Humans have a trichromatic system. Explain that.
3 variants of photoreceptors
Higher number of rods, fewer cones
Cones- Blue (S), Red (L), Green (M)
At which wavelength doesphotopic spectral sensitivity peak? What is the result?
555nm - photopic, 505nm- scotopic
red and green cones overlap
we are more sensitive to green- yellow light
what are the 2 types of CVD. Describe them
Describe CV genetics.
If female (XX) carrier mates with normal man(XY)?
If CV male mates with carrier woman?
if father is colour blind and mother is normal?
Daughters are carriers.
What is rod and cone monochromacy?
There are 2 types of congenital CVD. Describe them.
What are the prefixes for each con CVD and how common are they
There's 2 types of CV testing; Screening and Diagnosis. describe each
Which are the screening tests and diagnosis test
Describe the Ishihara Test
based on pseudoisochromatic plates
simple, easy and quick
24/38 plates
at 75cm
allow 4s per page
examiner holds book
instruction “if you can see a number can you tell mee what it is”
Identifies R/G con defects- no good for tritanopia
cant differentiate btwn dichromats and anomalous trichromats
Describe the City University Test ( TCU)
if screening plates are pssed, omit diagnostic plates
35/40cm
Screening plates- “for each grp of 3 dots, are they all the same coolour or does one dot appear different”
one error is allowed ( 9/10)
Diagnostic plates- “ Looking at the central dot, which of the 4 surrounding dots is most similar in colour"
Ishihara vs City Test
Ishihara- picks up more deficiences BUT more false positives
Ishihara- good at protan vs deutan
City- picks up fewer deficiences BU more false negatives
City- picks up titan defects + useful for acquired defects
City- less good at differentiating btwn P,D,T
Who to test for CVD
Describe the D15 test
16 coloured caps, arranged in colour order
close lid, flip box over and record number number sequence on chart
lines will confirm whether defect is P,D or T
doesnt seperate dichromats and trichromats
Farnsworth- Munsell 100-Hue Test
4 boxes of 23 coloured caps
px arranges in colour sequences, box flipped over and sequence recorded
score plotted is numerical difference btwn adjacent caps on each side
higher total score= more severe deficiency
Which test do you use to diagnose btwn dichromats and trichromats
nagal anomaloscope
How do patients with CVD differentiate btwn colours?
contrast
objects of knon colour
comparing colours
tinted specs/cl worn in 1 eye to allow colour comparisons ( Chromagen lenses)
is colour vision a necessity for drivers?
NO
can guess traffic light colours by their position
redbrake lights a problem with protanopia
road signs are high contrast so no problem
Can px with CVD do duochrome test?
yes, it depends on longitudinal chromatic abberations
both colours appear similar so tell px “dont worryabout brightness of background, just tell me which side do the targets look clearer”
CVD affects hobbies and sports like…?
snooker ( allowed to ask ref what colour ball is if declared CVD)
football
gardening
choosing food/clothes
telling if food is cooked, fruit is ripe
remote console needs to be recharged or not
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