Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Assessment of Vision 1 > Week 3: Perimetry > Flashcards

Week 3: Perimetry Flashcards

1
Q

Define visual field and perimetry

A
  • Visual field = the area of space perceived by the eyes sensitivity to light
  • Perimetry = plotting the sensitivity of this area in space
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the boundaries of monocular visual field?

A
  • superiorly = 50-60 degrees
  • nasally = 60 degrees
  • inferiorly = 70-75 degrees
  • temporally = 90-100 degrees
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How are visual fields assessed?

A
  1. Mapping the boundaries of the field
  2. Measure the sensitivity of the eye in detecting a stimulus in different regions of visual field

The use of Weber’s Law = ΔL/L = C
- Where; difference in threshold (ΔL) & visible relative to background (L) is constant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the Weber’s Law dependent on?

A
  1. Background photopic luminance (10 cd/m2)
  2. Pupil size > 2mm
  3. Clear Ocular media
  4. Test conditions – stimulus size, duration etc
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Explain the ‘normal visual field’

A
  • Images are inverted & flipped as they pass through the lens with a significant amount of overlap
  • Images projected onto retina can be divided left and right with FOVEA at the centre
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does right Nasal retina view?

A

Views right half of visual field

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What does the Right Temporal retina view?

A

Views left half of visual field

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does Homonymous view?

A

Right nasal retina & left temporal retina project the same area in visual space to visual cortex

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the dimension of degrees for binocular visual field (horizontal & central field)?

A
  • Horizontal visual field = +/- 90 degrees (central 180 degrees visual space)
  • Binocular central visual field = +/- 30 degrees (central 60 degrees visual space)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What does ‘traquair’ mean?

A

“an island of vision in a sea of darkness”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Define Hill of Vision

A

Visual function is not uniform across the whole visual field

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

In the hill of vision what is in the central and peripheral retina?

A

Central Retina:
1. High density cones – good colour vision
2. Low density rods - responsible for good central vision
3. Good visual acuity
4. Peak of ‘hill of vision’

Peripheral Retina:
1. Low density of cones
2. High density of rods
3. Poor visual acuity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the blind spot in HOV?

A

-15° temporal to fixation
- 2° below horizontal meridian

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Define isopters

A
  • Areas of equal sensitivity
  • Connection points are joined together
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the testing conditions in HOV?

A
  1. Photopic – Brightly lit condition
  2. Mesopic – Dim condition (twilight)
  3. Scotopic – Dark condition
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why perform perimetry?

A
  1. Diagnosis of Visual pathway pathology such as; glaucoma management, neurological disorders, retinal diseases
  2. Monitor change in function
    - Assess baseline severity of vision
    - Measure lesion progression over time
17
Q

List the traditional/objective perimetry

A
  1. Kinetic
  2. Static
  3. Suprathreshold Static
18
Q

Briefly explain kinetic perimetry

A
  • Detection of moving target
  • Stimulus repeated along different meridians
  • Different spot intensities used
19
Q

List advantages/disadvantages of kinetic perimetry

A

Advantages:
- Ability to characterise entire central and peripheral visual field
- Flexibility and interaction between examiner and patient
- Accurately characterise the shape of visual field scotomas

Disadvantages:
- Higher variability than other forms of perimetry
- Difference in clinical performance between examiners

20
Q

Briefly explain static perimetry

A
  • Stationary target with varying brightness
  • Brightness is increased until threshold
  • Most common method of measuring HOV
21
Q

List advantages/disadvantages of static perimetry

A

Advantages:
- Standardised test procedure
- Ability to exchange information between devices/clinics
- Age corrected normative databases
- Monitoring response reliability

Disadvantages:
- Time consuming and greater burden on patient attention and performance
- High test-retest variability
- Less flexible

22
Q

Briefly explain suprathreshold static perimetry

A
  • Rapid screening procedure to detect gross defects
  • Typically a smaller number of targets used
23
Q

List the new perimetry techniques

A
  1. Short Wavelength Automated Perimetry (SWAP)
  2. Frequency Doubling Technology (FDT)
  3. Flicker Perimetry
  4. Motion Perimetry
  5. High Pass Resolution Perimetry
24
Q

Briefly explain short wavelength automated perimetry (SWAP)

A
  • To permit use of short-wavelength-sensitive light (blue) stimuli on a yellow background in a similar duration
25
Q

List advantages/disadvantages of short wavelength automated perimetry (SWAP)

A

Advantage:
- Principle of Redundancy

Disadvantages:
- Greater variability and reproducibility between tests
- Adversely affected by cataracts

26
Q

Briefly explain frequency doubling technology (FDT)

A
  • Tests an illusion
  • The illusion is that there are twice as many dark and light bars present
  • Task is to determine the minimum contrast where the stimulus can be detected
27
Q

List advantages/disadvantages of frequency doubling technology (FDT)

A

Advantages:
- Principle of Redundancy
- Results are unaffected by refractive errors up to 6D
- Very rapid screening test 90 sec with at sensitivity of 94% (true positives)

Disadvantage:
- Poor spatial assessment of visual field loss

28
Q

Briefly explain flicker perimetry

A
  • Determining highest temporal frequency
  • Can be an early indicator of functional loss in glaucoma
29
Q

List disadvantages of Flicker Perimetry

A
  • Loss of flicker sensitivity
  • Is affected by pupil size and other pathological conditions
30
Q

Briefly explain motion perimetry

A
  • Detection of rapid movement of a single stimulus presented at various visual field locations
  • Tested using computer based programs
  • Were found to be more sensitive for nerve fibre bundle-shaped defect compared to conventional perimetry
31
Q

List disadvantages of Motion Perimetry

A
  • Motion can be detected by both Parvocellular and Magnocellular cells, therefore this selectivity does notmean exclusivity
  • Optical defocus does affect foveal motion thresholds
32
Q

What are Factors Affecting Visual Field Sensitivity Profile

A

Stimulus (sport of light) factors:
1. Size
2. Duration
3. Colour
4. Background Luminance

Patient Factors:
1. Dark adaptation level
2. Age
3. Blurred / low vision (uncorrected refractive error)

33
Q

Describe Ricco’s Law

A
  • Describe a human’s ability to visually detect targets on a uniform background

Luminance Threshold x Area = Constant

  • Larger the spot size, lower the threshold
34
Q

Describe Bloch’s Law

A
  • For relatively short presentations, the product of contrast and duration is constant at the detection threshold

Luminance Threshold x Duration = Constant

35
Q

Briefly describe background luminance

A
  • Background luminance = 10 cd/m2
  • Contrast needed to just detect stimulus from uniform background
  • 0 dB sensitivity = no response to brightest stimulus produced by instrument
36
Q

What are the advantages of background luminance?

A
  • Shorter adaptation time
  • Reduced sensitivity to changes in room luminance during testing
37
Q

What is the effect of blurred vision on visual sensitivity?

A
  • Retinal defocus increases detection threshold and produces flatter HOV
  • Contrast needed to just detect stimulus from uniform background

Assessment of Vision 1 (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions