2. 2
Retinal Cones–Normal Color Vision
Red cones
Green cones
Blue cones
Brightness = R + G
Color = R – G
Color = B – (R+G)
Red cones
outnumber green
cones 2/1
Red + Green cones
outnumber blue
cones 10/1
Blue cones
absent in
central
fovea
3. 3
Retinal Cones–Normal Color Vision
Red, green and blue cone sensitivity vs.
wavelength curves
4. Types of Color Vision Deficiencies
• Trichromacy (“three-color vision”)
– Normal Color Vision
1) Congenital colour blindness
a) Dyschromatopsia
• Anomalous Trichromacy (“unusual three-color vision”)
– See all three primary colors.
– One color is seen weakly
• Protanomaly (L-cone defect) red-weak
• Deuteranomaly (M-cone defect) green-weak
• Tritanomaly (S-cone defect) blue-weak
• Dichromacy (“two-color vision”)
– See only two of the three primary colors
– One type of cone is totally absent or nonfunctional.
• Protanopia (L-cone absent)
• Deuteranopia (M-cone absent)
• Tritanopia (S-cone absent) 4
5. b) Achromatosia
• Cone monochromatism
only one primary colour.
• Rod Monochromatism
(no cones at all) (“no-color vision”)
Sees no colors, only shades of gray
Day blindness (VA 6/60)
Fundus usually normal
5
7. 2) Acquired colour blindness
• Blue-yellow impairment
retinal lesions
• Red-green impairment
optic nerve lesion
• Blue colour defect
old age
7
8. 8
What happens in hereditary
color deficiency?
Red or green cone peak
sensitivity is shifted.
Red or green cones absent.
9. 9
533 nm
437 nm 564 nm
B G R
NORMAL CONE SENSITIVITY CURVES
(TRICHROMAT)
10. 10
437 nm 564 nm
B G R
Deuteranomaly
(green shifted toward red)
5% of
Males
11. 11
437 nm 564 nm
B G R
Deutan Dichromat
1% of
Males
(no green cones; only red and blue)
12. 12
1% of Males (there is no green
curve)
437 nm 564 nm
B R
Deutan Dichromat
(no green cones; only red and blue)
13. 13
437 nm
533 nm
B G R
Protanomalous
(red shifted toward green)
1% of
Males
14. 14
437 nm
533 nm
B G R
Protan Dichromat
1% of
Males
(no red cones; only green and blue)
15. 15
1% of Males (there is no red
curve)
437 nm
533 nm
B G
Protan Dichromat
(no red cones; only green and blue)
16. 16
Why do colors that
look different to us
appear the same to
color deficient
individuals?
17. 17
Large
Consider a green vs.
yellow light…
difference in
stimulation of
green and red
cones
Small
difference
in
stimulation
B G R
Color Normal Individual
The two spots
appear
different in
color because
R-G is large
for one, and
small for the
other.
18. 18
Each spot produces the same R-G stimulation
and thus looks the same!
Small
difference
in
stimulation
B G R
Small
difference
in
stimulation
Deuteranomaly
Look the same!
(the green sensitivity curve is shifted toward the red)
19. 19
Hereditary Color Deficiency
8-10% of males and 1/200 females (0.5%) are
born with red or green color deficiency.
Sex-linked recessive condition (X chromosome).
Protanomaly—red cone peak shifted toward
green (1%)
Protan Dichromat—red cones absent (1%)
Deuteranomaly—green cone peak shifted
toward red (5%)
Deutan Dichromat—green cones absent (1%)
Hereditary tritan defects are rare (0.008%)
21. Tests for colour vision
• Pseudo-isochromatic chart test
• Lantern test
• Fansworth munsell 100 hue test
• Nagel’s anomaloscope
• Holmgren’s test
21
23. How to use the test
The plates are designed to be appreciated correctly in a room
which is lit adequately by daylight.
The introduction of direct sunlight or the use of electric light may
produce some discrepancy in the results because of an
alteration in the appearance of shades of color.
When it is convenient only to use electric light, it should be adjusted
as far as possible to resemble the effect of natural daylight.
The plates are held 75 cm. from the subject and tilted so that the
plane of the paper is at right angles to the line of vision.
24. • The correct position of each plate is indicated by
the number which is printed on the back of the
plate.
