aravind eye care system a r a v i n d e y e h o s p i t a l & postgraduate institute of...

ARAVIND EYE CARE SYSTEM

A R A V I N D E Y E H O S P I T A L& Postgraduate Institute of

OphthalmologyMadurai, India

ARAVIND EYE CARE SYSTEM

A R A V I N D E Y E H O S P I T A L& Postgraduate Institute of

OphthalmologyMadurai, India

Colour visionColour vision

P.S.SelvakumarP.S.SelvakumarFaculty Faculty

Aravind School of OptometryAravind School of Optometry

A R A V I N D E Y E C A R E S Y S T E MA R A V I N D E Y E C A R E S Y S T E M

What is colour vision?What is colour vision? An ability to distinguish certain colors.An ability to distinguish certain colors.

Presents only in day light / bright light conditions & Presents only in day light / bright light conditions & absent at night / dark.absent at night / dark.

Maximum sensitive color cones are considered.Maximum sensitive color cones are considered.

Normal person can match the 3 primary colors with all Normal person can match the 3 primary colors with all spectral hues called, spectral hues called, Trichromatic.Trichromatic.


Light sensitive receptorsLight sensitive receptors Rods (120 million)Rods (120 million)

Located in peripheral retina.Located in peripheral retina.

Responsible for night vision.Responsible for night vision.

Cones ( 7 million)Cones ( 7 million) Responsible for color vision ,day vision and sharper vision.Responsible for color vision ,day vision and sharper vision.

Located around fovea region.Located around fovea region.


Types of conesTypes of cones Red, Blue and GreenRed, Blue and Green

74% red cones.74% red cones.

16% blue cones.16% blue cones.

10% green cones.10% green cones.

Color discrimination occurs through the integration of all Color discrimination occurs through the integration of all cones.cones.

Yellow perceives from red and green combination.Yellow perceives from red and green combination.

White perceives from inputs of all cones.White perceives from inputs of all cones.


Color vision defects / deficienciesColor vision defects / deficiencies

Due to absence / defects of cones. Due to absence / defects of cones. Unable to interpret the signals to brain.Unable to interpret the signals to brain. Classified as either hereditary or acquired.Classified as either hereditary or acquired. Affects about 8% of men & 0.5% women.Affects about 8% of men & 0.5% women. Abnormal color matching and color confusions Abnormal color matching and color confusions

may be result.may be result. Grass may appear in orange color.Grass may appear in orange color.


Types of color vision defectsTypes of color vision defects

TrichromaticTrichromatic – all cones present – normal vision. – all cones present – normal vision.

DichromaticDichromatic – one cone completely absent – one cone completely absent

MonochromaticMonochromatic – only one cone present. – only one cone present.

Achromatic – no functioning cones. – no functioning cones.


Dichromacy Dichromacy Two cone receptors for matching with all spectral hues. Two cone receptors for matching with all spectral hues.

Three types.Three types.

Red and green defects Red and green defects Are sex-linked. Are sex-linked.

Protanopes - lack of red receptors.Protanopes - lack of red receptors.

Deutranopes – lack of green receptors.Deutranopes – lack of green receptors.

Blue and yellow confusion due to Blue and yellow confusion due to Tritanopes – lack of blue receptorTritanopes – lack of blue receptor

CIE Chromaticity diagram useful to identify dichromats.CIE Chromaticity diagram useful to identify dichromats.


Protanopia Protanopia Red (erytholabe) is absent and replaced by green (chlorolabe).Red (erytholabe) is absent and replaced by green (chlorolabe).

Protanopes confuses red and green.Protanopes confuses red and green.

Blue become less saturated until 492nm,as wavelengths Blue become less saturated until 492nm,as wavelengths increases. (Neutral point is white).increases. (Neutral point is white).

1% males & 0.02% of females are protanopes, approximately.1% males & 0.02% of females are protanopes, approximately.


Deuteranopia Green(chloralabe) is replaced with red (erythrolabe).Green(chloralabe) is replaced with red (erythrolabe).

Confuse red and green.Confuse red and green.

Blue perceived below 498nm and yellow above it.Blue perceived below 498nm and yellow above it.

Neutral point of deuteranope is higher than protanope. Neutral point of deuteranope is higher than protanope. ( 498 vs. 492nm) ( 498 vs. 492nm)


Tritanopia Tritanopia Blue(cyanolabe) may be absent.Blue(cyanolabe) may be absent.

Sensitive to yellow and blues.Sensitive to yellow and blues.

Neutral point occurs at 570nm.Neutral point occurs at 570nm.

Very rare condition (0.002% of males and Very rare condition (0.002% of males and 0.001% of females.) 0.001% of females.)


