| Structure | Position | Function |
|---|---|---|
| Outer layer | ||
| Sclera | Outer layer of the eye | Protects the eyeball |
| Cornea | Transparent dome of the tissue forming the outer layer at the front of the eye | Refracts light, focusing it on the retina |
| Middle layer | ||
| Choroid | Pigmented layer containing blood vessels | Absorbs stray light; delivers nutrients and oxygen to tissues of eye |
| Ciliary body | Encircles lens; contains the ciliary muscles | Controls shape of lens; secretes aqueous humor |
| Iris | Colored part of the eye | Regulates the amount of light entering the eye through the pupil |
| Pupil | Opening at the center of the iris | Opening for incoming light |
| Inner layer | ||
| Retina | Layer of tissue that contains the photoreceptors (rods and cones); also contains bipolar and ganglion cells involved in retinal processing | Receives light and generates neural messages |
| Rods | Photoreceptor | Responsible for black and white vision and vision in dim light |
| Cones | Photoreceptor | Responsible for color vision and visual acuity |
| Fovea | Small pit in the retina that has high concentration of cones | Provides detailed color vision |
| Other structures of the eye | ||
| Lens | Transparent, semispherical body of tissue behind the iris and pupil | Fine focusing of light onto retina |
| Aqueous humor | Clear fluid found between the cornea and the lens | Refracts light and helps maintain shape of the eyeball |
| Vitreous humor | Gelatinous substance found within the chamber behind the lens | Refracts light and helps maintain shape of the eyeball |
| Optic nerve | Group of axons from the eye to the brain | Transmits impulses from the retina to the brain |