The document discusses colour vision and the physiology of colour perception. It explains that colour vision is mediated by three types of cone cells sensitive to long, medium, and short wavelengths of light. The Young-Helmholtz theory and Hering's opponent process theory are described as the two major theories of colour vision. The document outlines the retinal and cortical pathways involved in colour perception and processing. It also discusses congenital and acquired colour vision deficiencies.

2.  Colour sense is the ability of the eye to
discriminate between color excited by light of
the different wavelengths.
Or
 It is the ability to discriminate a light stimulus as
a function of its wavelength.

3.  Colour vision is a function of cones and thus
better appreciated in photopic vision.

4.  There are three different types of cones viz. red
sensitive, green sensitive and blue sensitive
which combinedly perform the function of colour
vision

5.  Colours have three attributes : hue, Intensity
& saturation.
 For any colour there is a complementary
colour that, when properly mixed with it,
produces a sensation of white.
 The colour perceived depends in part on the
colour of other objects in the visual field.

6.  A normal person can see all wavelengths
between violet to red.

7.  Blue cones retain some sensitivity at around 10
nm, but crystalline lens blocks all UV rays.
 In dim light all the colours are seen as gray, this
is called Purkinje shift phenomenon

9.  Originally suggested by Young
(1802) and subsequently modified
by Helmholtz (1866). Hence it is
called Young-Helmholtz theory.
 It postulates the existence of three
kinds of cones.

10.  The sensation of any give-
colour is determined by the
relative frequency of the
impulse from each of the
three cone systems.

11.  The red sensitive (Erythrolab) or long wave
length sensitive (LWS)
 The green sensitive (Chlorolab) or middle wave
length sensitive (MWS)
 The blue sensitive (Cyanolab) or short wave
length sensitive (SWS)

12.  The Young-Helmholtz theory conclude that the
blue, green and red are primary colour.

13.  It has been studied that the gene for:
› human rhodopsin : chromosome 3
› blue cone : chromosome 7.
› red and green cones : q arm of X chromosome.

14.  Hering proposed opponent
color theory in 1892.
 He noted that there are
some color combinations
that we never see, such as
reddish-green or yellowish-
blue.

15.  Hering hypothesized that trichromatic signals
from the cones fed into subsequent neural
stages and exhibited two major opponent
classes of processing.

16.  1. Spectrally opponent processes which were red
vs. green and yellow vs. blue.
 2. Spectrally non-opponent processes which was
black vs. white.

18.  The cone pigments like rhodopsin also
consist of 11-cis-rentinal and an opsin part
Known as photopsin.
 It is different than the opsin part of the
rhodospin.

19.  The green sensitive and red sensitive cone
pigments are very similar in Structure,
 Each of these pigments has only about 43%
homology with the opsin of blue sensitive
cone pigment.
 All the three cone pigments have about 41%
homology with rod pigment rhodospin.

20.  The principles of photochemistry of rhodopsin
can be applied to the cone pigments.
 The only difference being that the three different
types of cones are bleached by light of different
wavelength.

21.  Similar to
photochemical
changes, the
physiological 'process‘
concerned with colour
vision are also the
same as for the vision
in generals.

23.  The rods are much more sensitive.
 Cone receptor potential has a sharp onset
and offset; whereas the rod receptor
potential has a sharp onset but slow offset.

24.  Rod responses are proportionate to stimulus
intensity at levels of illumination that are below
the threshold for cones.
 cone responses are proportionate to stimulus
intensity at high levels of illumination when the
rod responses are maximal and cannot change.

25.  The receptor potential
generated in the
photoreceptors is
transmitted by electronic
conduction
 The ganglion cells
transmit the visual signal
by means of action
potential.

26.  Transmit signals horizontally in the OPL from
rods and cones to the bipolar cells.
 Their main function is to enhance the visual
contrast by causing lateral inhibitions.

