Presenter: Dr.Parth Satani Moderator: Dr.Prakash Chipade

Colour vision and its clinical aspects

Colour vision &clinical aspectIntroduction Theories of colour vision Neurophysiology of colour vision Phenomenon associated with colour vision Normal colour attributes Colour blindness Colour vision tests Management of colour blindness

IntroductionColour vision is the ability of the eye to

discriminate between colours excited by lights of different wavelengths.

Colour vision is a function of cone . Better appreciated in photopic condition

Theories of colour vision

Trichromatic theorySuggested by Thomas Young and

HelmholtzIt postulates the existence of three

kinds of conesEach cone containing a different

photopigment and maximally sensitive to one of three primary colours i.e. Red, Green and Blue.

Trichromatic theoryAny given colour consist of

admixture of the three primary colour in different proportion

RED SENSITIVE CONE PIGMENT – (Erythrolabe or long wavelength sensitive cone pigment): It absorbs maximally in a yellow position with a peak of 560 nm. But its spectrum extends far enough in to the long wavelength to sense red.

Trichromatic theory GREEN SENSITIVE CONE PIGMENT –

(Chlorolabe or medium wavelength sensitive cone pigment): It absorbs maximally in the green portion with peak at 530 nm.

BLUE SENSITIVE CONE PIGMENT (Cyanolabe or short wavelength sensitive (SWS) cone pigment): absorbs maximally in the blue – violet portion of the spectrum with a peak at 415 nm

Neitz M, Neitz J, Jacobs GH. Spectral tuning of pigments underlying red-green color

vision. Science 1991; 252:971–974.

Opponent TheoryEwald Heringsome colours are mutually exclusiveThe cone photoreceptors are linked together to form

three opposing colour pairs: blue/yellow, red/green, and black/white

Activation of one member of the pair inhibits activity in the other 

No two members of a pair can be seen at the same location to be stimulated

Never "bluish yellow" or "reddish green“colour experienced

The trichromatic theory by itself was not adeqaute to explain how mixture of lights of different colours could produce lights and yet another colour or even to appear colorless. So both the theories are useful in that. The colour vision is trichromatic at the

level of photoreceptor and Opponent theory is explained by

subsequent neural processing.

Photochemistry Cones differ from rods only in opsin part c/a

photopsin

The green sensitive and red sensitive cone pigments- 96% homology of amino acid sequence

Where as red or green photopigment have only about 43% homology with the opsin of blue sensitive cone pigment

All three bleached by light of different wavelength

Neurophysiology

Genesis of visual signal- The photochemical changes in cone pigments is followed by a cascade of biochemical change cone receptor potential.Cone receptor potential has sharp onset and sharp offset Rod receptor potential has sharp onset and slow offset

Processing and Transmission of colour vision signals Action potential generated in

photoreceptors

Bipolar cells and horizontal cells

Ganglion cells and amacrine cells

Horizontal Cell

It shows two complete different kind of response.Luminosity Response : hyperpolarising

response.

Chromatic Response : hyperpolarizing in a part of spectrum and depolarising for the remainder of the spectrum.

Horizontal cellsFirst stage in visual system where evidence of

chromatic interaction has been found wavelength discrimination of spectrum occur at

this level.

Bipolar cells

1. Show centre surround spatical pattern. 2. Red light striking in the centre of this cell

causes hyperpolarisation 3. Green light in the surrounding causes

depolarization.

Amacrine cells The exact role is not known but they

may act as an automatic colour control.

Ganglion cells three types- W, X and Y X ganglion cell mediate the color sensation. A single ganglion cell may be stimulated by a

number of cones or by a few cones.When all the three types of cones (Red, Green

and Blue) stimulate the same ganglion cell the resultant signal is white

Ganglion cells

Some of the ganglion cells are excited by one colour type cone and are inhibited by other.

Opponent colour cell system Concerned in the successive colour

contrast.

Phenomena associated with colour senseSuccessive colour contrast:Phenomena of colour after imageAs a general rule colour after image tends

to be near the complementary of the primary image

when one see at a green spot for several seconds and then looks at a grey card one see red spot on the card.

Ganglion cellsThese ganglion cells have a system which is

opponent for both colour and space-‘Double opponent cell system’

Concerned with the simultaneous colour contrast.

For example response may be ‘on’ to red 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.

off on

Phenomena associated with colour senseSimultaneous colour contrast:Colour of the spot tends to be towards

the complementary of the colour of surround

So grey spot appears greenish in a red surround and reddish in a green surround

Phenomena associated with colour senseColour constancy:In which the human eye continue to

perceive the colour of a particular object unchanged even after the spectral composition of the light falling on it is markedly altered.

