The Eye

Only a small portion of each eye or eyeball is visible; the rest of the hollow, spherical, organ lies enclosed and protected by a cushion of fat within the bony orbit formed by certain skull bones. The eyeball has three layers. The outer fibrous layer consists of mostly of the tough, white, protective sclera; at the front of the eye it forms a clear window­­-the cornea-through which light is admitted. Extrinsic muscles attached to the sclera and orbit move the eyeball. The middle vascular layer forms the iris, the coloured part of the eye that surrounds pupil, as well as the suspensory ligaments that hold the focusing lens in place. The inner layer, the retina, contains over 70 percent of the body’s sensory receptors. These photoreceptors detect the patterns produced by light reflected from objects outside the body and send messages to the brain.

Key:

1. Superior rectus muscle
2. Lateral rectus muscle
3. Optic nerve
4. Inferior rectus muscle
5. Eyeball
6. Cornea
7. Sclera
8. Inferior oblique muscle
9. Skull

Vision and the visual cortex

The conscious perception of visual images-seeing-happens in the primary visual cortex located in the optical lobe of the left and right cerebral hemispheres. Nerve fibres from the retina, the light-detecting layer inside the eye, travel along the optic nerves to the primary visual areas. En route, certain fibres cross over so that the left primary visual area receives visual images from the right side of the object in view, and the right primary visual area receives visual images from the left side. Different centres within each primary visual cortex process information about the shape, colour, movement, and location of the object being looked at. Because each primary visual area receives a slightly different view of the object, from both area is “pooled” to produce binocular or three-dimensional vision that enables a person to perceive depth. Surrounding the primary visual areas are the visual association areas. Here, incoming visual information is compared to previous visual experiences so that, for example, a person can recognize a familiar face or object.

I hope you enjoyed and if you like this article you may also want to check my other articles.