Docstoc

Adequate Illumination

Document Sample
Adequate Illumination Powered By Docstoc
					             Adequate Illumination
•   Retina must be adequately diffused with light to capture an image
     •   Just like film in a camera-too little or too much light affects quality of the
         picture
•   Change in pupillary function will also affect amount of illumination retina
    receives
     •   Affects tolerance to light
           • May become photophobia-unable to tolerate light
           • May experience more problems with glare
           • May be unable to function in daylight
•   Opacity in intervening structures also affects amount of illumination
    retina receives
     •   Cartaract and corneal and vitreal opacities can affect illumination
Ability of Retina to Capture Image
 • Retinal function can be affected by injury,
   vascular disruption or disease
 • Damaged retina creates blind spot in vision
   • Known as a visual field loss (VFD) or as a
     scotoma if it occurs in the central visual field
 • Performance limitations depend on area of
   retina damaged
   • Peripheral vs. central visual field
      • Each brings it’s own set of unique challenges
Damage to Central Retina:
   Macula and Fovea

  Creates a central visual field
             deficit
         Macular Scotoma
• Area of reduced light sensitivity within
  central 20 degrees of the visual field
             Macular Scotoma
• Occurs with retinal diseases
• Affects ability to
   • See small details
   • Discriminate contrast
   • Discriminate color
• Primary pathology dealt with in patients with low
  vision
   • 83% of patients referred for low vision services found to
     have dense macular scotomas regardless of disease
    Learning about macular scotoma has been a
    slow and difficult process
•   Too small to pick up with standard
    testing
•   Understanding of scotomas occurred
    after development of the scanning laser
    ophthalmoscope (SLO)
•   SLO provides very precise imaging of
    foveal/macular area
     • Can image scotomas as small as 5
         degrees
• SLO has contributed significantly to
  science of low vision                       Scanning Laser Ophthalmoscope
          Central Scotoma
• Scotoma impinges
  on and involves the
  fovea
  • ds = dense scotoma                        Fovea

                                                         Optic disc




                         SLO image of the right eye showing
                         a central scotoma starting to impinge
                         on the fovea
      Para-central Scotoma
• Within the central 20
  degrees of the field
  but not involving the     Central scotoma

  fovea


                          Para-central scotoma
            Ring Scotoma
• Surrounds the fovea
  on 4 sides            Dense scotoma



                           Fovea
Scotomas may vary in density
• Dense (d/s green)
  • No response to light


• Relative/Threshold       Fovea/fixation
  (t/s orange)
  • Responds to light if
    bright enough

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:4
posted:1/23/2012
language:
pages:10