- Rods respond to low intensity light; cones, which require high intensity light, identify colour.
- The blind spot is where the optic nerve attaches to the retina; no rods or cones are present in this area, so there’s an absence of photosensitive cells
- Ciliary muscles change the shape of the lens. A thicker lens permits the greater bending of light for viewing near objects, while a more flattened lens is used to view distant objects.
- Accommodation: adjustments made by the lens and pupil of the eye for near and distant objects. With age, the layers of transparent protein covering the lens increase throughout your life, making the lens harder. As the lens gets harder, it loses flexability.
| Structure | Function |
| Sclera | Supports and protects delicate photocells |
| Cornea | Refracts light towards pupil |
| Aqueous Humour | Supplies cornea with nutrients and refracts light |
| Choroid Layer | Contains pigments that prevent scattering of light in the eye by absorbing stray light; also contains blood vessels |
| Iris | Regulates the amount of light entering the eye |
| Pupil | The opening in the iris that allows light into the eye |
| Lens | Focuses the image on the retina |
| Ciliary muscles | Change the shape of the lens |
| Vitreous humour | Maintains the shape of the eyeball and permits light transmission to the retina |
| Retina | Contains the photo receptors |
| Fovea Centalis | Most light sensitive area of the retina; contains only cones |
| Vision Defect | Cause | Treatment |
| Glaucoma | Build up of aqueous humour in the anterior chamber of the eye | |
| Cataract | When the lens or cornea become opaque, preventing light from passing through | |
| Astigmatism | Abnormal curvature of surface of the lens or cornea | Glasses that contain an astigmatic lens |
| Nearsightedness (myopia) | Condition that occurs when the image is focused in front of the retina | Glasses that contain concave lenses |
| Farsightedness (hyperopia) | Eyeball is too short
Occurs when the image is focused behind the retina |
Glasses that have a convex lens |