Computational mechanism of brain is responsible for this phenomenon.

Luminance mechanism

+-

Red-green opponent mechanisms

(S+L)-M=RED M-(S+L)=GREEN

• ON-center ganglion cell receiving input from an M cone center with S and L cones in the surround would provide

M-(S+L)–green• This same receptive field through an

OFFcenter ganglion cell produces (S+L)-M–red

Blue-yellow opponent mechanism

(S+M)-L=BLUE L-(M+S)=YELLOW

• An L cone center with an M and S surround would result in L-(S+M)–yellow

• This same receptive field through an OFF-center ganglion cell produces (S+M)-L–blue

Distribution of colour vision in the Retina Extend 20-30 degrees from the point of

fixationPeripheral to this red and green become

indistinguishableCenter of fovea is blue blind.

Processing of colour signals in lateral geniculate body

Colour information carried by ganglion cell is relayed to the parvocellular portion of LGB.

Spectrally non opponent cell which give the same type of response to any monochromatic light constitute about 30% of all the LGB neurons.

Spectrally opponents cells make 60% of LGB neurons these cells are excited by some wavelength and inhibited by others and thus appear to carry colour information

Visual cortex Colour information

parvocellular portion of the LGBlayer IVc of striate cortex (area 17)

blobs in the layers II and IIIthin strip in the visual association area

lingual and fusiform gyri of occipital lobe

.

Colour attributes

HUE: identification of colour,dominant spectral

colour is determined by the wavelength of particular colour

Brightness: intensity of colour,it depends on the

luminosity of the component wavelength. In photoptic vision-peak luminosity function at

approximately 555 nm and in scotopic vision at about 507 nm.

Colour attributesThe wavelength shift of

maximum luminosity from photoptic to scotopic viewing is called ‘ Purkinje Shift Phenomenon’

So in dim light all colour appear grey

Colour attributes

SATURATION : it refers to degree of freedom to

dilution with white.It can be estimated by measuring how

much of a particular wavelength must be added to white before it is distinguishable from white.

The more the wavelength require to be added to make the discrimination, the lesser the saturation.

Colour blindness Colour blindness is also called  “Daltonism” Defective perception of colour -anomalous and

absent of colour perception is anopia It may be-

Congenital Acquired

Type of colour blindnessMonochromacy --Total colour blindness -- when

two or all 3 cone pigments are missing [ very rare ]

A] Rod monochromacy B] Cone monochromacy Dichromacy - When one of the 3 colour pigment

is absent 1. Protanopia - RED retinal photoreceptors

absent [Hereditary, Sex linked, 1% ]2. Deuteranopia -GREEN retinal photoreceptors

absent [ Hereditary, Sex linked ]3. Tritanopia -BLUE retinal photoreceptors

absent

Type of colour blindness TRICHROMACY [Anomalous Trichromacy]

Colour vision deficiency rather than loss 1. Protanomaly - RED colour deficiency

[Hereditary, Sex linked, Male1%, ]2. Deuteranomaly - GREEN colour

deficiency[Hereditary, Sex linked, Male 5% ]

3. Tritanomaly - BLUE colour deficienc [ Rare,Not hereditary ]

Genetics of colour blindnessPhotopigments, are composed of an

apoprotein and 11-cis retinal chromophoreGenes OPN1LW, OPN1MW, and OPN1SW,

each encode an apoprotein(termed opsin)chromophore is a vitamin A derivative that

absorbs ultraviolet light,when covalently bound to an opsin the

chromophore absorption spectrum is shifted to longer wavelengths.

Genetics of colour blindnessGene location defect reason

OPN1MW Xq28 deutan Absence or lack of expression

OPN1LW Xq28 protan Absence or lack of expression

OPN1SW 7q32.1 tritan Missence mutation

Nathans J, Thomas D, Hogness DS. Molecular genetics of human color vision: the genes encoding blue, green, and red pigments. Science 1986; 232:193–202.

Pattern of inheritanceGene rhodopsin - chromosome 3.Gene for blue sensitive cone -

chromosome 7The genes for red and green

sensitive cones are arranged in tandem array on the ‘q’ arm of x chromosome so defect is inherited as x- linked recessive

Tritanopia is inherited as an autosomal dominant defect,

Congenital colour blindnessCongenital colour blindness is two type

1. Achromatopsia2. Dyschromatopsia

More comman in male (3-4%)than female(0.4%)

It is x-linked recessive inherited condition.

