Knowledge centre

Explore how the eye works, how animals see the world, and why vision care matters. Educational information, not medical advice.

Anatomy of the human eye

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Tap a number or a name to learn about that part. Diagram is simplified.

Cornea

Clear dome at the front of the eye. It does most of the eye's focusing.

How many pixels is an eye?

Each human retina holds about 126 million light-sensing cells: roughly 120 million rods and 6 million cones. Yet each optic nerve carries only about a million nerve fibres, so the retina compresses the picture before it reaches the brain.

The eye is not a camera. Sharp detail comes from the tiny fovea at the centre of the retina, while the edges give a blurrier view that is tuned to movement. Slide to see how fewer or more pixels change an image.

Eyes of birds and animals

Pupil shape and eye position tell you how an animal lives. Illustrations are artistic and simplified.

Human

MammalRound pupil
  • About 126 million photoreceptors: roughly 120 million rods and 6 million cones.
  • Three types of cones give full colour vision.
  • The fovea gives sharp central detail.

Eagle and hawks

Bird of preyRound pupil, deep fovea
  • Vision several times sharper than a human's, so prey is spotted from very far away.
  • A deep fovea, and in some raptors a second one, gives telescope-like detail.
  • A bony brow shades the eye from glare.

Owl

BirdLarge round pupil
  • Tube-shaped eyes are fixed in the skull, so owls turn the whole head, up to about 270°.
  • Huge pupils gather light for night hunting.
  • Forward-facing eyes give good depth perception.

Birds in general

BirdRound pupil, UV vision
  • Many birds have four cone types, including one that sees ultraviolet light.
  • A comb-like pecten feeds the retina with nutrients.
  • A see-through third eyelid sweeps the eye clean.

Cat

MammalVertical slit
  • The slit can open very wide in dim light and close to a thin line in bright light.
  • A reflective layer, the tapetum lucidum, causes eyeshine at night.
  • Excellent at spotting movement.

Dog

MammalRound pupil
  • Wide field of view, up to about 240° depending on breed.
  • Sees mainly blue and yellow tones (two cone types).
  • A tapetum helps in dim light; sharpness is roughly 20/75 on the human chart.

Horse

MammalHorizontal oval
  • One of the largest eyes of any land mammal.
  • Side-set eyes give a view of nearly 350°, with small blind spots in front of the nose and directly behind.
  • Sees two main colour ranges (blue and green).

Goat and sheep

MammalHorizontal rectangle
  • The wide rectangular pupil gives a panoramic view of the ground and horizon.
  • Eyes rotate to keep the pupil level while the head lowers to graze.
  • Helps spot predators coming from the sides.

Octopus

MolluscW-shaped horizontal pupil
  • Its retina faces the light, so it has no blind spot.
  • The pupil keeps a horizontal slit even as the animal moves.
  • Sees mainly in one colour channel despite its colour-changing skin.

Chameleon

ReptileTiny pupil in a turret
  • Each cone-shaped turret moves independently, scanning almost 360°.
  • Both eyes lock forward to judge distance before the tongue shoots out.
  • The turret works like a pinhole to sharpen focus.

Dragonfly

InsectCompound eye
  • Each compound eye has up to about 30,000 tiny lenses, called facets.
  • Very quick at detecting motion, which helps catch flying prey.
  • Covers most of the head, giving an almost all-round view.

Caring for your eyes

Regular eye check-ups, UV protection and prompt treatment of cataract, glaucoma and dry eye help protect vision. See an eye doctor for any sudden change in sight.

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