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PART ONE REVISION. > CLINICAL TECHNIQUES - Visual Fields and Electrodiagnostics > Flashcards

CLINICAL TECHNIQUES - Visual Fields and Electrodiagnostics Flashcards

1
Q

F

What is the normal extension of visual field? Superior, Nasal, Inferior, Temporal.

A

Superior: 60 degrees
Nasal: 60 degrees
Inferior: 75 degrees
Temporal: 100 degrees.

Total Horizontal: 160 degrees
Total Vertical

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2
Q

What is kinetic perimetry?

A

A kinetic target is moved from non-seeing area to seeing area - measures extent of visual field.

2D measurement of hill of vision.

All locations where stimulutus is first seen has equal sensitivity, so these points form a ringed shaped locus of points called an isoptic.

It can accurately plot outline of the border of the defect but cannot assess depth.

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3
Q

What are examples of kinetic perimetry? (4)

A
  1. Confrontration perimetry
  2. Tangent perimetry
  3. ARC Perimetry
  4. Goldmann Perimetry
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4
Q

What is Goldmann’s perimeter?
What type of perimetry can it do?
What is its range of illuination?

A

Hemispheric dome presents target at 33cm away from cornea.
Both static and kinetic perimetry.

Background illumination of 31.5 apostlibs, maximum brightness of 1000 apostlibs.

Isopters are used to show VF areas of equal or greater sensitivity, each isopter represents a different stimulus size to patient.

Size and intensity of targets are varied to plot different isopters

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5
Q

What is static perimetry?

A

Measures retinal sensitivity at individual points of the retina.

It is a 3D assessment of predetermined points in hill of vision

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6
Q

What are the different types of static perimetry?

A

Octopus
Humphrey

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7
Q
A
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8
Q

What is automated perimetry?

A

Constant size stimulus against constant background illumination is presented at varied light intensities at particular points, minimum intensity necessary for detection of stimulus is recorded as the threshold.

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9
Q

What is light intensity measured in? What is the maximum in humphreys?
What is retinal intensity measured in?

What is the relationship between light intensity and retinal sensitivity?

A

Light intensity: Apostlibs / decibels. Maximum is 10,000 apostlibs. Standard is 31.5

Retinal sensitivity: Decibel units.

Decibels is the inverse of apostlibs

Decibels is directly proportional to retinal sensitivity

Apostlibs is inversly proportional to retinal sensitivity

Low Db value –> high intensity of light stimulus is needed –> low retinal sensitivity.

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10
Q

What is the difference between suprathreshold stimulus and infrathreshold stimulus?

A

Suprathreshold: Brighter than threshold and seen more than 50% of the time –> used in screening tests.

Infrathreshold: Dimmer than threshold and seen less than 50% of the time.

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11
Q

How many points are tested in 24 degree strategy in Humphreys?

A

54 points.

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12
Q

What is the optimum pupil size?

A

3-4mm
Less than 2mm causes diffuse field depression or edge scotomas

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13
Q

What is the fixation loss % rate that is reliable?

A

Less than 20%.

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14
Q

Why do we check for pattern deviation plots?

A

They bring out deep scotomas.

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15
Q

What is short term fluctuations? What is normal?

A

Index of intratest variation - retests 10 predetermined points and checks for consistency.

Normal < 3 dB

More than this indicates unreliability / possibly pathology.

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16
Q

What is global indices?

A

Summary of results condensed into one figure.

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17
Q

What is total deviation?
What is mean deviation?

A

Total: Deviation of patients result from age-matched controls

Mean: Average deviation of sensitivity from adge adjusted normal population

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18
Q

What is pattern standard deviation?
What is correct pattern standard deviation?

A

PSD: Adjusted for generalised depression - eg highlights focal depression in a field which might be masked by general deviation such as cataracts

Corrected PSD: After accounting for short-term fluctuation.

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19
Q

What does ERG measure?

A

Measures electrical response of various cell types in the retina (photoreceptors, bipolar cells, ganglion cells) which results in a biphasic waveform.

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20
Q

What are the types of ERG?