27.  When a minute spot of
light strikes the retina, the
central most area is
excited but the area
around (called as
surround) is inhibited.
 Horizontal cells showed
two completely different
kinds of response.

28.  First, there was a hyperpolarizing response with
a broad spectral function termed as luminosity
(I) response, and
 second, a chromatic (c) response which was
hyperpolarizing for part of the spectrum and
depolarizing for the remainder.

29.  The bipolar cells are the first order neurons of
visual pathway.
 Recordings made from goldfish bipolar cells
showed a 'centre-surround' spatial pattern.

30.  The two different types of bipolar cells provide
opposing excitatory and inhibitory signals in the
visual pathway.
 Receptive fields of the bipolar cell is also
circular in configuration but has got a centre-
surround antagonism .

31.  The importance is, it provides a second
mechanism for lateral inhibition in addition to
horizontal cell mechanism.

32.  The exact role of these cells in colour vision is
not clear.
 Some workers have speculated that they may
act as an 'automatic colour control'

33.  It is at this level that we see first direct evidence
in the visual system for colour coding.
 There are three distinct groups of ganglion cells
designated as W, X and Y cells.
 It has been observed that colour sensation is
mediated by the 'X' ganglion cells.

34.  When all the three types of cones stimulate the
same ganglion cell the resultant signal is white.

35.  Opponent colour cell : some of the ganglion
cells are excited by one colour type cone (e.g.
red) and are inhibited by other (i.e. green) or
vice versa.
 It is concerned in the ‘successive colour
contrast’.

36.  Double opponent colour cell: these ganglion
cells have a system which is opponent for both
colour and space.
 This system is called ‘double opponent cell’
system and is concerned with the ‘simultaneous
colour contrast’.

37.  The double opponent cells have a receptive
field with a centre and surround.
 The response may be ‘on’ to red colour in the
centre and ‘off’ to it in the surround, while the
response may be ‘off’ to green in the centre and
‘on’ to it in surround.

38.  Trichromatic colour vision
mechanism extends 20-30 degrees
from the point of fixation.
 Peripheral to this red and green
become indistinguishable, and
 In the far periphery all colour sense
is lost.

39.  The very centre of
fovea (1/8 degree) is
blue blind.
 It is attributed to
chromatic aberration

40.  All lateral geniculate body neurons carry
information from more than one cone cell.
 Colour information carried by the ganglion cells
is relayed to the parvocellular portion of the
LGB.

41.  Spectrally nonopponent cells which give the
same type of response to any monochromatic
light constitute about 30 per cent of all the LGB
neurons.
 Spectrally opponent cells make 60% of LGB
neurons.

42.  These cells are excited by some wavelengths
and inhibited by others and thus appear to carry
colour information.
 These have been classified into 4 types:
1) Cells having red and green antagonism with +R/-G.
2) Cells having red and green antagonism with +G/-R.
3) Cells having blue and yellow antagonism with +B/-Y.
4) Cells having blue and yellow antagonism with +Y/-B.

43.  Colour information from the parvocelluar portion
of the LGB is relayed to the layer IV c of the
striate cortex.
 From there, the information passes to the blobs
in layers II and III

44.  The neurons in the Blobs lack orientation
specificity but respond to colours.
 Like the ganglion cells and LGB cells they are
centre-surround cells.
 Colour information is then relayed to thin strips
in the visual association area and from there to
a specialized area concerned with colour,

45.  Simultaneous colour contrast
 This phenomenon refers to perception of
particular coloured spot against the coloured
background.
 Ex: a grey spot appears greenish in a red
surround and redish in a green surround.
 It is function of double opponent cell

46.  Successive colour contrast
 It is a phenomenon of coloured after images,
 The colour of the after image tends to be near the
complementary of the primary image.
 Ex: when one sees at a green spot for several seconds
and then looks at a grey card, one sees a red spot on
the card.

47.  Phenomenon of colour constancy
 It refers to a phenomenon, in which the human eye
continues to perceive the colour of a particular object
unchanged even after the spectral composition of the
light falling on it is markedly altered.