AchromatopsiaCone monochromatism:

1. Presence of only one primary colour 2. So person is truely colour blind

Rod monochromatism: Complete or incomplete Inherited as autosomal recessive trait

1. Total colour blindness2. Day blindness(visual acquity is about 6/60)3. Nystagmus4. Fundus is normal

Type of colour vision blindness

Acquired colour blindnessAny disease affecting the photoreceptors,optic

nerve fibres can affect colour perception of an individual.

Koellner’s rule* - damage of the retina induces a tritan defect, and damage of the optic nerve induces a red-green-defect

Type 1 red-green- Similar to a protan defect, Progressive cone dystrophies( e.g. Stargardt’s

disease*),

Type 2 red green- Similar to a deutan defect;Optic neuropathy (e.g.retrobulbar neuritis

associated with multiple sclerosis)Ethambutol toxicity

Type 3 blue(Most common)(with reduction of luminous efficacy)Progressive rod dystrophies ,Retinal vascular lesions, Peripheral retinal lesions

(e.g. retinitis pigmentosa,diabetic retinopathy,Glaucoma)

Type 3 blue [With displaced relative luminous efficacy to shorter wavelengths (pseudoprotanomaly)]

Macular oedema(e.g. central serous, retinopathy, diabetic

maculopathy, age-related macular degeneration)

Verriest G. 1963. Further studies on acquired deficiency of color discrimination. J Opt Soc Am 53:185-195.

Drug causing colour blindnessRed-Green DefectsAntidiabetics (oral), TuberculostaticsBlue-Yellow DefectsErythromycin,Indomethacin,Trimethadione,Chlor

oquine derivatives ,Phenothiazine derivatives,sildenafil

Red-Green and/or Blue-Yellow DefectsEthanol,Cardiac glycosides (Digitalis,

digitoxin),Oral contraceptives

LyleWM. 1974. Drugs and conditions which may affect color vision, part I-drugs and chemicals. JAm Opt Assoc 45:47-60.

Tests for colour visionScreening tests: Identifies subjects with normal

and abnormal colour vision. Grading tests: Estimates severity of colour

deficiency.Classifying tests: Diagnose the type and

severity of colour deficiencyVocational tests: Identifies colour matching

ability,hue discrimination and colour recognition.

Colour vision & principle function

Dain SJ. Clinical colour vision tests. Clin Exp Optom 2004 87:276-93.

Type of colour vision testPseudoisochromatic (PIC) plate tests Most commonly used tests, Easily and rapidly administered. Designed to screen for the presence of red-green

inherited color vision defects.1. Ishihara Plates2. American Optical Hardy-Rand-Rittler Plates3. Standard Pseudoisochromatic plates4. City University test

Ishihara testComes in three different forms: 16 plates, 24

plates, and 38plates.(10th edition)Plates should be held at 75 cm under good

illumination .Numerals should be answered in not more

than 3 secPathway tracing should be completed within

10 sec.Designed in four ways

1st plate- for demonstration and malingerers

Transformation plate2-9 plates

A number seen by a colour normal appear different to colour deficient subject.

Vanishing platePlate no. 10-17th

A number is seen by a colour normal but cannot be seen by a colour deficient subject.

• (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.

Out of initial 21 plates, if 17 or more plates are read correctly by an individual his colour sense should be regarded as normal.

If 13 or less plates are correctly read then the person has a red-green colour defect.

Plates 22 to25 are for differential diagnosis of Protans and Deutans.

Disadvantage of this test is that it neither test for tritanope nor grade the degree of deficiency

Birch J. Efficiency of the Ishihara plate for identifying redgreen colour deficiency. Ophthal Physiol Opt 1997; 17:403-8.

American optic hardy rand ritterThere are plates with paired vanishing designsContain geometric shapes (circle, cross and triangle)Shape is in neutral colours on a background matrix of

grey dots.Six plates for screening (four red-green and two tritan),10 plates for grading the severity of protan and deutan

defectsFour plates for grading tritan defectsIdeal for paediatric testing of congenital colour

blindness

CITY UNIVERSITY COLOUR VISION TEST10 Plates ,35 cm,daylight,right angle.Where a centre coloured plate is to be matched to its

closest hue from four surrounding colour plates.Three peripheral colours are typical isochromatic

confusions with the central colour in colour deficiency.

The fourth colour is an adjacent colour in the D15 sequence and is the intended normal preference

Identifies moderate and severe colour deficiency only.

Arrangement test Easily administered Useful for both inherited and acquired color defects. Results permit diagnosis of the type of defect, and

may be analyzed quantitatively for assessment of severity.

1. Farnsworth-Munsell 100 hue test2. Farnsworth-Munsell Dichotomous D-15 or Panel

D-15 test3. Lanthony Desaturated D-154. Adams Desaturated D-15

FARNSWORTH- MUNSELL 100 HUE TEST:Very sensitive reliable and effective

method of determining colour vision defect.