A

Based on zone of the stimulus
1. Full Field
2. Focal ERG
3. Multi-focal ERG

Based on types of stimulus
1. Single flash
2. Flicker fash
3. Red flash
4. Blue filter flash
5. Pattern ERG

Based on state of adaptation
1. Scotopic ERG (dark)
2. Photopic ERG (light)
3. Mesopic ERG (mixed)

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21
Q

What is the mechanism of ERG?

A
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22
Q

What are the different waveforms of the ERG?

A

Biphasic waveform

**A wave: negative wave from photoreceptors (rods and cones - hyperpolarisation). A1 - cones, A2 - rods

Oscillatory potentials: amacrine cells: ascending limb of B wave, high frequency low amplitude wavelets

B wave: bipolar cells and muller cells (depolarisation wave)**

C waves: RPE - occurs

D waves: bipolar cells

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23
Q

What is the difference between amplitude and latency and implicit time of the waveforms?

A

a wave amplitude: baseline to trough
b wave amplitude: a trough to b crest.

a wave latency: time taken to start a wave
b wave latency: time taken to start b wave

a wave implicit time: time taken from flash onset to peak of each wave.

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24
Q

What does the oscillatory potential measure?

A

Oscillatory potential: Measures amacrine cells –> gives perfusion status on INNER retina –> it is reduced in retinal ischaemic states.

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25
Q

What patient factors affect light stimulus entering the eye? (2)

A
  1. Pupil sze
  2. Opaque media
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26
Q

WHat is the critical fusion frequency? What is the difference between rods and cons?

A

Maximum frequency that can be perceived as flickering

Rods: 20Hz
Cones: 60Hz

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27
Q

What is the interpretation of reduced b wave with preserved a wave?

A

normal photoreceptors but abnormal bipolar cells –> CRAO, congenital stational night blindness and retinoschisis.

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28
Q

What is the interpretation of Reduced photopic response but normal scotopic response?

A

Cone dystrophies, achromatopsia

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29
Q

What is the interpretation of no response on ERG?

A

Batten’s disease
Leber’s congenital amaurosis

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30
Q

What is the interpretation of increased a wave?

A

Albinism

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31
Q

Does the ERG pick up small localised lesions in the macula?

A

No - use pattern ERG to pick this up.

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32
Q

What are the 3 responses seen in a pattern ERG?

A

N-35 wave - negative
P-50 wave - positive (macular photoreceptors)
N-95 wave - negative (ganglion cell layer)

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33
Q

Where must the electrode be placed on pattern ERG?

A

Ipsilateral temple / outer canthus to avoid interference from cortical evoked potential.

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34
Q

What does the electro-oculogram measure?

How is it measured?

A

Resting potential between cornea and back of retina.

Measure resting potential at dark phase and measure potential at light phase.

Arden index =
maximum height of light peak / minimum height of dark peak.

If > 1.85 - normal
If < 1.65 - highly abnormal

35
Q

When is electro-oculogram most useful?

A

More specific in disease between RPE and photoreceptors –

  1. Best vitelliform dystrophy
  2. Chloroquine toxicity
36
Q

What is visual evoked potentials? What types of VEP are there and where do they arise from?

A

Measurement of occipital / cortical electrial response to flash or pattern stimulus –> measures optic nerve function and quantifies function between retina and cortex.

pattern VEP: V1 area of cortex
flash VEP: V2 area of cortex

37
Q

What is the waveform seen in VEPs?

Which is the most useful measurement?

A

Triphasic morphology

N75
P100 - macular response
N135

P100 latency (most useful)
Amplitude is also useful - approximates to VA.

38
Q

What are the VEP findings in albinism?

What are the VEP findings in ambylopia?

A

Albinism - enhanced cross-over (larger proportion of retinal ganglion cells fibres cross at the chiasm)

Ambylopia: Flash VEP normal, pattern VEP abnormal.

39
Q

How many points are tested in the

  1. 24-2 test
  2. 10-2 test
  3. 30-2 test
A

24-2: 54 points
10-2: 68 points
30-2: 76 points

40
Q

What is the SITA algorithm?

