Brainscape's Knowledge GenomeTM

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


See full index

V2 > 3.1.4: Identifies abnormal colour vision & appreciates significance > Flashcards

3.1.4: Identifies abnormal colour vision & appreciates significance Flashcards

1
Q

What % of males have CVD? What is the breakdown of the %?

A

8% of males have CVD
5% are deuteranomolous trichromat
1% are deuteranope
1% are protanomalous trichromat
1% protanope

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

Why is it important to test colour vision?

A

Careers: pilots, armed forces, police, electrical engineers
Safety: traffic lights, electrical wiring
Pathologies

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

What is colour theory?

A
  • responses from 3 types of photoreceptor are transformed by complex neural network in retina so at level of ganglion cells colour info is coded into:
    • 2 opponent colour channels: red v green, blue v yellow
    • 1 opponent luminance channel: black v white (brightness/luminance)
  • Human eye can see 380nm - 780nm using (tricolour) three photoreceptors (S, M, L cone) of overlapping spectral sensitivity (Receptor level).
  • Cones S, M, L function at high level illuminance, rods fnction at low level illumminance
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe vision being trichromatic?

A

Each photopigment is maximally (but not exclusively) sensitive to a different region of visible EM spectrum
- Red (long wavelength 620nm - 720nm)
- Green (medium wavelength 500nm - 575nm)
- Blue (short wavelength 450nm - 490nm)
* Blue cones are absent in central fovea
* Red/green cone ratio vary greatly from person to person

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

Describe congenital CVD?

A
  • Higher incidence in men than women as X-linked autosomal recessive trait (1 in 12 males, 1 in 250 females)
    • Protan: confuse reds and greens, both appear desaturated yellow
    • Deutan: confuse reds and greens, both appear desaturated yellow
    • Tritan: confuse blues, yellows & greens, appear pink/turquoise
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe monochromats?

A
  • One functioning cone
  • Cone monochromat: single functioning cone
  • Rod monochromat: no functioning cones, leads to:
    o decreased VA
    o photophobia
    o nystagmus
    o Only percieve brightness variations
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe dichromacy (absent cone)?

A
  • 2 active cones, 1 non-active
  • Protanope 1% (L cone missing, red)
  • Deuteranope 1% (M cone missing, green)
  • Tritanope 0.001% (S cone missing, blue)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Describe anomalous trichromacy (defective cone)?

A
  • All 3 cones are active but 1 or more has abnormal sensitivity
  • Protanomaly 1% (abnormal red cone sensitivity, red defect)
  • Protanomalous: red cone sensitivity is shifted towards green cone (shorter wavelengths)
  • Deuteranomaly 4.9% (abnormal green cone sensitivity, green defect)
  • Deuteranomalous: green cone sensitivity shifted towards red cones (longer wavelengths)
  • Tritanomaly (abnormal blue cone sensitivity, blue defect)
  • Tritanomalous: blue cone sensitivity shifted towards green cone (longer wavelengths)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the colour confusion that protans, deutans or tritans may mix up?

A

Protan:
- yellow-red/yellow/green-yellow
- violet/blue-green
-purple/grey/green
- brown/green
- red/black
Deutan:
- yellow-red/yellow/green-yellow
- violet/blue-green
- purple/grey/green
- brown/green
- green/black
Tritan:
- blue-green/green
- purple/red
- yellow/white
- violet/grey/yellow-green
- dark blue/black

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Describe acquired CVD and the 3 types?

A
  • Secondary to pathology (ocular and systemic), drug linked, defects fluctuate in severity, associated with decreased VA & VF
  • Usually monocular & asymmetrical
  • Usually blue-yellow
  • Type 1: similar to protan - red/green - found in macular dystrophy/hydroxychloroquine retinal toxicity (rheumatoid arthritis)
  • Type 2: similar to deutan - red/green - found in retrobulbar optic neuritis (common with ONH defect)
  • Type 3: similar to tritan - blue found in many central & peripheral retinal lesions & lesions of visual pathway - POAG, AMD, DR
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

When should you test colour vision?

A
  • children at 1st eye test - especially boys
  • family history of CVD especially mother
  • sxs suggestive of impaired colour discrimination
  • occupational purposes
  • aid in diagnosis or investigation of ocular or systemic disease
  • suspected as side effect of medication or injury
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What should you consider when using a colour vision test?

A

Illumination
* results are only valid if the test is administered under the recommended
illumination conditions
o appearance of spectral colours changes with spectral content of the
illuminant (daylight).
Refractive correction
* perform at end of test with appropriate refraction in place
Viewing distance
* Needs to be exact to ensure observations are being made with the central rod
free retinal area
Viewing time
* Short (few seconds) to limit the effects of colour adaptation
Monocularly
* To prevent influence from the fellow (potentially unaffected) eye

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

Describe the Ishihara colour vison test?

