What Causes Dogs to Have Two Different Coloured Eyes?

Most dogs typically have eyes in shades of brown, from deep chocolate to amber. However, some have eyes of strikingly different colours — a condition known as heterochromia iridis, where one eye may be blue and the other brown or amber.

Heterochromia iridis occurs due to differences in melanin pigment between the two irises. Melanin is responsible for eye colour, just as it is for coat colour. Puppies are usually born with blue eyes until melanin production increases over the first weeks of life, changing eye colour in most dogs.

If you've seen Siberian husky puppies or Australian shepherd puppies with one eye that's blue and the other brown, you're witnessing one of the canine world's most beautiful genetic quirks.

How Does Eye Colour Develop in Dogs?

Eye colour in dogs is determined by the amount and distribution of melanin in the iris. When melanin production is high, the eyes appear darker brown; when melanin is scarce or absent, the eyes appear blue. This is why most newborn puppies start life with blue eyes, which gradually change as melanin develops.

Variations in pigment can lead to heterochromia, where each eye has a different colour due to unequal melanin levels. This trait is genetically inherited but can also arise from genetic mosaicism or chimerism — where different genes affect pigmentation during development.

Why Do Some Dogs Have Heterochromia?

Heterochromia is primarily a genetic trait. For it to express, a dog must inherit specific combinations of genes affecting melanin. This is why it occurs more frequently in breeds like Siberian Huskies (Siberian husky puppies) and Australian Shepherds (Australian shepherd puppies), which carry gene variants influencing eye and coat pigment distribution.

Heterochromia can be of three types:

• Complete heterochromia iridis: Each eye is fully different in colour.
• Sectoral heterochromia: Part of one eye differs in colour, creating a 'slice' effect.
• Central heterochromia: A ring or pattern of different colour radiates from the pupil.

Genetic Factors and Responsible Breeding

The genes associated with heterochromia often relate to coat patterns such as merle or piebald. For instance, the blue merle gene causes unique coat colourations and can heighten the prevalence of heterochromia. However, breeding two blue merle dogs carries a risk of producing double merle offspring, which may suffer from sensory problems like deafness or vision issues.

Because of these risks, responsible breeders avoid mating two merle-patterned dogs and test for genetics to minimise health problems while preserving the breed's natural traits. This approach helps to ensure puppies with heterochromia also have robust health and wellbeing.

Heterochromia and Dog Health

In most cases, heterochromia is purely cosmetic and does not affect a dog's vision or health. Dogs with two different coloured eyes see perfectly well. However, if a dog's eye colour changes suddenly or if accompanied by symptoms like inflammation or discharge, it may signal an injury or illness, requiring prompt veterinary attention.

As a pet owner, understanding this condition helps in recognising when to enjoy a stunning feature or when to seek help for your dog’s eye health.

Summary and What to Remember

• Most dogs have brown eyes; blue or green eyes are less common.
• Heterochromia iridis means each eye has a different colour, caused by genetics and pigment differences.
• It is commonly seen in breeds like Siberian Huskies and Australian Shepherds.
• Responsible breeding avoids risky gene combinations like double merle to prevent health issues.
• Heterochromia usually does not impact vision but sudden changes or symptoms need vet check-ups.

Heterochromia iridis is a captivating glimpse into canine genetics and natural variation, reminding us of the wonderful complexity behind every dog's unique appearance.