CorneaThe clear front of the eye. A cow's is thicker than a horse's.
IrisThe colored ring that makes the pupil wider or narrower. A cow's is very dark.
PupilThe opening that lets light in. A cow's is a wide horizontal oval.
LensSits behind the iris and focuses light onto the retina.
RetinaThe light-sensing layer lining the eye's rear.
Tapetum lucidumA shiny layer that reflects light back through the retina. It makes eyes glow at night.
Optic nerveCarries signals from the retina to the brain.
The wall and the back: 6 3
ScleraThe tough white outer wall of the eyeball.
ChoroidThe dark layer of blood vessels between the sclera and retina.
Optic discWhere the optic nerve leaves the retina; it has no light sensors.
Inside the eye: 4 3
Aqueous humorWatery fluid filling the space behind the cornea.
Vitreous humorClear jelly filling the eyeball behind the lens. A cow's is firmer than a horse's.
Ciliary bodyHolds the lens by fine fibres and makes the aqueous humor.
How this list was compiled: Read 2026-09-26. Sisson, The Anatomy of the Domestic Animals (1914), https://archive.org/details/anatomyofdomesti00siss : the eye (cornea, sclera, chorioid and its tapetum, ciliary body, iris, pupil, lens, aqueous humor, vitreous body, retina, optic papilla, optic nerve) and the eye of the ox. Merck Veterinary Manual, Eye structure and function in horses, https://www.merckvetmanual.com/horse-owners/eye-disorders-of-horses/eye-structure-and-function-in-horses . Wikipedia: Eye, https://en.wikipedia.org/wiki/Eye ; Tapetum lucidum, https://en.wikipedia.org/wiki/Tapetum_lucidum ; Optic disc, https://en.wikipedia.org/wiki/Optic_disc (no rods or cones: a blind spot); Ciliary body, https://en.wikipedia.org/wiki/Ciliary_body (attached to the lens by zonule fibres; its epithelium makes the aqueous humor). Licence: own work
The drawing: Drawn for this site by script, 2026-09-26. Own work, nothing traced. Licence: own work
How it works
The parts of a cow's eye, the one most lab classes study, on two drawings: the eyeball cut across, and the eye from the front. Start with the 7 main parts, then the front, the wall and the inside.
Read the full guide
Front to back
Light passes the clear cornea and the aqueous humor, then the pupil in the dark iris, then the lens, held by the ciliary body. It crosses the vitreous humor, a clear jelly, to the retina lining the back.
The wall
The wall has three layers: the tough white sclera outside, the dark choroid in the middle, and the retina inside. The optic nerve leaves at the optic disc. In the choroid, the tapetum lucidum shines blue and green.
The tapetum lucidum is what makes a cow's eyes glow in headlights; people do not have one.
Questions and answers
What is the shiny part inside a cow's eye?
The tapetum lucidum, a reflective layer in the choroid at the back of the eye. In a cow it shines from green to deep blue, and it helps the cow see in dim light.
What shape is a cow's pupil?
A wide horizontal oval, unlike the round pupil of a human eye.
What is the blind spot in a cow's eye?
The optic disc, where the optic nerve leaves the retina. It has no light-sensing cells, so it cannot see.