48.  The phenomenon of hierarchy of colour coded
cells suggests a system of serial analysis of
colour sense.
 The colour coded cells have been reported to
be arranged in a hierarchy manner as follows

49.  The opponent colour cells being located in ganglion
cells and lateral geniculate neurons and
 the double opponent cells with 'centre-surround'
receptive fields in the layer IV of striate cortex.
 Complex and hypercomplex colour coded cells have
been described in the layers II, III, V and VI of the striate
cortex in the form of 'blobs'.

50.  They have been evolved on a psychological
basis and have no connection with the
physiology of eye.
 The two important colour metric systems used
internationally in industry, in printing and in the
graphic arts,

51.  This system was developed by the International
Commission of Illumination (CIE – Commission
Internal de Eclairage
 CIE colour space system is based on the
amounts of three primary colours necessary to
match a specified colour.

52.  In this system all the
colours are represented
in a cylinder in terms of
hue, value and chroma
(HVC).
 This system covers a
wide range of colours
and is thus widely used
in medicine and
industry.

53.  Hue
 i.e.dominant spectral colour
 It is determined by the wavelength of the particular
colour.
 Munsell defined hue as "the quality by which we
distinguish one color from another."

54.  Saturation
 It can be estimated by measuring how much
of a particular wavelength must be added to
white before it is distinguishable from white.

55.  Lightness or Brightness
 The lightness or brightness of a colour
depends upon the luminosity of the
component wavelength.
 In photopic vision normal eye has a
peak luminosity function at
approximately 555 nm and in scotopic
vision at about 507 nm.

57.  An individual with normal colour vision is
known as 'trichomate'.
 In colour blindness, faculty to appreciate one
or more primary colours is either defective
(anomalous) or absent (anopia). It may be
1. Congenital or
2. Acquired.

58.  Deficiency of color vision first described by
Dalton (1794), who himself was color blind;
hence the term daltonism was used in past.
 In clinical evaluation of color vision it is
important to distinguish between acquired
and congenital defects.

59. Classification
Incidence (%)
Males Females
Anomalous Trichromacy (6.3) (0.37)
Protanomaly (L-cone defect) 1.3 0.02
Deuteranomaly (M-cone
defect)
5.0 0.35
Tritanomaly (S-cone defect) 0.0001 0.0001
Dichromacy (2.4) (0.03)
Protanopia (L-cone absent) 1.3 0.02
Deuteranopia (M-cone
absent)
1.2 0.01
Tritanopia (S-cone absent) 0.001 0.003
Rod Monochromacy (no
cones)
0.00001 0.00001

60.  Dyschromatopsia, literally means colour
confusion due to deficiency of mechanism
to perceive colours.
 It can be classified into:
1. Anomalous trichromatic colour vision.
2. Dichromatic colour vision

61.  Anomalous trichromats possess three types
of photo pigment in their cones, and so are
truly trichromats.
 What makes their color vision "anomalous" is
that one pigment type is shifted along the
wavelength axis from the normal position

66.  The defect in dichromatic color vision is more
severe than in anomalous trichromacy.
 Dichromate simply lack one type of
photopigment.
 they can match any color with a mixture of only
two primaries.

67.  Complete red colour defect.

68.  Complete defect for green colour.

71.  It is an extremely rare condition presenting
as
 1.Cone monochromatism or
 2. Rod monochromatism.

72.  Characterised by presence of only one
primary colour cone and thus the person is
truly colour blind.
 Such patients usually have a normal visual
acuity and dark adaptation

73.  Rod monochromacy is an
autosomal recessive trait, it is
very rare.
 It is characterized by
 Total colour blindness,
 Day blindness (visual acuity is
about 6/60),
 Nystagmus,
 Photophobia
 Fundus is usually normal.

