The Ishihara test is the most common, non-invasive, and rapid screening tool used to detect red-green color blindness. It consists of a series of plates (circles) filled with colored dots, forming numbers or shapes that individuals with normal, deficient, or no color vision perceive differently. 

Key Details About the Ishihara Test

• Purpose: Specifically designed to detect congenital red-green color deficiencies, though it can also identify acquired color vision defects.
• Structure: It typically uses 8 to 34 "plates" (pseudoisochromatic plates). Each plate contains dots of varying colors and sizes, making numbers or, in some versions for children, lines to trace.
• Methodology: The viewer sits in normal lighting and identifies the number or pattern on each plate within 3 seconds.
• Interpretation:
• Normal Color Vision: Reads one number.
• Red-Green Deficiency: Reads a different number or cannot see a number at all.
• Variations: The test includes transformation plates (different numbers for normal/deficiency), vanishing plates (hidden for deficient eyes), and hidden digit plates.