Light At Work

• Cornea


  The outer thin, transparent membrane of the eyeball that covers the iris, pupil, and anterior chamber
• Conjunctiva


  The thin, transparent tissue that lines the inner surfaces of the eyelids and the outer surface of the eyeball
• Sclera


  The visible white area of the eye that provides structure, protection, and strength to the eyeball
• Pupil


  The black circle in the middle of the eye that is an opening through which light enters the inner portion of the eye
• Iris


  The colored circle of the eye that regulates the size of the pupil through the contraction or relaxation of its muscles
• Crystalline lens


  The clear convex structure behind the pupil that can focus on objects at different distances by changing its shape
• Ciliary muscles


  Attached to the crystalline lens and responsible for changing the shape of the lens when focusing on objects at different distances
• Retina


  The inner surface of the eye where the image of an object is formed
• Fovea


  The region of most distinct vision in the retina
• Optic nerve


  Carries images from the retina to the brain
• Choroid


  The layer between the retina and sclera composed of blood vessels and connective tissue that nourishes the back of the eye
• Aqueous humor


  The gellike fluid between the cornea and lens responsible for giving the eye its near perfect spherical shape and belonging to the refractive system
• Vitreous humor


  The gellike fluid on the other side of the lens also responsible for giving the eye its shape and belonging to the refractive system
• Braille


  A system using varied arrangements of raised dots representing the letters of the alphabet, used by blind people to read and write by touch
• How vision works

  1. Light enters the eye through the cornea

  2. Light passes through the pupil

  3. Light is focused by the crystalline lens

  4. Image is formed on the retina

  5. Image is relayed to the brain by the optic nerve
• Near point


  The closest distance at which an object can be seen clearly by the eye
• Far point


  The farthest distance at which an object can be seen clearly by the eye
• Common vision problems

  • Myopia
  • Hyperopia
  • Presbyopia
  • Astigmatism
• Myopia


  Nearsightedness - can see nearby objects clearly but distant objects are blurry
• Hyperopia


  Farsightedness - can see distant objects but cannot focus clearly on nearby objects
• Presbyopia


  Age-related vision problem where the crystalline lens hardens and the ciliary muscles become less flexible, making it difficult to focus on nearby objects
• Astigmatism


  Inability to focus simultaneously on horizontal and vertical lines due to irregular cornea shape or unequal curvature
• Diopter


  The unit of power of a corrective lens, equal to the reciprocal of the focal length in meters
• Correcting myopia


  1. Use a diverging (concave) lens

  2. Lens causes light to bend slightly before entering the eye so image is formed on the retina
• Correcting hyperopia


  1. Use a converging (convex) lens

  2. Lens focuses light so image is formed on the retina
• Presbyopia cannot be prevented, it is a normal consequence of growing old
• Bifocal lens


  Has an upper half for normal viewing and a lower half for reading
• Progressive lens


  No-line bifocal that eliminates the "split-image effect"
• Cylindrical lens


  Used to correct astigmatism by focusing light properly
• Keratectomy is a type of eye surgery
• Astigmatism


  A person suffering from astigmatism cannot focus simultaneously on horizontal and vertical lines
• Astigmatism


  • Caused by the cornea's irregular shape or unequal curvature
  • Corrected by a cylindrical lens
• Camera obscura


  A darkened box with a single small opening and a white projection screen, used to project an inverted real image
• Camera


  A mechanical eye, similar to the human eye in terms of essential structures and function
• Digital camera


  • Uses image sensor (CCD or CMOS) to detect and convert light into electrical charges
  • Equipped with LCD screen
• Magnifying glass


  A converging lens that produces a virtual, upright, and enlarged image of an object placed at a distance less than its focal length
• Magnification


  Absolute value of the ratio of the image distance to the object distance from the lens
• Refracting telescope


  • Uses lenses for objective and eyepiece
  • Produces real, inverted, and smaller first image
  • Eyepiece acts as a magnifying glass to produce a magnified virtual final image at infinity
• Reflecting telescope


  Uses a concave mirror as the objective instead of a lens