Introduction
The iris is the colored part of a cat’s eye surrounding the pupil. It controls how much light enters the eye by allowing the pupil to dilate and constrict. The iris color in cats can change over time due to various factors.
Iris color changes are a well-known phenomenon in cats, especially kittens. As a kitten develops into an adult cat, melanin pigment continues to be deposited in the iris, which can cause striking color changes in the first few months. But other factors throughout a cat’s life can also impact iris color.
In this article, we will examine the common causes of feline iris color change and what it means for your cat’s health and breed identification.
Causes
A cat’s iris, the colored part of the eye surrounding the pupil, can change colors for a variety of reasons. Some of the main causes include:
Genetics
Kittens are often born with blue eyes that can change to other colors as they mature. The final adult eye color is determined by genetics. For example, all white cats with blue eyes carry a gene that limits melanin production, keeping their eyes blue. Eye color in cats is linked to coat color due to the connection between melanin production and eye/coat pigmentation.
Breed
Certain cat breeds are known for their distinctive eye colors. Siamese cats usually have blue eyes. Persian cats often have brilliant copper or green eyes. The Tonkinese breed typically has aqua eyes. Eye color can be a defining characteristic for some breeds.
Age
Kittens are born with blue eyes that often change to their permanent adult colors between 6-8 weeks old as melanin production increases. However, some cats can experience pigment changes as they age, causing subtle shifts in eye color over time.
Diseases
Certain diseases that affect the eyes or body can influence eye color. For example, feline leukemia, feline immunodeficiency virus, and feline infectious peritonitis may cause eye color changes. Diabetes, hyperthyroidism, and other systemic diseases can also impact pigmentation.
Injuries
Trauma to the eyes can cause color changes. After injuries, the iris may lose pigmentation and appear lighter. Blood trapped in the eye after trauma can also change the eye color until it is reabsorbed.
Nuclear Sclerosis
A common age-related eye condition called nuclear sclerosis causes the lens to gradually harden. This can make the eyes appear cloudy or bluish-gray. However, nuclear sclerosis does not actually change the iris pigmentation itself.
Genetics
A cat’s eye color is primarily determined by genetics. The amount of melanin pigment in the iris determines eye color, with more melanin leading to darker eyes. Eye color is an inherited polygenic trait, meaning multiple genes are involved in controlling melanin production and distribution in the iris. The primary gene responsible for cat eye color is the coat color gene (TYR), which has different variations or alleles that code for specific pigments. The allele that codes for dense, black pigment is dominant and leads to darker eyes like green, hazel, or copper. Recessive alleles code for less or no melanin pigment and result in blue or yellow eyes.
Certain cat breeds are more prone to changing eye colors due to their genetics. Breeds like the Tonkinese, Russian Blue, and Siamese often experience color changes from blue to green or yellow to green as they age. This change happens because the kitten has inherited a form of incomplete dominant allele that allows limited melanin production early in life. As the cat matures and more melanin is produced, usually between 6-16 weeks, eye color transitions from lighter to darker shades.
While genetics are the primary determinant of feline eye color, other factors can also influence pigment distribution and lead to color variations over a cat’s lifetime.
Breeds
It is common for some cat breeds to experience iris color changes, particularly from blue to a yellow/green or copper color as they age. This is due to genetics and normal maturation. Some breeds known for eye color changes include:
- Siamese – Siamese cats are born with blue eyes that typically darken to a light blue or aqua shade by 10-12 weeks old.
- Ragdoll – Ragdoll kittens have blue eyes at birth that change to a green, greenish-blue, or blue-violet hue around 2-3 months old.
- Birman – Birmans are born with deep blue eyes that transform to sapphire blue around 16 weeks old.
- Tonkinese – Tonkinese cats have blue eyes as kittens that turn aquamarine or greenish-gold as adults.
- Russian Blue – Russian Blues usually have green or greenish-blue eyes, though some kittens are born with yellowish eyes that turn green with maturity.
- Balinese – Balinese cats have blue eyes as kittens that change to a vivid blue as adults.
For these breeds, iris color transformation is an expected part of development. However, any sudden changes in eye color can indicate health issues, so owners should monitor their cat’s eyes closely.
Age
A kitten’s eye color at birth is determined by genetics, but the final eye color doesn’t fully develop until the kitten matures. