COLOUR VISION

 

ANDY ASARE ANTWI

Colour vision, an integral part of visual perception and the visual system, is the ability to discriminate between different wavelengths of light regardless of the intensity of light. The faculty of being able to appreciate colour is absolutely necessary for our daily activities. Individuals who lack this faculty, either partially or completely, experience a wide range of difficulty. The colours most commonly associated with nature, including the beautiful blue colour of the ocean, and the glowing and captivating colourful horizon during sunrise and twilight, give immense pleasure to our eyes. 

Colour vision is possible due to the cone photoreceptors of the retina. These cones have light-sensitive pigments useful in colour perception and are more concentrated in the macula of the retina. For a developed, healthy and functioning human retina, there is trichromatic colour vision due to the three kinds of cone photoreceptors namely: short-wavelength cones, medium-wavelength cones and longwavelength cones. Each cone is sensitive to visible wavelengths of light that correspond to blue light, green light and red light. Traditionally, disorders of colour vision are classified into congenital and acquired defects. Congenital colour vision defect may result from alterations in the gene coding for the cone photopigment or absence of one or more photopigments and this defect is present from birth. The most common defects are: Protan defects, where there is L-cone defect (Red Light), Deutan defects, where there is M-cone defect (Green light) and Tritan defects, where there is S-cone defect (Blue light). These defects are milder than Achromatopsia where there is complete loss of colour vision. 

Several research studies show that colour vision deficiency affects more males than females. Also, most people with colour deficiency can actually see colours. An individual with red-green colour blindness means the person has difficulty in differentiating between these colours. In most cases, genetics cause colour deficiency and it is usually an inherited condition caused by a common X-linked recessive gene. Moreover, macular degeneration, diabetes, glaucoma, sickle cell anaemia and some pharmacological agents can cause colour deficits. Defects in colour vision can be frustrating and may limit participation in certain activities. However, an intact colour perception is thought to be critical to allow an ideal environment.