Colour Deficiency (Colour Blindness)

What It Is 

Colour deficiency occurs when the ability to distinguish certain colours and shades is reduced or altered. 
While often called “colour blindness,” complete colour blindness — called achromatopsia — is extremely rare. 
Most people with colour deficiency can still see colours, but perceive them differently. The condition affects roughly 1 in 10 males and is much less common in females. 

 

Who It Affects / Risk Factors 

• Typically inherited, passed from mother to son 
• Can also result from eye disease, optic nerve damage, or certain medications 
• More common in males than females 
• May appear in childhood, often unnoticed without testing 

 

Types of Colour Deficiency 

🔴🟢 Red–Green Deficiency 

The most common type, affecting the ability to tell apart certain shades of: 

Reds, browns, pinks, and oranges 

Greens and blues 

🔵💛 Blue–Yellow Deficiency 

Much rarer, often caused by optic nerve or retinal damage, and affects the ability to tell apart: 

Blues and yellows 

⚫⚪ Complete Colour Blindness (Achromatopsia) 

Extremely rare. People see in shades of black, white, and grey only. 

 

How It’s Diagnosed 

A comprehensive eye exam with your optometrist includes simple colour vision testing — often using Ishihara plates, which show coloured patterns or numbers. 
People with colour deficiency may see a different number or no pattern at all. 
Testing is important because many children with colour deficiency don’t realize they see colours differently. 

 

When to See Your Optometrist 

• Every child should be tested for colour deficiency by age six. 
• Early detection helps support colour-coded learning in school. 
• Adults should be tested if they notice colour confusion or if their job requires accurate colour vision, such as pilots, electricians, firefighters, or police officers. 

 

Treatment & Management 

There is no known cure for colour deficiency, but optometrists can help manage it: 

Teach colour recognition techniques, like using position cues (e.g., traffic light order). 

Recommend special filters or lenses that may enhance colour distinction. 

Provide advice for adapting to school, work, or daily life. 

 

Related Topics 

[Retina & Optic Nerve Health] 

[Children’s Eye Exams] 

[Inherited Eye Conditions] 

 

Resources & Programs 

[Eye See…Eye Learn® – Free Eye Exams for Children] 

[OHIP Coverage for Eye Exams] 

[Teleoptometry Services] 

 
 

💙 Book an Eye Exam — Optometrists can identify colour deficiency early and provide guidance to support learning and everyday vision needs.