The document discusses color and color vision, detailing the properties of color, theories of color perception, and types of color vision defects, including inherited and acquired conditions. It describes various tests for color vision and outlines the importance of color coding in occupational safety, specifying meanings assigned to colors by OSHA. Key colors and their safety implications are explained, such as red for danger, yellow for caution, and blue for out-of-service equipment.

1. Colour and eye
Kakoli Mahanta
Department of Optometry
School of Allied Health sciences
Sharda University

2. Colour and Colour vision
• Colour: The property possessed by an object of
producing different sensations on the eye as a
result of the way it reflects or emits light.
• Colour vision: It is the ability to distinguish
among various wavelengths of light waves and to
perceive the differences in hue. The normal
human eye can discriminate among hundreds of
such bands of wavelengths as they are received by
the colour-sensing cells (cones) of the retina.

3. Two major theories of colour perception
• Trichromatic theory : Normal color vision person
match any color by a suitable mixture of three primary
colors. By Thomas young, Helmholtz, Maxwell.
• Opponent color theory: Four primaries. Red,
Green, Yellow and Blue.
• Three mechanisms : red green, yellow blue and white
black .
• Response in one direction for warm colors
(red ,yellow and white) and response in opposite
direction for cold colors ( green, blue and black).

4. Colour vision defects
• Color vision defects can be either inherited or acquired color
vision defects.
• Inherited- are non pathological, incurable conditions and do
not change overtime. The most common are the red green
defects which are inherited as an x linked recessive trait.
• Acquired- usually accompany another condition such as
disease or trauma or due to side effects of certain drugs,
medication or exposure to chemical toxins. Acquired color
vision defects may also be congenital or inherited but the
color deficiency is secondary to cause or condition. Acquired
defects are usually of blue yellow type.

5. Types of defects
• Anomalous trichromatism: uses 3 primary colour but requires a
different intensity of each primary compared with normal
trichromat.
▫ Protanomalous(Red weak)
▫ Duteranomalous (Green weak)
▫ Tritanomalous (Blue weak)
• Dichromatism: uses only two primary colors to match any
perceived color.
▫ Protanopia lacks red absorbing pigment known as erythrolabe.
▫ Deuteranopia lacks a green absorbing pigment known as chlorolabe.
▫ Tritanopia lacks a blue absorbing pigment known as cyanolabe.
• Monochromatism (Achromatopsia): an extremely rare condition
occurring only one in one million people. A monochromat only uses
one primary color to match any color in the spectrum. It occurs in 2
forms, both of which are present at birth.
▫ Rod Monochromatism
▫ Cone monochromatism

6. Colour vision test
• Pseudo Isochromatic Plates - These plates are most commonly
used for color vision testing. They are easily & rapidly administered
most are designed to screen for presence of red-green inherited color
vision defects. Ex: Ishihara chart, Divorine Test, American Optical
Company plates.
• Arrangement Tests- These tests are most useful for both inherited
& acquired color defects. The result not only permits diagnosis of the
type of defect but also helps to asses the severity of defect. Ex:
Fransworth-munsel D-15 Test, Fransworth 100 Hue Test
• Anomaloscopes- These are generally accepted as the most accurate
test in diagnosis of color vision defects. Ex: Nagel Anomaloscope

8. Colour coding
• Colour coding is a visual reminder system to warn,
inform and guide employees.
• Occupational Safety and Health Administration (OSHA)
assigns specific meanings to certain colours.
• Hence colours can be a warning of a particular hazard or
give information or directions.
• Colour coding is considered highly desirable. The main
intent, however, is not to demand it in shops and
laboratories, but to recognize a standard colour code
wherever colour coding is used. Be aware of your specific
work area and the colour coding system used there.

9. These colours usually indicate the following
• Red – either(1) danger, (2) stop or (3) presence of fire
protection equipment.
• Orange – marks the dangerous parts of machines or
energized equipment which may cut, crush, shock or
injure employees. Orange emphasizes these hazards
when the guards or enclosures around them are open.
• Yellow – warns of physical hazards and means caution.
A striped or checkered pattern of yellow and black may
be used to help attract attention.

10. • Blue – denotes caution and its use is restricted to
marking out-of-service equipment which should not be
used.
• Green – indicates either the location of safety
equipment such as first aid materials or conveys safety
information.
• Purple – used for radiation hazards. It may contain a
combination of purple and yellow.
• Black & White – or a combination of the two are used
to designate traffic and housekeeping markings.
Stripes, checkers or other variations are often used.