• The numerals which are seen on plates 1-17 are
stated, and each answer should be given without
more than three seconds delay.
• If the subject is unable to read numerals, plates
18-24 are used and the winding lines between the
two X’s are traced with the brush.
• Each tracing should be completed within ten
seconds.
25. • It is not necessary in all cases to use the whole series of
plates.
• Plates 16 and 17 may be omitted if the test is designed
merely to separate the color defectives from those with
normal color appreciation.
• In a large scale examination the test may be simplified to an
examination of six plates only;
– No 1,
– one of the Nos 2, 3,
– one of Nos 4, 5, 6, 7,
– one of Nos 8, 9,
– one of Nos 10, 11, 12. 13 and
– one of Nos 14, 15.
• It may be necessary to vary the order of the plates if it is
suspected that there is a deliberate decetion on the part of
the subject
32. Plate no. Normal
person
RED-GREEN
Deficient
Total colour
blind or
weakness
1 12 12 12
2 8 3 X
3 29 70 X
4 5 2 X
5 3 5 X
6 15 17 X
7 74 21 X
8 6 X X
9 45 X X
10 5 X X
11 7 X X
12 16 X X
13 73 X X
14 X 5 X
15 X 45 X
33. Protan Deutan
strong mild strong mild
16 26 6 (2) 6 2 2 (6)
17 42 2 (4) 2 4 4 (2)
The mark X shows that the plate cannot be read.
Blank spce denotes that the reading is indefinite.
The numerals in parenthesis show that they can be read but they are
comparatively unclear.
34. Analysis of the results
• As assessment of the readings of plates 1 to 15
determines the normality or defectiveness of color
vision.
• If 13 or more plates are read normally, the color vision is
regarded as normal.
• If only 9 or less than 9 plates are read normally, the
colour vision is regarded as deficient.
• However, in reference to plates 14 and15, only those
who read the numerals 5 and 45 and read them easier
than those on plates 10 and 9 are recorded as abnormal
readings.
35. • It is rare to find a person whose recording of normal
answers is 14-16 plates.
• An assessment of such a case requires the use of other
colour vision tests, including the anomaloscope.
• In the assessment of color appreciation by the short
method involving 6 plates only as described on page 4,
a normal recording of all plates is proof or normal color
vision.
• If there is a discrepancy in any of the recordings, the full
series of plates should be used before diagnosing a red-green
deficiency.
36. Nagel’s anomaloscope
36
The Nagel anomaloscope is the gold
standard.
Advantages: test has a long and
hallowed
history that is well respected.
Disadvantages: expensive instrument
that
requires an experienced examiner’s
skills.
Validity: validation measures of other
colour
vision tests are based on this instrument.
Calibration: requires spectroscope to
calibrate.
37. Farnsworth-Munsell 100 Hue
Test (FM-100)
In its present form, the test consists of eighty-five
caps in four boxes, used one box at a time.
There are no confusion colours in a box and therefore the
test is a hue discrimination metric.
The caps are in equal steps of hue around a hue
circle.
37
38. • The results are quantitative, can be subjected
to age correction, and are amenable to
statistical evaluation.
• Validity - since this is the only test of its sort
(hue discrimination) cross validation with other
metrics is not possible.
• The test has become the second gold standard
for assessing a wide variety of hereditary and
acquired conditions
38
39. The City University test TCU
• Procedure
- Test is done at 35 cm at day light at right angle of
the visual plane.
- It consists of 10 plates each contains four peripheral
colored dots with one on the centre.
- The patient is asked to select the peripheral that most
closely matches the central one
- Results are written as Top(T), Bottom (B),Right
(R),Left (L) and score paper is present to analyze
defect due to patient response.
41. • The patient had to match one piece of wool to the samples in the box in
this colour blindness test.
• There are light and dark shades to confuse the patient. This helped
detect problems.
• The numbers on the pieces of wool were codes.
• Swedish Holmgren's coloured wool test for colour blindness, Europe,
1871-1900 physiologist Alarik Frithiof Holmgren (1831-1897) devised this
test in 1874.
• He pursued his investigations following a railway accident in Sweden in
1876.
• The accident was believed to be caused by a colour blind train driver.
• Following Holmgren’s research, colour blindness tests were made
compulsory for railway and shipping workers in Sweden.
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