Eye Notes
Structure of the Eye
Cornea – transparent front layer; refracts light and protects the eye.
Aqueous humour – nourishes eye and maintains pressure.
Iris – controls pupil size.
Pupil – opening that lets light enter.
Lens – focuses light on retina.
Ciliary muscles – change lens shape.
Suspensory ligaments – hold lens.
Vitreous humour – jelly maintaining eye shape.
Retina – light-sensitive layer with rods and cones.
Fovea – sharpest vision.
Optic nerve – carries impulses to brain.
Sclera – tough white outer coat.
Choroid – nourishes retina and absorbs stray light.
Functions
Cornea refracts light; Iris controls light; Pupil admits light; Lens focuses; Retina converts light to
impulses; Rods see in dim light; Cones detect colour; Optic nerve carries impulses; Vitreous and
aqueous humours support and nourish the eye.
Accommodation
Distant objects: ciliary muscles relax, ligaments tighten, lens thin, image focused on retina.
Near objects: ciliary muscles contract, ligaments slacken, lens thick, image focused on retina.
Eye Defects
Myopia: image in front of retina; corrected by concave lens.
Hyperopia: image behind retina; corrected by convex lens.
Astigmatism: irregular cornea/lens; corrected by cylindrical lenses.
Presbyopia: ageing lens loses elasticity; corrected by reading glasses, bifocals or progressives.