External Structure of the Eye

• External Structure of the Eyes

  • Upper eyelid
  • conjunctiva (covers sclera)
  • sclera
  • iris
  • pupil
  • lower eyelid
  • eyelashes
  • tear gland

  
• Sclera


  • white outer covering of the eyeball
  • continuous with the cornea
  • protects the eye from mechanical damage
• Conjunctiva


  • thin transparent mucous membrane covering the sclera
  • secretes mucus to keep the eyeball moist
• Eyelashes


  • shields the eyes from dust particles
• Tear gland


  • lies at the corner of the upper eyelid
  • secretes tears
  • tears wash away dust particles
  • tears keep the cornea moist for atmospheric oxygen to dissolve and diffuse into the cornea
  • tears lubricate the conjunctiva, reducing friction when the eyelids move
• Eyelids

  • protect the cornea from mechanical damage
  • squinting prevents too much light from entering the eye and damaging the retina
  • blinking spreads tears over the cornea and conjunctiva, and wipes dust particles off the cornea
• Iris


  • circular sheet of muscles that control the size of the pupil and how much light enters the eye
  • contains pigment that gives the eye colour
• Pupil


  • a hole in the centre of the iris to allow light to enter the eye