2. The normal human retina contains two kinds of light
sensitive cells: the rod cells (active only in low light) and
the cone cells (active in normal daylight and responsible
for color perception).
The different kinds of inherited color blindness result from partial or
complete loss of function of one or more of the different cone
systems.
3. ColorVision
Is the ability of the eye to discriminate
between colours excited by light of different
wave lengths.
Color Blindness
Is the inability to perceive difference between
some of the colours that other people can
distinguish.
4. Normally, there are three kinds of
cones (each one sensitive to a
specific range of wavelengths):
L(Long) ---"red" cones (64%)
(725 – 647 nm, peak : 565 nm)
M(Middle) ---"green" cones (32%)
(575 – 492nm, peak : 535 nm)
S(Short) ---"blue" cones (2%)
(492 – 450 nm, peak : 420 nm)
5. Trichromatic theory: Also called as young helmholtz
theory:
It postulates the existence of three kinds of cones
Each cone containing a different photopigment
and maximally sensitive to one of three primary
colours i.e. Red, Green and Blue.
6. Monochromacy: occurs when two or all three of the cone pigments
are missing and color and lightness vision is reduced to one
dimension.
Total color blindness
Dichromacy: occurs when only one of the cone pigments is missing
and color is reduced to two dimensions.
Partial color blindness
red-green
blue-yellow
7. Also known as rod monochromacy, complete achromatopsia,
and
typical monochromacy.
A rare, non-progressive inability to distinguish any colors as a
result of absent or nonfunctioning retinal cones.
See everything as white, black, or some shade of gray
Typically caused by a missense mutation (a switched amino
acid)
in the CNGB3 gene.
8. CONGENITAL DEFECTS ACQUIRED DEFECTS
1 Affects both eyes equally 1 May affect one eye only or asymmetric
2 Usually a R-G defect is found 2 B-Y or R-G defect
3 Other visual functions normal 3 Other visual functions also abnormal
4 Stable through out life time 4 Variable, depend on test and diseases
conditions
5 Learned to adapt- can label objects 5 Cannot name color correctly
6 More prevalent in male 6 Equally Prevalent in male and female
7 One or more Cones are absent 7 Cones are present but work at
decreased/altered spectral sensitivity
8 Causes: X-linked recessive gene 8 Causes: diabetes, glaucoma,
medication, aging, and Chemical
Exposure
9. The objectives of assesment of color vision is
to:
Screen for color deficiency.
grade the severity of color vision defect.
Classify the type of defect.
10. PSEUDOISOCHROMATIC
COLOUR TEST:
most commonly employed
tests- eg.-
ISHIHARA PLATES
and
HRR(HARDY,RAND,RITTLER)
plates
Ideal for paediatric testing of
congenital color blindness.
11. designed in four ways
1st
plate-
for demonstration and
malingerers.
12. (2-9) plate- Transformation
plates: normal person sees one
figure and a CVD sees another.
(10-17)plate-Vanishing
plates: normal person see the
figure while a CVD person will
not.
13. Pseudoisochromatic colour
plates
(18-21)plate-Hidden-digit
plates: normal person does not
see a figure while a CVD will see
the figure.
(22-25)plate-Diagnostic
plates: seen by normal
subjects, CVD one number
more easily than another.
Protans only see the no. on the
right side and deutans only see
the no. on the left.
Should be used at 75 cm, day
light, right angle to visual axis, 3
sec time.
14. It is a hue
arrangement type
test.
Patients are asked to
arrange 15 coloured
caps in sequential
order based on
similarity from the
pilot colour cap at a
distance of 50 cm.
15. Currently No treatment.
Some filters (goggles/tinted contact lenses) may
help to distinguish the colours but not in the
identification of colours.
The purpose of this is to eliminate certain lights and
modify the light reaching the eyes so that the
receptors receive correct information.
