Colour-Blindness: some salient things you should know

Being "colour blind" has been incorrectly described (commonly) as seeing stuff in black & white like in the 80's photographs, but this understanding is mostly wrong.

Colour blindness is a medical condition characterized by the inability of the eye to recognize/acknowledge one or more colours. It affects more males (8%) than females (0.4%) due to the fact that it is an inherited sex-linked recessive character. It is worthy to note that total colour blindness (in this case, seeing stuff in plain black & white) is extremely rare. However, asides from hereditary, colour blindness can be acquired as a result of effects from external factors such as injury to the eye or even ocular diseases.

CAUSES OF ACQUIRED COLOUR-BLINDNESS

1.) Chronic Diseases

Colour-blindness has been associated with quite a number of chronic diseases, some of which includes:

• Glaucoma

• Parkinson's disease

• Alzheimer's disease

• Leukaemia

• Diabetes

• Liver diseases etc.

2.) Excessive Use of Drugs/Medications

Too much of anything in life usually comes with side effects. Some drugs of which their excessive usage can cause or lead to onset of colour-blindness includes:

• Antibiotics.

• Antihypertensive drugs.

• Antituberculiosis drugs etc.

3.) Exposure to Toxins and Certain Substances

Some substances such as Carbon monoxide, Carbon disulphide or chemicals high in Lead concentration can be very dangerous to the eye. It is advised you stay away from them as much as possible, or use adequate protective equipments when handling them.

4.) Aging

The aging process is inevitable; as we grow older, our body's organs and systems tend to lose their efficiency due to the diminishing number of total cells in the body (and to a large extent, the effect of free radicals generated by oxidative stress in cells).

Colour-blindness often occurs after 60 years of age as a result of various changes in the eye.

5.) Trauma

6.) Alcoholism

CLASSIFICATION OF COLOUR-BLINDNESS

There are three (3) main classes of colour blindness:

• Monochromatism

• Dichromatism

• Trichromatism

1.) Monochromatism

This is also called achromatopia. It is distinguished by the total inability to perceive colour; and thus it is commonly called Total colour blindness. Monochromatism is extremely rare (keyword: extremely).

Monochromats — persons with monochromatism — see only in black, white and various shades of grey because the retina is completely insensitive to colour. It is subdivided into 2 types: Rod monochromatism and Cone monochromatism.

2.) Dichromatism

Dichromatism is the condition of colour-blindness whereby the person is able to perceive only two colours. Persons who suffer from Dichromatism are called Dichromats; they match the entire colour spectrum by two primary colours due to the defect of the receptor for the third primary colour.

Dichromatism is subdivided into 3 types:

• Protanopia — There is defect in the receptor of the first primary colour - Red; thus red colour cannot be perceived. Blue & Green are used to match the colours and Red is confused with Green. Patients who have this specific type of Dichromatism are called Protanopes.

• Deuteranopia — There is defect in the receptor for Green. Thus Green colour cannot be perceived. Blue & Red are used to match the colours. Patients who have this specific type of Dichromatism are called Deuteranopes.

• Tritanopia — There is defect in the receptor of the third primary colour - Blue. Patients who have this specific type of Dichromatism — Tritanopes — use Red & Green to match colours; they cannot perceived blue colour.

3.) Trichromatism

Trichromatism is the colour-blindness in which the intensity of one of the primary colours is not fully perceived or appreciated. However, patients — Trichromats — are able to perceive all the three colours.

Trichromatism is subdivided into 3 types:

• Protanomaly — Perception for red colour is weak; thus to really perceive/appreciate red, the person requires more intensity of red than a normal person (think of it as increasing the saturation, like in photo-editing)

• Deuteranomaly — In this type of Trichromatism, perception for Green colour is weak/low.

• Tritanomaly — Perception for blue colour is weak/low.

COLOUR-BLINDNESS TESTS

There are three (3) methods/tests for colour-blindness — Ishihara Colour Charts, Edridge-Green Lantern and Holmgren Coloured Wool. Detailed description of these tests can be found online in Wikipedia and a host of reputable medical journals.