Why Do Kittens Have Blue Eyes at Birth? The Science Behind Their Eye Color Change

Introduction

Cats are born with blue eyes, yet many cats have yellow, green, orange, brown, or hazel eyes as adults. This article will provide an overview of why kittens start with blue eyes and how their eye color changes over time. We’ll explore the biology behind eye color in cats, look at the role of melanin and genetics, discuss which breeds are more likely to retain blue eyes from kittenhood into adulthood, and address some common myths about blue eyes in cats.

To begin, we’ll discuss the developmental biology that causes kittens to be born with blue eyes, then we’ll cover the melanin production process that leads to permanent eye color later in life. Next, we’ll examine how a cat’s genotype influences their final eye color. We’ll also touch on any environmental factors that can impact eye color. Finally, we’ll wrap up by busting some myths and summarizing the key reasons why cats start out with blue eyes.

The Biology of Eye Color

The iris is the colored part of the eye located around the pupil. It contains pigment cells called melanocytes that produce melanin, which gives the iris its color. The amount and type of melanin produced determines eye color.

Newborn babies have very little melanin in their irises, which is why most Caucasian babies are born with blue eyes. Over the first few years of life, melanin production ramps up, leading to darker eye colors. The melanocytes don’t start actively producing melanin until several months after birth (Mackey, 2022).

The lack of melanin in newborns leaves the iris transparent, which reveals the underlying blue color caused by collagen fibers in the stroma. Increased melanin production leads to deposition of melanin granules in the iris, gradually reducing the transparency and blue appearance of the newborn eye.

The two main types of melanin are eumelanin which produces brown/black pigment, and pheomelanin which produces red/yellow pigment. The specific mix of eumelanin and pheomelanin produced determines the final eye color (MedlinePlus, 2022).

Kittens Are Born With Blue Eyes

Newborn kittens are born with blue eyes. This is because kittens are born with very little melanin in their irises, causing the eyes to appear blue in color. Melanin is the pigment that determines eye color in both animals and humans. Lack of melanin causes the light entering the eye to scatter, giving the eyes a blue appearance.

The tapetum lucidum, a light-reflecting layer behind the retina which helps animals see in dim light, also contributes to the blue eye color in newborn kittens. The tapetum lucidum causes eyes to glow blue when light shines into them. Kittens eyes will typically remain blue for the first week or two of life.

Some sources note that very young kittens may occasionally have darker eyes shortly after birth, but these will switch to blue within a day or two. The initial dark color likely occurs due to exposure to maternal hormones in the womb or birth fluids during delivery. But kittens are born without the ability to produce melanin on their own, so their eyes will quickly become blue.

According to http://www.kittenlady.org/age, kittens with blue eyes are under 7 weeks of age. As they grow older and begin producing melanin, their eye color will start to change. The blue eye color is a reliable indicator that a kitten is newly born.

Melanin Production Increases Over Time

As kittens mature, the amount of melanin in their eyes increases, which leads to a change in eye color. Melanin is the pigment that gives color to a cat’s fur, skin and eyes. When kittens are born, they have a very low level of melanin in their eyes, which is why their eyes initially appear blue.

Around 2-3 weeks of age, melanocytes which are cells that produce melanin, start to migrate into the iris of a kitten’s eyes. Over the next several weeks, these melanocytes start ramping up melanin production. As the amount of melanin increases in the iris, the kitten’s eye color starts to change and intensify.

By around 4-8 weeks of age, enough melanin has been produced to fully pigment the iris and the final, adult eye color emerges. So while kittens start out with blue eyes due to low melanin, their eye color transforms as melanocytes stimulate melanin production during maturation. The resulting eye color depends on genetics and can range from brilliant copper, deep gold, vibrant green and more.

Final Eye Color Depends on Genetics

A kitten’s final eye color is determined by the genes inherited from its parents. Cats have two main genes that influence eye color: the B gene and the D gene. The B gene codes for chocolate and cinnamon coat colors, while the D gene controls how dense the melanin pigment is in the iris.

There are two alleles (variants) for each of these genes: B and b, as well as D and d. The genotype bb produces a non-chocolate/cinnamon coat, while BB or Bb allows for chocolate/cinnamon coats. Similarly, dd results in little to no melanin and a blue eye color, while DD produces very dark melanin and amber/green/yellow eyes. A Dd genotype allows for an intermediate eye color like green.

Kittens inherit one allele from each parent for the B and D genes. The combination of alleles received determines the eye color. For example, a kitten that inherits dd will have blue eyes regardless of coat color. But a BB or Bb, Dd kitten will have green eyes if it has a chocolate/cinnamon coat. Understanding the parents’ genotypes can help predict kittens’ final eye colors.

