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Assessment of Vision 1 > Week 4: Visual Field > Flashcards

Week 4: Visual Field Flashcards

1
Q

What are the three kinetic perimetry?

A
  1. Confrontation
  2. Tangent Screen
  3. Goldmann
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2
Q

Briefly explain confrontation test

A
  • Simplest way to test the visual field
  • Examiner sits opposite the patient at the same eye level at a distance of 1 m
  • Px & examiner cover the opposite eye, therefore uncovered eyes have mutually congruent fields
  • Examiner then introduces a test target into the field from the periphery until target is perceived by the px
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3
Q

What are the advantages and disadvantages of confrontation tests?

A

Advantages:
- Quick
- Cheap
- Effective with young children
- Detects gross field defects
- Hemianopia will be obvious

Disadvantages:
- Virtually useless in clinic
- No control of luminance, contrast
- Recognition of defect depends on skill of examiner

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4
Q

List the method for peripheral visual field

A
  1. Px is asked to continue looking at examiner’s nose and to say “yes” when they are aware of a target moving in their peripheral vision
  2. Slowly move the target in from the periphery from the following ‘clock’ positions: first 12, 3, 6 & 9 o’clock in random order
  3. If a visual field defect is found, additional positions are assessed
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5
Q

List the method for central visual field

A
  1. Px is asked to continue looking at examiner’s nose and is asked whether they can see all parts of the examiners face, or whether part or one side of the face appears blurred or faded than the rest
  2. Px should consider whether right versus left eyes, mouth versus forehead, right versus left ears are seen equally well to further qualify their responses
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6
Q

List the method for finger counting confrontation

A
  1. Hold both hands up (with fingers closed), one hand positioned to the outer side of the each of the pxs’ eyes
  2. Briefly raise 1 or 2 fingers from one hand & ask px to say whether fingers were raised and if so, how many were seen?
  3. Repeat this with both hands held in the lower quadrants (below the patient’s cheek level)
  4. Finally, briefly raise fingers on both hands and ask patient how many are seen in total
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7
Q

List the method for tangent screen

A
  1. Px is 1 m from black velvet screen
  2. Target is a small disc moved from periphery to centre until seen by px
  3. Examiner marks the area where target seen with black pin and plots the isopter of the target
  4. Target size depends on vision of patient (6/6 patient = 2 mm target & 6/60 = 10 mm target)
  5. Can be adapted to patients with central field loss and have poor fixation control
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8
Q

What are the advantages and disadvantages of tangent screen?

A

Advantages:
- Versatile and flexible
- Good for detection of contraction of visual field

Disadvantages:
- Requires skilled operator
- Results are operator dependent
- Time consuming
- Poor sensitivity for detecting scotomas

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9
Q

Briefly explain the Goldmann test

A
  • Hemispherical bowl that is uniformly illuminated background 10 cd/m2 and target light of varying size & brightness are projected
  • Px sits in front of machine with their eye fixed on the centre of the hemisphere
  • The target is introduced and the patient signal perception of the target using a buzzer
  • The examiner marks the chart and plots the isopter pertaining to each target
  • Several isopters are plotted of varying target size and brightness
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10
Q

What are the advantages and disadvantages of Goldmann tests?

A

Advantages:
- Assess full field
- Useful for assessing neurological field defects
- Good control over stimulus & background
- System for monitoring fixation
- Semi-automated recording

Disadvantages:
- Examiner dependent
- Requires a skilled examiner
- Time consuming
- Poor sensitivity for detecting scotomas

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11
Q

What are the three static perimetry?

A
  1. Amsler grid
  2. Humphery
  3. Bejerrum screen
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12
Q

Briefly describe amsler grid

A
  • Assess central 10° of visual field qualitatively, each square 1° on retina
  • Rapid & effective method for detecting macular abnormalities or unexplained decrease in vision
  • Test is monocularly
  • Px holds the grid 30 cm distance and fixates on central dot & must wear near Rx
  • They identify regions that are blurry, distorted
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13
Q

What are the advantages and disadvantages of amsler grid?

A

Advantages:
- Quick
- Cheap
- Abnormalities can be drawn
- Grids can monitor change

Disadvantages:
- Poor spatial resolution
- Difficult for low vision px
- Difficult for px with large central loss

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14
Q

Briefly describe the Humphrey Field Analyser

A
  • Stimuli size are randomly shown at fixed locations with background constant photopic luminance of 21.5 asb
  • Brightness is increased until threshold detected by patient
  • Assesses monocular visual function outside the fovea
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15
Q

What are the four full threshold & screening methods for the Humphrey Field Analyser?

A
  • 30-2 or 24-2 SITA Standard
    Test algorithm (4-8 mins/eye)
  • 30-2 or 24-2 SITA Fast
    Diagnostic sensitivity to full threshold (2-6 mins/eye)
  • 30-2 – 76 test point locations
    Covers central 30°
  • 24-2 – 54 test points
    Covers central 24° - except nasally extends to 30°
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16
Q

What is the first step when starting the humphrey field analyser?

A
  1. Enter patients information
    - Px’s name
    - ID number
    - Birth date – for normative database comparison
    - VA and pupil size (optional)
    - Eye tested will appear on print out – RE always 1st
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17
Q

What is the fixation monitoring for HFA?

A
  • Encouraged by display of fixation target & short stimulus duration
  • Heijl-Krakau blind spot monitoring: stimuli are periodically presented at the blind spot during the test. If seen counted as ‘fixation loss’
  • Score is given regarding number of fixation losses
  • Upward deflection = amount of gaze error at each stimulus
  • Downward deflection = unsuccessful measurement (due to blink
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18
Q

What are the sensitivity values derived for HFA?

