Colour vision
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Colour vision. P.S.Selvakumar Faculty Aravind School of Optometry. 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.

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Colour vision

Colour vision



Aravind School of Optometry

What is colour vision

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.

Light sensitive receptors

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.

Types of cones

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.

Color vision defects deficiencies

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.

Types of color vision defects

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.



  • 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.



  • 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.



  • 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)



  • 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.)

Problems in daily life

Problems in daily life

  • Many works depends on color discrimination.

  • Defects may affect an individual ‘s ability.

  • Color defects could be costly even disastrous.

Tests for color vision

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

Ishihara pseudo isochromatic plates

Ishihara pseudo- isochromatic plates.

Ishihara pseudo isochromatic plates1

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.

American optical plates hrr test

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.

The city university test

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.

Farnsworth munsell d15 test

Farnsworth Munsell D15 test

Farnsworth munsell d15 test1

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.

The farnsworth munsell 100 hue test f m 100 hue

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

Anomaloscope test

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.

Who may be affected

Corneal ulcer


Eye haemorrhages.



Optic atrophies.

Optic neuritis.

Retinal detachment.

Diabetic retinopathy.

Retinitis pigmentosa

Who may be affected?

Enhancing the color defect performances

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.

Colour vision

Thank You

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