In summary, kittens start with blue eyes due to low melanin levels. Their final eye color emerges over time based on the specific alleles coding for melanin production that are inherited from their parents.

Some Cats Retain Blue Eyes

While most kittens are born with blue eyes that change color as they mature, some cat breeds are more likely to retain blue eyes into adulthood. This is due to specific genes that inhibit the production of melanin and result in less pigmentation in the iris.

Breeds such as the Siamese, Birman, Ragdoll, Snowshoe, and Himalayan are known for their striking blue eyes. The level of melanin production is influenced by genetics, with variations in specific genes linked to blue eye color.

For example, the Birman breed has a gene that causes low levels of pigment in the fur and eyes. The Siamese lacks the gene for complete melanin production, resulting in the heat-sensitive albinism that gives the breed its signature light coat and blue eyes.

While genetics play a key role, even within breeds that tend to have blue eyes, eye color can vary based on family lines and purebred versus mixed ancestry. Proper breeding is needed to retain the blue eye trait across generations.

Environmental Factors May Influence Eye Color

While genetics play the biggest role, some environmental factors may also influence eye color in cats. The key is how these factors impact melanin production in the iris. Melanin is the pigment that gives eyes their color.

For example, nutrition can affect melanin levels. Kittens who are malnourished or deficient in certain nutrients like taurine may produce less melanin. This can result in lighter eye colors like blue. Ensuring proper nutrition supports healthy melanin levels and typical eye pigmentation (1).

Light exposure is another factor. Cats with more sun exposure tend to develop darker eye colors, while indoor cats usually retain lighter blue eyes. Sunlight stimulates increased melanin production. Limited light exposure does the opposite, inhibiting melanin in the iris (2).

While subtle changes are possible, most experts agree genetics are the primary determinant of feline eye color. But nutrition, light exposure, and other environmental influences can play a secondary role in melanin and pigment levels.

(1) https://basepaws.com/cat-insider/cat-eye-colors-unveiling-the-mysteries-behind-your-felines-gorgeous-eyes

(2) https://blog.catbandit.com/can-cats-eyes-change-colour/

Eye Color Isn’t Linked to Vision

A common myth is that eye color is linked to a cat’s vision and ability to see well. However, research shows that a cat’s eye color has no effect on its vision or ability to see at night.

According to veterinary experts, a cat’s vision and visual acuity is determined by the anatomy and health of its eyes, not simply eye color. For example, the shape of the eye, density of retinal receptors, size of the pupil opening, and health of the optic nerve play a much greater role.

Additionally, a Catster article notes that cats have a reflective membrane behind the retina called the tapetum lucidum that aids night vision. This membrane reflects light back through the retina, allowing the photoreceptors a second chance to capture photons and form an image. The tapetum lucidum gives cats excellent night vision, regardless of their eye color.

So while eye colors in cats can vary greatly, from brilliant blues to golden hues, the hue itself does not affect visual acuity or ability to see in low light. Vision is much more complex than just one genetic trait. As long as your cat has healthy eyes, they will have excellent vision capabilities.

Myths About Blue Eyes in Cats

There are a few common myths and misconceptions about cats with blue eyes that are important to address. One myth is that all blue-eyed cats are deaf. While blue-eyed cats do have a higher risk of deafness, especially if they have a white coat, not all blue-eyed cats are deaf. Deafness can occur in cats of any eye color.

Another myth is that as a kitten ages, its blue eyes will change to another color. While many kittens are born with blue eyes that turn into another color, not all blue-eyed kittens will experience this change. Some cats will retain their blue eye color into adulthood. The final eye color is determined by genetics.

There is also a myth that cats with blue eyes have vision problems or poorer eyesight. A cat’s eye color is not linked to their vision quality or visual acuity. Blue-eyed cats see just as well as cats with other eye colors. The only association between blue eyes and vision is the previously mentioned potential for deafness.

It’s important for cat owners to understand the facts around their pet’s eye color and not assume their cat has vision or hearing issues based on eye color alone. Proper veterinary screening is needed to diagnose deafness or other health conditions. With a basic grasp of the genetics around eye color, cat owners can better understand their pet’s beautiful baby blues.

Conclusion

To summarize, the reason that kittens start out with blue eyes is because at birth their eyes are still developing and they do not yet produce enough melanin to turn the eyes another color. All kittens are born with blue eyes because they do not start producing melanin, the pigment that colors the iris, until around 6-8 weeks of age. As they mature, increased melanin changes their eye color to shades of green, yellow, orange or brown, depending on genetics. Some cats maintain blue eyes throughout adulthood, but eye color is not linked to vision. While myths persist about blue eyes indicating deafness or other health issues, this is not true in the majority of cases. In the end, kittens start out with blue eyes simply because they have not yet developed the pigmentation that leads to their permanent eye color.

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