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clinical skills > Visual Field Analysis ? > Flashcards

Visual Field Analysis ? Flashcards

1
Q

what personal details should you?

A 
..Is it the correct patient
..Record ID number 
..name 
..DOB (Age) 
..Refractive Error

Is the data correct
..Date of test
..correct eye

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2
Q

How is the reliability criteria classified?

A

False positive
False negatives
Fixation losses

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3
Q

When is the data unreliable?

A

False positive >33%
False Negative >33%
Fixation losses >20%

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4
Q

What does False positive mean?

A

Patient says they can see a light when no light is shown or responds faster than usual humanly possible

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5
Q

What does False negative mean?

A

Patient says they cant see a light when they are shown a brighter light in a location where they said they could see it before

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6
Q

What does fixation loss mean?

A

Patient responds to a light which is shown in their blind spot

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7
Q

What does data representation have?

A 
Numeric printout 
Greyscale
Global visual field indices
Total and pattern deviation maps
Probability analysis
Glaucoma analysis
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8
Q

What does the numeric printout show?

A

Numeric representation of the threshold sensitivity. Higher the number the higher the threshold sensitivity

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9
Q

what does 0dB mean?

A

Just able to see the perimeters brightest max light

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10
Q

What does <0dB mean ?

A

Not able to see detect the perimeters brightest light cannot see anything then

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11
Q

what do the brackets mean in numeric printout?

A

Threshold measured twice

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12
Q

What does the grey scale show?

A

the grey scale is a graphical representation of the numeric printout ?

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13
Q

what does threshold sensitivity change with?

A

age

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14
Q

what happens as we get older?

A

decline in sensitivity?

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15
Q

how much sensitivity changes with age?

A

0.7 dB per decade

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16
Q

What is relative visual field sensitivity?

A

The difference between the measured visual field sensitivity and the age-corrected normal visual field sensitivity. This is also called the Total Deviation Decibel map

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17
Q

What does the Total deviation decibel map mean?

A

Total deviation decibel map= patients measured threshold sensitivity - the normal threshold sensitivity for their age at each test location

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18
Q

what does the negative numbers mean?

A

the number of dB less than they should have seen for their age

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19
Q

what are confidence intervals?

A

If the measured sensitivity is outside the confidence interval it is registered as abnormal and a probability level is assigned.

20
Q

what does grey probability symbols mean?

A

the darker the more genuine pathology there is

21
Q

what does localised visual field loss do?

A

Age matched normal field

measured field

22
Q

what does cataract show?

A

a cataract of 20dB will register with the darkest probability symbol and mask any localised loss.

23
Q

what does the diffuse lost do?

A

diffuse loss hides the localised lost and hides the pathology

24
Q

what does the pattern deviation probability map show in cataract?

A

Pattern deviation plots exposes localised loss by adjusting the general height of the hill

25
Q

What does the global visual field indices do?

A

Global visual field indices summarises the information about one aspect of the entire test.

26
Q

what type of three global indices are there?

A

Diffuse loss
Focal loss
variability

27
Q

What is Mean Deviation (MD)?

A

average of the total deviation values?

28
Q

When is MD abnormal?

A

if the mean deviation is greater than -2.00dB

29
Q

when do you increase MD?

A

in the presence of cataract and or large areas of focal loss

30
Q

What is pattern standard deviation PSD?

A

the standard deviation around the mean of the total deviation

31
Q

What are PSD sensitive to?

A

non uniformity in the visual field

32
Q

when is PSD abnormal ?

A

abnormal when value greater than +2.00dB

33
Q

what is advantage of global indices?

A

Give a single measure about the state of the visual field

can be used to monitor visual field change over time(Progression)

34
Q

What is the disadvantage of global indices?

A

There is loss in spatial information

35
Q

What is glaucoma hemifield test?

A

visual field sectors corresponding to the retinal nerve fibre arrangement in the upper hemifield are comp[ared for asymmetry with their mirror image sectors in lower hemifield

36
Q

how does glaucoma hemifield classify pathology?

A 
within normal limits
outside normal limits 
borderline
general reduction in sensitivity 
abnormally high sensitivity
37
Q

what might artificially affect visual field plot?

A

mistakes are often made on the first examination
repeat fields at a later date
repeat at least once before considering referral
repeating on the same day would be affected by fatigue

38
Q

what is the affect of fatique on VF ?

A

Clover leaf pattern on grey scale resulting from fatigue
fixation losses
increase in false negative

39
Q

what might happen in fatigue effect?

A

increase in false +ve and false -ve responses

  • fixation losses
  • contraction opf the visual field due to droopy eyelids
40
Q

How can you reduce the fatigue affect?

A

talk to the patient

encourage the patient

41
Q

what happens to fatigue effect in pathology?

A

effects maybe exaggerated in patients with pathology

42
Q

what other contraction due to external factors are there?

A
  • droopy eyelids-maybe fatigue related
  • heavy facial features
  • spectacle rim
  • lens holder
  • hair
  • poor positioning occluder
43
Q

what happens in functional or hysterical field loss?

A

Failure of the patient to respond to visible stimuli

typically produces variable responses

Kinetic perimetry- peripheral isopter tends to decrease in size throughout testing
-spiral or star shaped isopter

44
Q

Give examples of functional loss?

A

> Produce falsely low sensitive values at various location
>high false negative rate
>High spatial frequency value
>High no at the primary seed points give distinct clover shaped pattern
>long test duration particularly with SITA

45
Q

What is true pathology of cataract?

A

General reduction in sensitivity
>HIGH mean deviation
>LOW pattern standard deviation/CPSD
>large no of significant pionts on Total deviation map

46
Q

What is true pathology of early Glaucoma?

A

> nasal step is an early vf defect in glaucoma
note that MD and PSD are low
significant total and pattern deviation maps

47
Q

what is true pathology of cataract and glaucoma ?

A

> cataract and glaucoma often co- exist
note general reduction in sensitivity on the total deviation map
the pattern deviation reveals the focal loss

clinical skills (13 decks)

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