A

Swedish Interactive Threshold Algorithm - shortens the time needed to complete the test –> takes 7 minutes per eye.

41
Q

What is cloverleaf defect pattern?

A

Visual field does not correlate to any anatomical defect - sign of poor visual attention/malingering.

42
Q

What are the reliability scores for
1. Fixation Loss
2. False Positive
3. False Negative

A
  1. Fixation Loss - 5% of stimuli go to blind spot - >20 % is unreliable
  2. False positive: >20% unreliable, >33%
  3. False negative: >20% unreliable
43
Q

Which part of VF test is used to measure the depth of the defect?

A

The mean deviation.

44
Q

What are the causes of edge scotomas of visual field? (3)

A
  1. pupil size < 2mm
  2. High false negative rate
  3. Lens rim artefact
45
Q

What are the caues of increased AUTOFLOURESENCE

What are the causes of decreased AUTO-FLOURESENCE

Which disease has both increased and decreased autoflouresence?

A

Increased:
1. RPE dysfunction (increased metabolism)
2. Loss of photopigment
3. Subretinal autoflourescent material

Decreased
1. RPE atrophy
2. Blockage of RPE cells

In posterior uveitis, active disease has increased autoflouresence

Inactivate disease has reduced autoflouresence

46
Q

What area of the central retina does multi-focal ERG cover (in degrees)?

A

30 degrees with 250 focal points.

47
Q

Each small square of a Hess Chart subtends to a degree of?

When is a Hess Chart used for?

A

5 degrees at 50cm working distance

Hess Chart: used for measuring eye movement for blow-out orbital fractures

48
Q

What are Hess Charts used for?

A

Incomitant strabismus - angle of deviation of squinting eye not the same in all directions.

Incomitant strabismus –> inconsistent strabismus.

49
Q

What is a Hess Chart?

A

Tangent screen used to map the relative position of eye in 9 positions of gaze - chart includes horizontal and vertical lines that subtend a visual angle of 5 degrees

Has inner field and outer field

50
Q

What does the inner field of the Hess Chart test for?

What does the outer field of the Hess Chart test for?

A

Inner: 9 testing points of 3 small sqaures - inner field measures 15 degrees.

Outer: 16 testing points of 9 small squares - outer field measures 30 degrees

51
Q

What colour Hess Chart goggles are used and what is each used for?

A

Eyes are dissociated with green/red goggles
Red goggle - fixing eye
Green goggle - test eye

52
Q

What are the main principles used in Hess Chart (3)

A
  1. Foveal projection and Haploscopic principle
  2. Herrings and Sherington’s Law
  3. Dissociation of eyes.
53
Q

What is the haploscopic principle?

A

Division of physical space into two separate areas of visual spaces which are visible to one eye only.

54
Q

What are the contraindications to Hess Charting? (3)

A
  1. Abnormal retinal correspondence
  2. Suppression
  3. Colour blindness
55
Q

In automated visual field testing, which stimulus size is most commonly used?

A

Goldmann III - approximately 0.5 degrees in diameter

56
Q

What is the size of the normal blind spot?

A

10 degrees in diameter, 10-20 degrees from central fixation point

57
Q

Which conditions produce a normal a wave and reduced b wave (negative ERG with b wave amplitude lower than a wave) (4)

A
  1. CRAO
  2. CRVO
  3. Congenital stationary night blindness
  4. X linked juvenile retinoschisis
58
Q

What colour testing does Ishihara test?

A

Red-Green colour deficiency

59
Q

What plate can assess blue axis?

A

Hardy-Rand-Rittler

60
Q

What are the VEP findings in optic neuritis?

A

Decreased amplitude and increased latency of P100

61
Q

Flash vs pattern reversal VEP- which patients to use them for?

A

Flash: unco-operative patients (infants, comatose), .

Pattern reversal: Pupil dilation contraindicateed, correction of refractive error is necesary.

62
Q

When is pattern ERG used for?

A

Can differentiate macular vs optic nerve dysfunction

Macular: reduced P50 amplitude, response delay.