Problems in daily lifeProblems in daily life

Many works depends on color discrimination.Many works depends on color discrimination.

Defects may affect an individual ‘s ability.Defects may affect an individual ‘s ability.

Color defects could be costly even disastrous.Color defects could be costly even disastrous.


Tests for color visionTests for color vision Many tests are currently used to detect certain color vision defects.Many tests are currently used to detect certain color vision defects.

All vary in popularity and reliability.All vary in popularity and reliability.

Most common tests areMost common tests are

Ishihara pseudo- isochromatic plates.Ishihara pseudo- isochromatic plates.

American Optical plates. (HRR test)American Optical plates. (HRR test)

The City University testThe City University test

The Farnsworth Munsell D15 test.The Farnsworth Munsell D15 test.

The Farnsworth- Munsell 100 hue test (FM 100 hue)The Farnsworth- Munsell 100 hue test (FM 100 hue)

Color Arrangement Tests Color Arrangement Tests

The Anomaloscope Test The Anomaloscope Test


Ishihara pseudo- isochromatic plates.Ishihara pseudo- isochromatic plates.


Ishihara pseudo- isochromatic plates.Ishihara pseudo- isochromatic plates. Widely used and efficient test for red-green color deficiency.Widely used and efficient test for red-green color deficiency.

Contains 38 plates (25 numerals and 13 plates pathways). Contains 38 plates (25 numerals and 13 plates pathways).

Of the 25 plates, Of the 25 plates,

one is for demonstration of the visual task, one is for demonstration of the visual task,

20 are for red-green screening, and 20 are for red-green screening, and

four are for classification of red and green cone deficiencies. four are for classification of red and green cone deficiencies.

three plates intended for use with nonverbal subjects. three plates intended for use with nonverbal subjects.

Dichromate and anomalous trichromats fail to distinguish the number. Dichromate and anomalous trichromats fail to distinguish the number.

slight protanopes and deutranopes read some plates correctly.slight protanopes and deutranopes read some plates correctly.


American Optical plates. (HRR test)American Optical plates. (HRR test) To identify protan, deutan and tritan defects, and to grade their severity. To identify protan, deutan and tritan defects, and to grade their severity.

Consists of 24 plates containing symbols and employs neutral colours.Consists of 24 plates containing symbols and employs neutral colours.

4 introductory plates, 4 introductory plates,

6 plates for colour vision screening, and 6 plates for colour vision screening, and

14 plates for grading the severity of protan,deutan and tritan defects. 14 plates for grading the severity of protan,deutan and tritan defects.

Best for the detection of moderate or severe tritan defects.Best for the detection of moderate or severe tritan defects.

Not possible to distinguish dichromats and severe anomalous trichromats.Not possible to distinguish dichromats and severe anomalous trichromats.

HRR plates for estimating the severity of colour deficiency and for tritan HRR plates for estimating the severity of colour deficiency and for tritan

screening. screening.


The City University testThe City University test

Derived from the D-15 panel. Derived from the D-15 panel.

Contains ten plates(Each plate displays a central colour & 4 peripheral colours. Contains ten plates(Each plate displays a central colour & 4 peripheral colours.

Observer must select the peripheral colour which looks most similar to the central Observer must select the peripheral colour which looks most similar to the central

colour. colour.

3 colours are typical iso-chromatic confusions for protan,deutan and tritan 3 colours are typical iso-chromatic confusions for protan,deutan and tritan

deficiency. deficiency.

44thth colour is an adjacent colour in the D-15 sequence and is the normal. colour is an adjacent colour in the D-15 sequence and is the normal.

Classification of congenital protan and deutan defects is imprecise due to the Classification of congenital protan and deutan defects is imprecise due to the

limited choice of confusion color.limited choice of confusion color.

Grading test not a screening test.Grading test not a screening test.

Used to identify the severity of the colour defect.Used to identify the severity of the colour defect.


Farnsworth Munsell D15 testFarnsworth Munsell D15 test


Farnsworth Munsell D15 test.Farnsworth Munsell D15 test.

Consists of 15 loose caps and one fixed cap (the reference cap) in one box. Consists of 15 loose caps and one fixed cap (the reference cap) in one box.

Each cap hue is chosen so that adjacent caps have approximately equal hue Each cap hue is chosen so that adjacent caps have approximately equal hue differences. differences.

If caps are arranged in order out of their box forms a hue circle to detect errors If caps are arranged in order out of their box forms a hue circle to detect errors Standard D15 test divides people into two groups. Standard D15 test divides people into two groups.

people with normal colour vision and slight colour deficiency people with normal colour vision and slight colour deficiency

people with moderate and severe colour vision deficiency. people with moderate and severe colour vision deficiency.

