CHAPTER ONE INTRODUCTION Colour blindness can be simply defined as the inability to distinguish one or more of the three colours red, green and blue. The ability to see colours exists in only a few vertelerntes including among others man and the other privates, fish, amphibians, sone reptiles and same birds, and in bees and butterflies. In the retina- the light sensitive layer of tissue that lines the back and sides of the eyeball, there are in human beings three types of cones, the visual cells that function in the perception of colour. One type absorbs high best in wavelengths of blue – violet and another in the wavelength of green. The third type is most sensitive to wavelength of yellow but is also sensitive to red. Colour blind persons may be blind to one, two or all of the colours red, green and blue. (Blindness to red is called protanopia; to green denternopia and to blue tritanopia). Red blind persons are ordinarily able to distinguish between red and green white blue-blind persons cannot distinguish between blue and yellow, Green – blind persons are unable to see the green port of the spectrum. The Nomenclature of the varieties of colour blindness has become somewhat complicated and therefore something must be said about the theories of colour visions. Unfortunately more of the theories is yet completely established, but as a working hypothesis trichromatic holds the field, though recent work seems to show that at least six receptor work may be operative in the retina.