Colour vision
P.S.Selvakumar
Faculty
Aravind School of Optometry
ARAVIND EYE CARE SYSTEM
A RAV I N D E YE H O S PI TAL
& Postgraduate Institute of Ophthalmology
Madurai, India
What is colour vision?
 An ability to distinguish certain colors.
 Presents only in day light / bright light conditions &
absent at night / dark.
 Maximum sensitive color cones are considered.
 Normal person can match the 3 primary colors with all
spectral hues called, Trichromatic.
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Light sensitive receptors
 Rods (120 million)
Located in peripheral retina.
Responsible for night vision.
 Cones ( 7 million)
Responsible for color vision ,day vision and sharper vision.
Located around fovea region.
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Types of cones
 Red, Blue and Green
 74% red cones.
 16% blue cones.
 10% green cones.
 Color discrimination occurs through the integration of all
cones.
 Yellow perceives from red and green combination.
 White perceives from inputs of all cones.
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Color vision defects / deficiencies
 Due to absence / defects of cones.
 Unable to interpret the signals to brain.
 Classified as either hereditary or acquired.
 Affects about 8% of men & 0.5% women.
 Abnormal color matching and color confusions
may be result.
 Grass may appear in orange color.
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Types of color vision defects
 Trichromatic – all cones present – normal vision.
 Dichromatic – one cone completely absent
 Monochromatic – only one cone present.
 Achromatic – no functioning cones.
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Dichromacy
 Two cone receptors for matching with all spectral hues.
 Three types.
 Red and green defects
 Are sex-linked.
 Protanopes - lack of red receptors.
 Deutranopes – lack of green receptors.
 Blue and yellow confusion due to
 Tritanopes – lack of blue receptor
 CIE Chromaticity diagram useful to identify dichromats.
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Protanopia
 Red (erytholabe) is absent and replaced by green (chlorolabe).
 Protanopes confuses red and green.
 Blue become less saturated until 492nm,as wavelengths
increases. (Neutral point is white).
 1% males & 0.02% of females are protanopes, approximately.
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Deuteranopia
 Green(chloralabe) is replaced with red (erythrolabe).
 Confuse red and green.
 Blue perceived below 498nm and yellow above it.
 Neutral point of deuteranope is higher than protanope.
( 498 vs. 492nm)
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Tritanopia
 Blue(cyanolabe) may be absent.
 Sensitive to yellow and blues.
 Neutral point occurs at 570nm.
 Very rare condition (0.002% of males and
0.001% of females.)
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Problems in daily life
 Many works depends on color discrimination.
 Defects may affect an individual ‘s ability.
 Color defects could be costly even disastrous.
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Tests for color vision
 Many tests are currently used to detect certain color vision defects.
 All vary in popularity and reliability.
 Most common tests are
 Ishihara pseudo- isochromatic plates.
 American Optical plates. (HRR test)
 The City University test
 The Farnsworth Munsell D15 test.
 The Farnsworth- Munsell 100 hue test (FM 100 hue)
 Color Arrangement Tests
 The Anomaloscope Test
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Ishihara pseudo- isochromatic plates.
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Ishihara pseudo- isochromatic plates.
 Widely used and efficient test for red-green color deficiency.
 Contains 38 plates (25 numerals and 13 plates pathways).
 Of the 25 plates,

one is for demonstration of the visual task,

20 are for red-green screening, and

four are for classification of red and green cone deficiencies.

three plates intended for use with nonverbal subjects.
 Dichromate and anomalous trichromats fail to distinguish the number.
 slight protanopes and deutranopes read some plates correctly.
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American Optical plates. (HRR test)
 To identify protan, deutan and tritan defects, and to grade their severity.
 Consists of 24 plates containing symbols and employs neutral colours.

4 introductory plates,

6 plates for colour vision screening, and

14 plates for grading the severity of protan,deutan and tritan defects.
 Best for the detection of moderate or severe tritan defects.
 Not possible to distinguish dichromats and severe anomalous trichromats.
 HRR plates for estimating the severity of colour deficiency and for tritan
screening.
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The City University test
 Derived from the D-15 panel.
 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
colour.
 3 colours are typical iso-chromatic confusions for protan,deutan and tritan
deficiency.
 4th 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 limited
choice of confusion color.
 Grading test not a screening test.
 Used to identify the severity of the colour defect.
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Farnsworth Munsell D15 test
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Farnsworth Munsell D15 test.
 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
differences.
 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.

people with normal colour vision and slight colour deficiency

people with moderate and severe colour vision deficiency.
 Typical results obtain in congenitalprotan,deutan,andtritan colour deficiency.
 Not designed for screening.
 It separates

sufficiently affected deutans from protans.

sufficiently affected deutans and moderate protans.
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The Farnsworth-Munsell 100 hue
test (F-M 100 hue)
 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
 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.
 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.
 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
disease.
 Used to screen for any type of colour vision loss.
 Takes long time to complete for an acquired loss patients
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Anomaloscope Test
Nagal anamaloscope
 Commonly used in the diagnosis of red-green deficiencies.
 Assesses the observer’s ability to make a specific colour match.
 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
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.
 Distinguish between dichromatic and anomalous trichromatic vision by measuring
the balance of red and green wavelengths in the mixture field.
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Who may be affected?
 Corneal ulcer
 Optic atrophies.
 Diplopia.
 Optic neuritis.
 Eye haemorrhages.
 Retinal detachment.
 Myopia
 Diabetic retinopathy.
 Ophthalmoplegia
 Retinitis pigmentosa
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Enhancing the color defect performances
 Colored filters
 absorb the selected wavelengths
 help to differentiate stimuli based on their relative brightness.
 For example,
 A red object viewed through a green filter or a green object viewed
through a red filter will appear much darker.
 X-chrome lens wears on one eye that absorbs shorter wavelengths and
passes longer ones.
 Dichromat's ability to distinguish red from green can be enhanced.
 While such monocular comparisons may be useful in specific
applications, the user remains a dichromatic and is unlikely to find the
approach practical for everyday use.
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Thank You
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