Typical results obtain in congenitalprotan,deutan,andtritan colour deficiency.Typical results obtain in congenitalprotan,deutan,andtritan colour deficiency.

Not designed for screening. Not designed for screening.

It separates It separates sufficiently affected deutans from protans. sufficiently affected deutans from protans.

sufficiently affected deutans and moderate protans.sufficiently affected deutans and moderate protans.


The Farnsworth-Munsell 100 hue The Farnsworth-Munsell 100 hue test (F-M 100 hue)test (F-M 100 hue)

To detect all types of abnormality from the mildest red-green defect to total achromatopsia. To detect all types of abnormality from the mildest red-green defect to total achromatopsia.

It separates persons with normal colour vision from various color discrimination and It separates persons with normal colour vision from various color discrimination and

Measures the axes or zones of colour confusion in those with defective colour vision. Measures the axes or zones of colour confusion in those with defective colour vision.

Consists of 85 caps which form a perfect hue circle of the visual spectrum. Consists of 85 caps which form a perfect hue circle of the visual spectrum.

The hue circle is divided into four parts for the testing.The hue circle is divided into four parts for the testing.

Each has an additional fixed or pilot cap at either end of the box and 22 or 21 loose caps.Each has an additional fixed or pilot cap at either end of the box and 22 or 21 loose caps.

4boxes render it impossible to confuse reds with greens, or blues with yellows. 4boxes render it impossible to confuse reds with greens, or blues with yellows.

Most comprehensive type tests, giving both differential diagnosis and progression of the Most comprehensive type tests, giving both differential diagnosis and progression of the disease. disease.

Used to screen for any type of colour vision loss.Used to screen for any type of colour vision loss.

Takes long time to complete for an acquired loss patientsTakes long time to complete for an acquired loss patients


Anomaloscope TestAnomaloscope TestNagal anamaloscopeNagal anamaloscope Commonly used in the diagnosis of red-green deficiencies. Commonly used in the diagnosis of red-green deficiencies.

Assesses the observer’s ability to make a specific colour match. Assesses the observer’s ability to make a specific colour match.

Patient looks into the anomaloscope via eyepiece to view a bipartite colour field. Patient looks into the anomaloscope via eyepiece to view a bipartite colour field.

A mixture field composed of red and green wavelengths is presented in the top A mixture field composed of red and green wavelengths is presented in the top half of the display, the bottom half of the test field is yellow. half of the display, the bottom half of the test field is yellow.

Patient adjusts the mixture field to match the colour of the test field. Patient adjusts the mixture field to match the colour of the test field.

Distinguish between dichromatic and anomalous trichromatic vision by measuring Distinguish between dichromatic and anomalous trichromatic vision by measuring the balance of red and green wavelengths in the mixture field. the balance of red and green wavelengths in the mixture field.


Who may be affected?Who may be affected?

Corneal ulcerCorneal ulcer

Diplopia.Diplopia.

Eye haemorrhages.Eye haemorrhages.

MyopiaMyopia

OphthalmoplegiaOphthalmoplegia

Optic atrophies.Optic atrophies.

Optic neuritis.Optic neuritis.

Retinal detachment.Retinal detachment.

Diabetic retinopathy.Diabetic retinopathy.

Retinitis pigmentosaRetinitis pigmentosa


Enhancing the color defect performancesEnhancing the color defect performances Colored filtersColored filters

absorb the selected wavelengths absorb the selected wavelengths

help to differentiate stimuli based on their relative brightness. help to differentiate stimuli based on their relative brightness.

For example, For example, A A redred object viewed through a green filter or a green object viewed object viewed through a green filter or a green object viewed

through a red filter will appear much darker. through a red filter will appear much darker.

X-chromeX-chrome lens wears on one eye that absorbs shorter wavelengths and lens wears on one eye that absorbs shorter wavelengths and passes longer ones. passes longer ones.

Dichromat's ability to distinguish red from green can be enhanced. Dichromat's ability to distinguish red from green can be enhanced.

While such monocular comparisons may be useful in specific While such monocular comparisons may be useful in specific applications, the user remains a dichromatic and is unlikely to find the applications, the user remains a dichromatic and is unlikely to find the approach practical for everyday approach practical for everyday useuse..


TThahanknk Y Yoouu

aravind eye care system a r a v i n d e y e h o s p i t a l & postgraduate institute of...

Documents

r e s y s t e

n d e y e c

n d e y e h o s p i

red cones

individual s ability

green cones

blue cones

color defects