The test consists of 85 movable colour samples arranged in four boxes of 22 colours

Subject has to arrange 85 colour chips in ascending order.

The colour vision is judged by the error score.

The results are recoded in a circular graphThe Farnsworth-Munsell Hue Test Scoring Software

has been developed to speed up and simplify scoring of the FM 100 Hue test and to provide a powerful set of analytical and administrative tools

FARNSWORTH- MUNSELL D-15 HUE TEST –

Abridged versionPatients are asked to

arrange 15 coloured caps in sequential order based on similarity from the pilot colour cap

Intended for screening color vision defects only.

Used to detect color vision defects such as red-green and blue-yellow deficiencies as opposed to color acuity.

HOLMGREN’S WOOL TEST

The subject is asked to make a series of colour matches from a selection of skeins of coloured wools.

Spectral anamaloscope

Accepted as the most accurate for diagnosisunlike most other tests,they require a fair amount of

skill on the part of the examiner.1. Nagel anomaloscope2. Oculus HMC (Heidelberg Multi Colour)

anomaloscope3. Neitz anomaloscope4. Pickford-Nicolson anomaloscope

NAGEL’S ANAMALOSCOPE

GOLD STANDARD Extraordinarily sensitive. In this test the observer is asked to mixed red and green

colours in such a proportion that the mixture should match the yellow colour disc.

Indication of defect is relative amount of red and green required.

The mixture fieldUpper half of the bipartite fieldComposed of a mixture of two wavelengths - 670 nm (red)

and 546 nm (green)Patient adjusts the relative mix of these two colors using a

control knob that ranges from a value of 0 for pure green to 73 for pure red.

Total luminance remains constant for all mixture settings. For a normal trichromat (with normal a V(λ) function), the

brightness will appear constant for all settings.

The test field Lower half One fixed wavelength - 590 nm (yellow) light Luminance is adjustable from a scale of 0 (dim) to 35

(bright) Protanope match either a 546-nm or 670-nm light to a 590-

nm light by adjusting their relative brightnessesDeuteranope can also be fooled into incorrectly matching

those hues with 590-nm without much change in brightness

Consider deuteranomalous trichromats as being “green-weak.” to compensate, they will tend to add more green to the mixture than normal.

Consider protanomalous trichromats as being “red-weak.” To compensate, they will tend to add more red to the mixture than normal.

As described above, protans will make abnormal brightness settings.so it helps to differentiate between protanomalous versus deuteranomalous trichromats.

Graphic representation of diagnostic results obtained with the nagel anomaloscope showing different matching ranges and yellow luminance values in protan and deutan colour deficiency

Occupational testssame as those used clinically (PIC and arrangement

tests), special tests designed for particular vocational

requirements.Lantern test

1. Edridge-Green Lantern2. Farnsworth Lantern3. Holmes-Wright Lantern4. Martin Lantern

LANTERN TESTVocational tests to select applicants for occupations in

the transport industries that required signal-light identification

The test is performed in a dark room at 6 meters distanceIt has five rotating discsDisc 1 – aperture sizes varies 1.3 to 13 mm.Disc 2-4 – Eight colour filters (2 red, 2 green, white,

yellow, blue, Purple)

Fransworth lantern Edridge green lantern

Disc 5 – a clear aperture, 5 neutral density filters, a ribbed glass

(simulate rain), frosted glass (simulate mist)Recommendations of the test state that a candidate

should be rejected if he calls: Red as Green Green as Red White light as Green or Red or vice versa Red-Green or White light as black

Duke-Elder S. Congenital colour defects. In: System of Ophthalmology. 2nd ed. London: Henry Kimpton; 1964. p.661-8.

Treatment of colour blindnessIdeally there is no treatment but can help person by Colour blind person can see properly using a special

version of Adobe Photoshop.

There are special Monitors for Colour Blind people

There are smart phones with a software,when seen through their camera shows the actual colours the way a normal person would see

Red Green Colour Blind people can not see 3D movies which use Red and Green filters but can see recent 3D movies which are devised to be seen with glasses using crossed Polaroid lenses

X-chrome lens is a monocular (non-dominant)contact lens which significantly enhance colour perception,

colormax lenses are tinted prescription spectacle lenses intended as an optical aid for people with red-green colour vision deficiency

Do not help wearer to percieve or appreciate colour like normal person but merely add brightness/darkness differences to colour.

Some filters 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

Gene therapyIt is experimental aiming to convert congenitally

colour blind to trichromats by introducing photopigment gene

As of 2014 there is no medical entity offering this treatment

No clinical trial available for volunteers.

Thank you