Optic nerve dysfunction (optic neuritis, MS): normal P50, decreased N95 amplitude with primary retinal ganglion cell dysfunction

63
Q

What does electro-oculogram evaluate?

What does multi-focal and pattern ERG evaluate?

A

electro-oculogram - outer retina and RPE.

multi-focal ERG - individual areas of macula
pattern ERG - ganglion cell function

64
Q

What is the difference between neurogenic palsy and mechanical palsy in interpretation of a Hess Chart in these parameters:

  1. Field shape and size
  2. Spacing between inner and outer fields
  3. Muscle sequelae
A

See table.

65
Q

What is the difference between frequency doubling perimetry and short wavelength automated perimetry?

A

FDT: preferientally assesses ganglion cells of Magnocellular (M-cells) pathway using rapidly reversing broad and white bars, creating double frequency illusion. M Fibres are lost in early glaucoma.

SWAP: Uses blue test object on a yellow background, targets koniocellular pathway (small bistratified ganglion cells projecting to koniocellular layers of LGN)

66
Q

What do these represent in Goldmann perimetry interpretation?

  1. Roman Numerals
  2. Standard Numbers
  3. a-e?
A
  1. Roman numerals - size of target - each number equivalent to 4-times increase
  2. Arabic numbers - intensity of light, each stage is 3 x brighter measured in asb or increase in 0.5 log units.
  3. a-e: additional minor filters where a is darkest and e is brightest. Each letter is increase of 0.1 log unit.
67
Q

What do sloping fields indicate the presence of in a Hess Chart?

A

Presence of A/V patterns.

68
Q

What condition would affect EOG but leave ERG unaffected?

A

Best vitelliform dystrophy - only affects EOG.

69
Q

What is the optimal frequency for perception of flicker?

A

10Hz.

70
Q

What is the maximal ERG and when is it used?

A

Dark-adapted (scotopic) eyes using bright white flash - mixed rod and cone response.

71
Q

Which type of reliability indices is most deterimental in automated visual perimetry?

A

False positive - minimise or mask an actual scotoma.

72
Q

Which parameter does the visual field index take into account the most?

A

Pattern deviation probability map and total deviation map. Gives more weight to central points.

73
Q

There is delay in 30Hz flicker test. Where is the pathology?

There is reduced amplitude in 30Hz flicker test. There is no delay. Where is the pathology?

A

Delay: General cone problem
Reduced amplitude: Focal cone problem

74
Q

How can you check refractive correction has been done properly on humphrey VF?

A

VA and foveal hypersensitivity should match - 6/6 = 35dB.

75
Q

What is the normal progression rate of mean deviation per year in humphreys?

A

0.08

76
Q

In 10-2 visual field how many degrees are central points away from FIXATION?

A

1 degree

77
Q

How long is a stimulus typically shone for in a HVF?

A

200 milliseconds (0.2 seconds)

78
Q

What are the causes of a cecocentral scotoma (pathology from disc to macula)?

A

Inherited optic disc pathology (Leber’s autosomal dominant optic atrophy),

Optic disc pit with serous detachment.

79
Q

What are the causes of arcuate scotoma? (damage to nerve fibre bundles that extend to blind spot)

What are the causes of altiduinal defect

A

Arcuate:
1. Glaucoma
2. optic nerve drusen
3. AION
4. Branch retinal vein/artery occlusion

Altiduinal defect - damage to optic disc poles
1. Hemiretinal artery/vein occlusion
2. Optic neuritis
3. AION

80
Q

How many poitns of the central retina does the multi-focal ERG detect?

A

250 points.

81
Q

What strategy is used to detect the threshold stimulus intensity?

A

Bracketing

82
Q

AMSLER grid tests how much visual field centred on fixation?

A

20 degrees of visual field.

83
Q

What score is used for early localisation defect detection in glaucoma in HVF?

A

Pattern STANDARD deviation.

84
Q

What area of central retina does the multi-focal ERG cover (in degrees)? How many points?

A

30 degrees with 250 focal points.

PART ONE REVISION. (77 decks)

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