Biology - Eye

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  • Eye
    • Sensory organ with receptor cells (detect stimulus + sends impulse)
    • Sensitive to light intensity + colour (stimulus)
    • Structure
      • Scurla - tough, supporting outer layer. Protects eye.
      • cornea - transparent outer layer at front. Refracts (bends) light into eye
      • Pupil - dark hole where light enters
      • Iris - coloured part. Contains muscles to control pupil size (light)
      • Lens - focuses light onto retina (fatter - focus short. Thinner - focus long)
      • Ciliary muscle & suspensory ligament (smaller part) - control lens shape
      • Retina - layer of receptor cells at back. Detect stimulus & convert to impulses)
      • Optic nerve - carries impulses from retina to brain
    • Too much light damages retina
      • Musceles in iris control light intensity
        • Dim - Radial muscles contract, dilates pupil, more light
        • Bright - circular muscles contract, pupil constricts, less light
    • Object sends light rays out in all directions.
      • Light rays enter eye through cornea. As it does this, light refracts (converges)
        • It focuses on Retina, forming flipped image of object
    • Accommodation = changing lens shape to focus on objects
      • Focusing on near object:Light diverging more so need thicker lens to converge back to a point
        • Ciliary muscles contract. Sensory ligament loosens
      • Focusing on far objects: rays less diverged so lens refracts less then for close object
        • Cillar relax. Ligament contracts
    • Eye problems: lens doesn't focus light on retina
      • Myopia (short-sighted)
        • Far objects blurred. Eye too long / cornea too curved. Refracts too strongly so rays focus in front of retina
        • Concave (diverging lens).
          • Diverages light before enter eye.
      • Hyperopia (long-sighted)
        • Near objects blurred. eye ball too short / cornea too flat. Image formed behind retina instead of on retina
        • Convex (converging) lens
          • Converge before enter eye, so able to focus on retina
      • Eye contacts work same but are placed on eye
        • Risk: eye infection
      • Laser eye surgery. Reshapes cornea.
        • Permanent - risk
      • Replacement lens surgery. Lens placed permanently in eye
        • Surgery - risk


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