Vision

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Author:
DesLee26
ID:
209538
Filename:
Vision
Updated:
2013-04-08 17:13:16
Tags:
BIO 220
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HQII
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  1. What is hyperopia?
    • farsightedness
    • distance vision is blurred when light rays focus behind the retina
  2. How to correct hyperopia
    correction with a plus lens allows light to once again focus on the retina
  3. What is myopia?
    • nearsightedness
    • distant vision is blurred when light rays from distant objects come to focus in front of the retina
  4. How to correct myopia
    correction with a minus lens allows light to once again focus on the retina
  5. What are the three tunics?
    • eye divided into 3 layers/ coats
    • fibrous
    • vascular
    • sensory tunic (retina)
  6. Fibrous tunic has __ different regions. What are they?
    • two 
    • sclera
    • cornea
  7. slcera
    • means hard
    • white
    • forms posterior portion and majority (85%) of fibrous tunic
    • anterior part covered by simple squamous epithelium: conjunctiva
    • very high in collagen (dense connective regular tissue that is linear to give a crystalline and clear tendency
  8. cornea
    • anterior portion of fibrous tunic (approx. 15%)
    • regular arrangement of collagen fibers make it crystal clear
    • many pain fibers and fibers associated with reflex blinking and lacrimal secretion
    • no vessels, derives nutrients from aqueous humor
  9. What are the parts of the vascular tunic?
    • choroid
    • ciliary body
    • iris
  10. choroid
    • highly vascular, dark brown (contains much melanin) pigmented
    • continuous anteriorly with ciliary body and iris
    • has tapedum: in nocturnal animals only [must be able to see at night]= reflective surface
    • - reason: minimum amount of light will reflect around the eye to allow it to see
    • humans have no tapedum; they have a choroid
  11. ciliary body
    • contains bundles of smooth muscles (ciliary muscles)
    • suspensory ligaments: connect ciliary body to lens
    • tension on ligaments causes lens to flatten
    • When ligaments relax, lens get thicker due to internal elasticity
    • Ciliary process: highly vascularized portion of ciliary body that produces aqueous humor; has blood vessels
    • makes fluid in front of lens; aqueous humor
  12. Iris
    • visible colored part of the eye (gives the color) pigmented (melanin)
    • located between lens and cornea
    • forms central opening, the pupil, through which light enters eye
    • acts as reflexively activated diaphragm
    • in bright light, smooth muscles of iris contract causing pupil to constrict, and vice versa
    • constriction/ dilation also controlled by sympathetic (dilation) and parasympathetic (constriction) fibers
  13. canal of schlem
    drains humor
  14. Explain the tapedum.
    • similar to the choroid of nocturnal animals only; must be able to see at night; acts as reflective surface
    • in humans, we have the choroid
    • the reason a minimum amount of light will reflect around the eye to allow it to see
  15. What are pupils?
    What is red eye?
    • black holes since the light that goes in can't come back out.
    • light reflecting off of the capillaries; there is so much light that the choroid can't absorb
  16. How many layers of the retina are there? What are the most important three?
    • ganglioin cell layer (has ganglion cells)
    • bipolar cell layer (bipolar, horizontal, and amacrine cells)
    • rods and cones cell layer (photoreceptors)
  17. What is the third tunic? What does it contain?
    • sensory tunic (retina)
    • neural layer
    • optic disk
    • fovia
  18. Neural (nervous) layer
    • direct mediator of vision
    • transparent
    • outpocketing of the brain
    • Has five cell types: photoreceptors, bipolar cells, ganglion cells, horizontal cells, amacrine cells
  19. Optic disc (optic nerve head)
    • small circular area in medial retina where the optic nerve exits the eye
    • no photoreceptor cell present in this part of the retina (no rods or cones)
    • functionally, it is the "blind spot"
  20. Fovia
    • focal point for light on the retina. Center of the visual field
    • point of greatest visual acuity (sharpest vision)
    • light passes directly to photoreceptors since all other cells displaced, i.e., bipolar and ganglion cells off to side
    • site of greatest cone concentration (nothing but cones)
  21. Refraction by the Cornea
    parallel light rayes from object greater than 20 ft.
  22. Accommodation by the Lens
    • accommodation= lens changes shape for near vision
    • divergent light rays
    • ciliary muscles (from the ciliary body)contract to relieve tension on lens (lens get fatter, thickening by its own elasticity)
    • incraesed curvature increases refractive power
  23. What does the cornea function for?
    objects greater thantwenty feet away
  24. What does the lens function for?
    objects nearer than twenty feet
  25. Normal vs. Abnormal:
    • hyperopia
    • presbyopia
    • myopia
    • astigmatism
  26. Hyperopia (farsighted)
    eyeball too short; light focuses behind retina
  27. Eumotropia
    normal vision
  28. presbyopia
    hardening of lens that accompanies aging; lens  unable to flatten sufficiently during relaxation adn unable to fatten sufficiently during accommodation; due to cross-linking of collagen fibers; loses elasticity
  29. astigmatism
    irregularities in the curvature of the cornea or lens that produce different amounts of refraction
  30. Snellen eye chart
    20/20 vision: numer of feet required by a gien individual to discriminate characters on a specific line in the eye chart over the number of feet average perage person requires to view the same line
  31. photoreception
    • retinal
    • rhodopsin
    • bleaching
  32. retinal
    • light absorbing molecule; synthesized from vitamin A (retinol)
    • cis (bent), but becomes trans when the light hits it
  33. Rhodopsin
    • opsin (protein that starts the response) and retinal; red pigment called "visual purple" important for vision in dim light
    • also called visual purple
  34. bleaching
    • deactivation of rhodopsin by bright light; separation into opsin and retinal 
    • (rods are more sensitive to light than cones)
  35. Rods are for __. Rods are not really used in daylight because what? 
    When there is not enough light for cones and rods are inactive, what?
    • grey (sensitive)
    • light is so intense
    • the rods kick in; night vision
  36. Rods and Cones
    photoreceptors of the vertebrate eye
  37. Rods
    more sensitive to light than cones, but don't distinguish color
  38. Cones
    responsible for daytime color vision; visual acuity, best visual discrimination for visual acuity
  39. The __ has nothing but __ because of the __.
    • fovia (pit/ indentation)
    • cones
    • visual acuity
  40. __ subclasses of cones, each with its own type of __ associated with __ to form visual pigments: 
    __(3)__
    • three
    • opsin
    • retinal
    • red, green, blue
  41. What is the mechanism?
    • light causes shape change in retinal
    • triggers chain of metabolic events that decrease signal to cells with which photoreceptor cells synapse
    • it is a decrease in the chemical signal that serves as the message
    • rods and cones synapse with bipolar neurons, which synapse with ganglion cells
  42. Invertebrate eyes:
    • eye cup of planarians
    • compound eye of invertebrates
  43. Explain the eye cup of planarians.
    • simple light receptor that responds to light intensity and direction without forming an image
    • planaria are negative photropic to avoid predation
  44. Compound eye of invertebrates
    • e.g.: insects, crustaceans, and some polychaete
    • Thousands of light detectors called ommatidia, each with its own cornea and lens
    • results in mosaic image
  45. The lens is a __ into what?
    • divider
    • space in front: anterior segment
    • space behind: posterior segment
  46. anterior chamber
    subdivision of the anterior segment in front of the iris and behind the cornea
  47. posterior chamber
    behind iris and in front of lens
  48. cones are __ and need more __.
    less sensitive (need more light)
  49. The vitreous humor is __.
    jelly-like

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