Visual fields Flashcards
(15 cards)
Why do we need VFA?
- To detect/screen pathologies
- Diagnose pathology
- Monitor pathology
- Assessing funtional vision (should those with visual defect be allowed to drive?
What is a visual field?
All the space that an eye can see at a given instant in time.
How is visual field quantified?
Quantified with:
1. contrast
2. degrees
3. ability to detect flicker
What determines your visual field?
Monocularly= extent of photoreceptors at retina. And the angle of incidence and refraction at ocular media
Binocularly= placement of eyes in skull
What is the size of normal visual field?
Temporal = 95degs (slightly behind because of refraction of light by media)
Nasal = 60 degs (due to nose getting in the way)
Superior = 65 degs
Inferior = 75 degs
Draw the sensitivity profile
Y axis= sensitivity
X axis = eccentricity
scotopic two peaks
mesopic
photopic = traquairs hill of vision
What is the sensitivity profile detemined by?
- Distribution of photoreceptors
- Distribution of retinal ganglion cells
Name and describe all the scotomas
- Positive scotoma = dark/grey/white patch seen by Px
- Negative scotoma = brains fills in, px doesnt notice
- Absolute scotoma = all retinal sensitivity is lost in that area
- Relative scotoma = reduced sensitivity in that area
Describe the blood supply to the eye
No blood supply to foveola
inner 2/3rds of retina supplied by retinal arteries (retinal vasculature)
Outer 1/3rd of retina supplied by short/long posterior ciliary arteries (choroidal vasculature)
Draw the circle of willis
- Anterior cerebral arteries
- Anterior communicating artery
- Ophthalmic arteries
- Internal carotid artery
- Posterior cerebral arteries
- Posterior communicating artery
- Basilar artery
Describe the nerves at retina
arcuate fibres
radial fibres
no ganglion cells cross the raphae
What caution to take for glaucoma defects?
- Could be mistaken for angioscotoma = two big blood vessels cross
- Non linear progress = defect looks as though it has improved but it actually hasn’t
Name the non automated perimetry methods
- Gross fields
- Confrontation tests
- Amsler grid
- Bjerrum screen
- Goldmann perimeter
- Frequency doubling perimetry
What is weber’s law of contrast?
Constant =
Difference in luminance/Background luminance
What are the sections on visual field printout?
- Test selection and general info
- Reliability
- Numeric results
- Greyscale results
- Total deviation
- Pattern deviation
- Glaucoma hemifield test
- Global indices
- Probablity symbols
- Gaze graph
