structure of eye

• sclera

  tough white outer covering of eyeball

  protects eyeball from mechanical damage

  is covered by a transparent layer (conjunctiva)
• rectus muscle

  contract and relax to control movement of eyeball
• cornea

  dome-shaped transparent layer

  continuous with the sclera

  cause greatest refraction of light into eye
• aqueous humour

  transparent, watery fluid

  keeps front of eyeball firm

  helps refract light into pupil
• lens

  transparent, circular & biconvex structure

  elastic and change thickness to focus light onto retina
• retina

  light-sensitive layer

  contains photoreceptors
• blind spot

  region where the optic nerve leaves the eye
• optic nerve

  transmits nerve impulses to the brain

  photoreceptors stimulated
• fovea

  small yellow depression

  where images are normally focused

  contains greatest concentration of photoreceptors
• suspensory ligaments

  connective tissue that attaches the edge of the lens to ciliary body
• ciliary body

  contains ciliary muscles

  which controls curvature or thickness of the lens
• choroid

  middle layer of eyeball

  2 functions:

  1. pigmented black to prevent internal reflection of light
  2. contains blood vessels that bring oxygen and nutrients to eyeball & remove metabolic waste products
• virtuous humour

  transparent, jelly-like substance

  keeps eyeball firm

  helps refract light onto retina
• conjunctiva

  thin transparent membrane covering sclera in front

  secretes mucus to keep front of eyeball moist
• eyelashes

  shield eye from dust particles
• tear gland

  secretes tears that:

  1. wash away dust particles
  2. keep cornea moist for dissolved oxygen to diffuse into cornea
  3. lubricate conjunctiva to reduce friction
• eyelids

  protects cornea from mechanical damage
• iris

  comprise circular & radial muscles working antagonistically

  control size of pupil

  contains pigment that gives eye its colour
• pupil

  a hole that allows light to enter eye