vision), Visual cortex, Optic chiasm, Optic tract, Thalamus, Lateral geniculate nucleus, Cerebral hemisphere, Pupillary light reflex, Stimulus (physiology), Saccade and Rhodopsin. Sense organ, stimulus, field of view, inverted, aperture, curvature, zonule and saccade rest on their entries in Wiktionary, the free dictionary (https://en.wiktionary.org/). The path of light through the eye was checked against How the Eyes Work of the National Eye Institute (https://www.nei.nih.gov/learn-about-eye-health/healthy-vision/how-eyes-work); the sclera and its six muscles, the cornea and the lens, the zonules, the vitreous humor, the rods and the cones against Eye Anatomy: Parts of the Eye and How We See of the American Academy of Ophthalmology (https://www.aao.org/eye-health/anatomy/parts-of-eye); the visible spectrum against Visible Light of NASA Science (https://science.nasa.gov/ems/09_visiblelight/); the smooth muscle of the eye against Healthy Muscles Matter of the National Institute of Arthritis and Musculoskeletal and Skin Diseases (https://www.niams.nih.gov/health-topics/kids/healthy-muscles); and the iris, the upside-down image, the blind spot, blinking and reflected light against three BBC Bitesize pages (https://www.bbc.co.uk/bitesize/): How does the eye detect light?, Cameras and the human eye and The human eye and how it works. The fact after each meaning is from the same pages. Licence: own work
How it works
This human eye worksheet prints eye vocabulary to match: cornea, iris, pupil, lens, retina, optic nerve and six more parts stand beside their meanings in another order. The key is the last page. There is no eye to label.
Read the full guide
How the eye focuses light
Set opens on Parts of the eye. The second set has image, inverted, convex lens, focal point, ray, reflect, transparent, aperture, visible spectrum, wavelength, curvature and zonule.
Signals, nerves and the brain
The third set has blind spot, visual cortex, optic chiasm, optic tract, thalamus, hemisphere, sense organ, field of view, reflex, stimulus, saccade and rhodopsin.
Macula, fovea, choroid and conjunctiva are words on the eye word search, not terms here.
Questions and answers
How does the human eye work?
Light enters through the cornea and the pupil, and the lens focuses it on the retina. There the rods and cones turn it into electrical signals, which the optic nerve carries to the brain. The brain turns the signals into what you see.
Why is the image on the retina upside down?
Because the curved front of the eye bends the light as it goes in, which turns the picture over. The brain sorts out the signals and flips the image the right way up.
Why do we blink?
Blinking spreads tears over the eye, which keeps the cornea moist, and the blink reflex protects the eye from foreign bodies such as dust. The average person blinks 15 to 20 times a minute.