A
  • If patient cannot see a light of max intensity, they are defined by HFA as having sensitivity of 0 dB
  • Numbers in main field plot = sensitivity values (dB)
  • Threshold = intensity of stimulus seen 50% of the time
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19
Q

What are the reliability indices (catch trials) for HFA?

A
  • Fixation loss = number of times the stimulus was seen when it was presented at the blind spot (2/25)
  • False Positives (FP) = ‘trigger happy’ seeing a non-existent stimuli
  • False negatives (FN) = A bright above threshold flash presented & px fails to detect it
20
Q

Define Gray Scale Map

A

Pictorial representation of visual sensitivity with darker shades = lower sensitivity shading is interpolated between points & may not be representative of real defects

21
Q

What is the total deviation map?

A
  • All perimeters have age-matched normative database to which each point is compared
  • The value represents the difference
  • To determine if this is significant the variance of normal group must be taken into account
  • This is what the probability plot produces using a t-test
    -The greater the deviation the darker the symbol
22
Q

What is the pattern deviation maps?

A
  • This is the most important map to determine if a defect is present or not
  • P < 1% indicates that less than 1% of the normal population have a sensitivity lower than that at that point
  • Therefore, the darker the symbol, the lower the P value, & more abnormal the measure
23
Q

Define Mean Deviation

A

The mean of all the values in the total deviation map
- Strongly affected by refractive errors & cataracts however useful for monitoring change over time

24
Q

Define Pattern Deviation

A

The mean of the values on the pattern deviation plots

25
Q

Define Short Term Fluctuation

A
  • Checked from points that were tested twice
  • A value < 2 dB indicates consistent performance
  • Higher fluctuations occur with inattentive subjects who also have high False Negatives
26
Q

Define Corrected Pattern Standard Deviation

A

Adjusts the pattern deviation downward based on Short-term Fluctuation (SF)

27
Q

What is Hill of Vision (HOV)?

A
  • ‘Hill of vision’, visual fields are three-dimensional X (width), Y (height), Z (depth)
28
Q

What is Generalised sensitivity loss?

A

Due to change in ocular media, pathology to various portions of visual pathway, attentional or cognitive factors

29
Q

What is Ring Scotomas?

A

Indicative of retinal pathology or lens defect

30
Q

What is Central Scotomas?

A

Indicative of macular disease or optic neuropathies

31
Q

What is Defects that respect horizontal midline

A

Associated with retinal nerve fibre bundles related to optic neuropathy (glaucoma) or Branch Retinal Vein Occlusion (BRVO)

32
Q

What is Arcuate scotomas ?

A

Typical of arcuate nerve fibre bundle loss

33
Q

What is Nasal step?

A

Defects associated with optic neuropathy (glaucoma)

34
Q

What is Defects that respect vertical midline?

A

Damage to visual pathway on or after optic chiasm

35
Q

What is Homonymous defects?

A

Damage to visual pathway on same side occurring after the optic chiasm (can be within optic radiations)

36
Q

What is Congruous or incongruous defects?

A

Greater the amount of incongruity of homonymous defect between eyes the closer the site of damage to optic chiasm

37
Q

What is Pie in the sky defect?

A

A homonymous defect that resembles a piece of pie in the superior field of both eyes usually associated with temporal lobe lesion

38
Q

What is Pie on the floor defect?

A

Homonymous defect inferiorly associated with parietal lobe lesion

39
Q

What is Cookie-cutter punched out lesions?

A

Indicative of an occipital lobe lesion

40
Q

Interpreting the Visual Field

A
  • The gray scale & numbers of visual sensitivity plot are useful in gauging how severe the defect is
  • Basic statistical principles:
    P value < 0.05 at a single point = normal subject would have a sensitivity at or below that value is 1 in 20 chance
  • Highly likely that a normal subject would get a few low scores just by chance
  • In conclusion: we look for patterns of loss NOT single random scattered points
41
Q

What are the steps of interpreting the visual field?

A
  1. Detection: within normal limits or are there abnormalities
  2. Identification: loss of pattern? visual field loss unilateral or bilateral?
  3. Differential diagnosis: where is the general location of defect?
  4. Staging of the visual field loss: severity? sudden or gradual?
  5. Artefactual visual field loss
  6. Functional visual field loss
  7. Longitudinal follow-up of visual field loss
    1. Practical visual field issues
42
Q

Validity & Indices for Visual Fields

A
  • Fixation losses, False positives (FP) & false negatives (FN), FP often the most critical
  • Error rate 5-10% significantly affects the appearance.
  • Reliability indices:
  • High fixation losses > 15-20 % = inaccurate test results
  • False Positives- “trigger happy”. Field may look normal or “cleaner” (with fewer defects depicted) for values of 5-10% or higher
  • False negatives 10-15% shows that patient is not paying good attention
43
Q

Explain the basic visual pathway

A
  • Visual perception is divided into right and left hemifields & each eye receives information regarding both hemifields
  • A point source seen by both eyes will be imaged on one nasal retina and one temporal retina
  • The brain functions on a crossed wires system
  • Left half of brain controls right side of the body and vice versa
  • Left half of the brain processes images from right side of visual space
44
Q

What happens when you damage the visual pathway before optic chiasm?

A

Affect one eye, both hemifields

45
Q

What happens when you damage the visual pathway after optic chiasm?

A

Affect both eyes, one hemifield

46
Q

Explain Meyer’s Loop

A
  • The lens inverts all images, the lower half of the retina sees the upper half of the world
  • This orientation is preserved through the pathway, so that the lower optic radiations, or Meyer’s loop, are carrying information from the upper visual world

Assessment of Vision 1 (10 decks)

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