A
  • 38 or 24 plate version (14 screening plates, 2 classification plates, pathway plates non-verbal or numeric)
  • Does not grade severity - no. of plates missed does not grade severity
  • Pass or fail
  • Classification indicate type of defect
  • 3 fails pass on 38, 2 fails pass on 24, 6 fails or more then FAIL
  • Viewing time is 4 seconds per plate
  • Viewing distance 75cm
  • Illumination needs to be at least 250 lux - daylight best - Tungston not allowed due to bias, fluorescent is allowed
  • Ishihara can ONLY detect protan & deutan –> a tritan will pass it
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe the plate types in Ishihara test?

A
  • First plate is a test plate always - only a brightenss difference
  • Transformation plates - normal sees one number, CVD sees another
  • Vanishing plates - camouflage principle, normal sees number, CVD does not
  • Hidden digit plates - only seen by CVD px
  • Classification plates - only used if screening plates failed to identify defect
  • Non-numeric - should be traced <10secs but do not touch the page

24 plate:
Plate 1 demo, P2-9: screening type transformation, P10-13: vanishing, P14-15: hidden dig, P16-17: classification plates, P18-23: tracing (if px can’t read no.s), P24 (trace everyone can do)

38 plate:
P1: demo, P2-9: transformation, P10-17: vanishing, P18-21: hidden digits, P22-25: classification, P26-38: tracing (if px can’t read no.s)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the +ves and -ves of Ishihara test?

A

+ves:
- quick and efficient
- simple to use
- high sensitivity and specificity when performed correctly
-ves:
- no tritan detecting ability
- does not diagnoses severity
- screening plates are very sensitive - risk of false +ves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe City Universitiy colour vision test (1st and 2nd edition)?

A
  • Passed by colour normals & mild CVDs
  • 10 plates - 5 colour targets per plate subtending 1.5 degrees at 35cm
  • Can be used to detect protan, deutan and tritan defect
  • Grades severity
  • Pages should be shown for 3 secs at 35cm
  • Control page first: everyone answers correctly

Section 1: page 1-6, ‘Chroma 4’: 4 dots surrounding 1 in middle, 8mm. “Which is most similar?”
Mild CV defects will not struggle much with this

Section 2: page 7-10, ‘Chroma 2’: 4 4mm coloured spots surrounding central spot. “Choose spot which most closely matches central spot.”
More difficult to distinguish closest colour, so even mild CVD will struggle.

17
Q

Describe City colour vision test 3rd edition?

A
  • no valuated data - don’t know how good it is
  • only 4 plates equivalent to 2nd edition
  • criterion (>4 errors) not validated
  • 3 coloured spots comparing to left to right row, 10 pages
17
Q

Describe Farnsworth D-15 test for colour vision?

A
  • Arrangement test - sort coloured samples in order of hue/shade appearance
  • 15 Munsell coloured caps & 1 reference cap (starting point)
  • Arrange 15 coloured caps into natural colour sequence
  • 50cm viewing distance, allow 1-2mins
  • Optom plots order on recording sheet using no.s on base of caps (“join the dots” style recording sheet - shape shows defect present)
  • Not a screening test
  • Detects ~5% of CVD in males, 3% of males w/ CVD will pass it
18
Q

What does Farnsworth D15 test classify and what are major and minor errors?

A

Classify: type of CVD and severity
Determines type of defect: protan, deutan or tritan - compare cross over lines with colour confusion axes
Failure: single error of 2 steps or more

Major errors: crossing errors where px cross circle - severe CVD will make these - if px mkes 1 or more then mod-severe CVD

Minor errors: px gets adjacent caps mixed up - can occur in colour normals (some pxs not good at arranging colours) - colour normal or mild CVD will make 1 or 2 minor erros

19
Q

What is desaturated D15 test used for?

A

to classify mild CVD, acquired CVD or to detect & monitor pathology

20
Q

What are the +ves and -ves of D15 colour vision test?

A

+ves:
- grades severity
- simple & quick
- can classify protan, deutan & tritan defects
-ves:
- not suitable for young children
- does not formally identify anomalous trichromats vs dichromats

21
Q

What are the occupational vision standards in terms of colour vision?

A
  • Army: person able to still distinguish between red/green may still be allowed for certain roles
  • Air service/Pilots: ishihara 38 plates - 9 or more wrong on (1-21), 24 plates - 7 or more wrong on (1-15)
  • Fire service: no monochromats or dichromats. Anomalous trichromats need testing (protanomalous likely fail, deutranomalous may pass)
  • Police: no monochromats. Mild/severe anomalous trichromats & dichromats allowed but need coping strategies.
  • Electrical engineers: need to pass a Clinical Aviation Marine (CAM) lantern test - no official standard but likely no CVD allowed
22
Q

Name other CVD tests that are available?

A

Farnsworth Munsell (FM) 100 hue test - takes ages, larger version of D15
HRR - similar to Ishihara in principle but can classify tritan
Nagel Anomaloscope - produces a quantitative measure of the type and degree of a colour deficiency. The gold standard and most commonly used is the Nagel anomaloscope which assesses red/green deficiency

V2 (28 decks)

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