parts of the eyes

• Visual perception starts at the eye, where light is

  received, transduced then sent to the brain for

  interpretation
• Cornea: a transparent, convex-shaped

  (curved outwards) covering which protects

  the eye and helps to focus light rays onto

  the retina at the back of the eye
• Aqueous humour: a watery fluid which helps

  to maintain the shape of the eyeball and

  provides nutrients and oxygen to the eye, as

  well as carrying away waste products.
• Pupil: an opening in the iris that helps to

  control the amount of light entering the eye.
• Iris: surrounds the pupil, and is the

  coloured part of the eye.

  The iris is a ring of muscles which

  expand or contract to change the size

  of the pupil and control the amount of

  light entering the eye.
• Lens: a transparent, flexible, convex structure

  located immediately behind the pupil.

  It plays a major role in focusing light onto the

  retina for processing. To do this, it adjusts its

  shape according to the distance of the object

  being viewed.
• Ciliary muscles are responsible for the lens

  being able to change shape.

  They are attached to each end of the lens.

  These muscles expand and contract, enabling

  the lens to automatically bulge to focus

  nearby objects onto the retina and flatten to

  focus distant objects onto the retina.
• Vitreous humour: a jelly-like substance which

  helps to maintain the shape of the eyeball

  and also helps focus light.
• Retina: receives and absorbs light, and also

  processes images.

  The image focused onto the retina is an

  inverted (upside-down) and reversed

  (back-to-front) image of the object being

  viewed.

  When received at the brain, it is rearranged

  so that we can perceive whatever we are

  looking at as it is in reality.
• There are two types of photoreceptors located in the retina:

  • Rods, which are photoreceptors that allow someone to see in low levels of light.

  • Cones, which are photoreceptors that allow someone to see colour and fine details in well-lit conditions.
• Optic nerve: carries the visual information from the

  retina to the primary visual cortex.
• A receptive field is the area of space in which a receptor can

  respond to a stimulus. For example, when you look directly in

  front of you, everything you see is the receptive field of your

  eyes.