Define sensation and elucidate the processes of vision with the structure of the eye.

Sensation refers to the process of detecting and interpreting stimuli from the environment through the senses. The sensation is a fundamental aspect of human experience and plays a crucial role in our ability to perceive and interact with the world around us.

Vision is the sense that allows us to see and interpret the visual world. It is one of the most important senses, as it enables us to gather information about our surroundings, navigate through space, and communicate with others.

The process of vision begins when light waves enter the eye and are focused by the cornea and lens onto the retina, a layer of light-sensitive cells at the back of the eye. The retina contains two types of cells called rods and cones, which are responsible for detecting light and colour, respectively. When light hits these cells, it triggers a chemical reaction that converts the light energy into electrical signals.

These electrical signals are transmitted through the optic nerve to the brain, where they are interpreted as visual images. The brain processes this information and uses it to construct a mental representation of the visual world.

The structure of the eye plays a critical role in the process of vision. The eye is a complex organ that is made up of several different parts, each of which performs a specific function. The main parts of the eye include:

1. Cornea: The cornea is the clear, curved surface at the front of the eye that helps to focus light onto the retina.
2. Iris: The iris is the coloured part of the eye that surrounds the pupil. It controls the amount of light that enters the eye by adjusting the size of the pupil.
3. Pupil: The pupil is the small, circular opening in the centre of the iris that allows light to enter the eye.
4. Lens: The lens is a clear, flexible structure located behind the pupil that helps to focus light onto the retina.
5. Retina: The retina is a layer of light-sensitive cells at the back of the eye that converts light energy into electrical signals.
6. Optic nerve: The optic nerve is a bundle of nerve fibres that carries electrical signals from the retina to the brain.
7. Brain: The brain processes the electrical signals from the retina and interprets them as visual images.