74.  It may follow damage to macula or optic
nerve.
 Blue-yellow impairment is seen in retinal
lesions.
 Red-green deficiency is seen in optic nerve
lesions

75.  Clinical data suggest that acquired red green
deficiencies are caused by lesions in the
ganglion cell layers, optic nerve, and visual
pathways.
 whereas acquired blue yellow deficiencies
are the result of lesions in the receptor and
outer plexiform layers

76. Condition Colour Vision Defect
Glaucoma B-Y
Retinal Detachent B-Y
Pigmentary degeneration of retina (including
retinitis pigmentosa)
B-Y
Senile macular degeneration B-Y
Myopic retinal degeneration B-Y
Chorioretinitis B-Y
Retinal vascular occlusion B-Y
Hypertensive retinopathy B-Y
Diabetic retinopathy B-Y
Papilledema B-Y
Methyl alcohol poisoning B-Y
Central serous retinopathy B-Y

77. Condition Colour Vision Defect
Optic neuritis (including retrobulbar
neuritis)
R-G
Tobacco or toxic amblyopia R-G
Leber's optic atrophy R-G
Lesions of optic nerve and pathway R-G
Papillitis R-G
Hereditary juvenile macular
degeneration
R-G
Juvenile macular degeneration R-G or B-Y

78.  After argon-laser photocoagulation there
may be hue discrimination deficiency, mostly
for blue-yellow.

79.  Many drugs are known to affect color
vision.
 Cyanopsia is associated with Sildenafil
Citrate, chloroquine, indomethacin, oral
contraceptives, antihistaminics.
 Xanthopsia is associated with the use of
cardiac glycosides.

80.  Colour blindness is present as an inherited
abnormality in Caucasian populations in about
8% of the males and 0.4% of the females.
 Tritanomaly and tritanopia are rare and show no
sexual selectivity.

81.  Colour blindness is present
in males if the X
chromosome has the
abnormal gene.
 Females show a defect only
when both X chromosomes
contain the abnormal gene.

82.  The common occurrence of deuteranomaly
and protanomaly is probably due to the
arrangement of the genes.

83.  They are located near each
other in a tandem array on
the q arm of the X
chromosome and are prone
to recombination (unequal
crossing over) during
development of the germ
cells.

84.  These test are designed for:
1. Screening defective colour vision from
normal.
2. Qualitative classification and
3. Quantitative analysis of degree of deficiency
i.e. mild, moderate or marked

85.  It is the most commonly employed test
using Ishihara’s plates.
 It is quick method of screening colour
blinds from the normals.

86.  Another test based on the same principle is
Hardy-Rannd-Rittler plates tests (HRR).

87.  In this test, the subject has to name the
various colours shown to him by a lantern
and the judgment is made by the mistake he
makes.
 Edridge-Green lantern is most popular.

88.  It is spectroscopic test in which
subject has to arrange the
coloured chips in ascending
order.
 The colour vision is judged by
the error score, i.e. greater the
score poorer the colour vision.

89.  It is a miniature
version of the 100-hue
test, consisting of 15
caps that form a color
circle.

90.  It is also a
spectroscopic test
where a central
coloured plate is to
be matched to its
closest hue from four
surrounding colour
plates.

91.  In this test the
observer is asked to
mix red and green
colours in such a
proportion that the
mixture should match
the given yellow
coloured disc.

92.  In this the subject is
asked to make a series of
colour-matches from a
selection of skeins of
coloured wools.

93.  All children at an early age. Testing should be
performed prior to the first grade.
 All patients on their first office visit
 All patients with an undiagnosed low visual
acuity.
 All patients who report recent color
disturbances or differences between the eyes.

94.  Hereditary color-vision defects are constant
throughout life, and these defects cannot be
cured.
 it is possible to improve discrimination of some
colors with the use of red filters.

95.  Many color defectives cannot distinguish reds
and oranges from greens and browns. A red
filter often enables these people to make these
distinctions.

97.  A.k. khurana anatomy n physiology
 Adlers physiology
 Duanes Ophthalmology
 Internet