Colour vision tests Flashcards
what is a protan described as
a general term stating that the long cone photo-pigment is different from normal
what is a deutan described as
a general term stating that the medium cone photo-pigment is different from normal
what is a tritan described as
a general term stating that the short cone photo-pigment is different from normal
what is the name if someone who has a missing long/L photo-pigment cone
protanope
what is the name if someone who has a missing medium/M photo-pigment cone
deutranope
what is the name if someone who has a missing short/S photo-pigment cone
tritanope
what is the name if someone who has one of their L, M or S cones missing
dichromat
what is the name if someone who has all three cones S, M and L present, but one is anomalous (different from normal)
trichromat (S, M or L spectral sensitivity is anomalous)
what is is called if someone has an anomalous L cone spectral sensitivity
protanomalous
what is is called if someone has an anomalous M cone spectral sensitivity
deutranomalous
what is is called if someone has an anomalous S cone spectral sensitivity
tritanomalous
what is a normal trichromat
there are 3 cones with L, M and S in the ‘normal group’
what is a cone monochromat
when two cones are missing
what is a rod monochromat
when all three cones are missing
list the three main colour vision tests
- ishihara
- anomoloscope
- 100 hue and D15
which type of plates does the ishihara test use
pseudoisochromatic plates
which colour vision test uses colour matching
the anomoloscope
which test uses confusion lines
100 hue and D15
what is the general layout of the ishihara test plates
- groups of spots with similar hues and lightness seen as a number or symbol
- confusions affect the shape seen
what are the 3 main advantages of the ishihara test
- quick, simple and cheap
- screens main deficiencies
- good sensitivity and useful specificity
how many plates are in a ishihara test
38 plates
how many errors will most normals make with a ishihara test
less than 5 (0-5)
hw many errors will a RGD make with a ishihara test
9 or more errors
what is the lighting recommendation when testing with the ishihara test
300 - 500 lux
excellent colour rendering e.g. - north sky daylight or - standard illuminant D65 or - macbeth lamp
which lighting conditions are not idea when testing with the ishihara test and why
tungsten, LED and fluorescent lighting
to avoid disadvantaging the subject with low levels of colour rendering
list the 4 types of patients that the ishihara test is used on
- all new patients
- children
- to see if occupational tests are required
- general use for reports of colour disturbance, pathology and medication
what is plate 1 of the ishihara test and who is it seen by
a demonstation plate - seen by all observers
what are plates 2-9 of the ishihara test and who is it seen by
transformation plate - detected by normals but not RGDs
what are plates 10-17 of the ishihara test and who is it seen by
vanishing digit - detected by normals but not RGDs
what are plates 18-21 of the ishihara test and who is it seen by
hidden digit - not detected by normals but seen by RGDs
what are the plates 22-25 of the ishihara test and who is it seen by
it is used to differentiate between protan and deutan
which type of colour deficient people does the ishihara test for and which types are not detected
detects of red-green colour deficients (RGDs)
not tritan defects (but this is not a serious drawback)
what is a disadvantage to the ishihara plate test
unable to differentiate reliably between whether its anomalous trichromats or dichromats
if a fire fighter fails the ishihara plate test, what is the next test that needs to be carried out
farnsworth D15
if a firefighter fails the farnsworth D15 test, what is the next test that needs to be carried out
nagel anomoloscope
which type of cone photo-pigment abnormality will not be suitable for fire fighting
protan or deutan (red or green deficiency)
what is the concept of the nagel anomaloscope
- a yellow (589nm) is matched with a mixture of red (670nm) and green (546nm)
- this is a standard RGB match but no blue primary, B is required (=zero)
what must the subject do in a nagel anomaloscope test
adjust the proportions of R and G and the brightness of the yellow
what is the indicator of someones colour vision with the nagel anomaloscope test
the chosen R/G and Y
which types of patients is the nagel anomaloscope good at idenifying
- normals
- anomalous protans and deutrans
- dichromat protans and deutrans
how is the farnsworth D15 test used
subject places 15 caps of a munsell value 5 and chroma value 4 in order
the results are plotted onto a circular diagram P, D and T the subjects makes errors along the confusion axis
which types of colour vision anomalies does the ishihara plate test detect
protan and deutan screening (either anomalous or dichromat)
what is the main justification of optometric screening of colour deficiencies
to inform the subject of their problem in time and to give appropriate advice
list 2 reasons for normal age related colour changes
- yellowing of the ocular media (nuclear cataract)
- changes in retinal sensitivity
list the non age related causes of colour deficiencies and what is affected in particular with these
arise from:
- ocular disease
- trauma
- medication
- exposure to toxic substances
- commonly affect one eye or more
- affects males and females equally
- often affects blur perception (so is easily missed in many CV tests as they mainly screen red-green defects)
