Define Ishihara's Charts - Colour Blindness
Colour blindness is often assessed using Ishihara's charts. If ever you visited an eye specialist, you too must have seen this chart. In this, the numbers are inscribed amongst different dotted coloured background.
The degree of dotted coloured background is enhanced progressively thereby making it more and more difficult to discern numbers. Trichromates i.e. normal individuals can distinguish these numbers easily, while colour blind individuals cannot see or they recognize a wrong number.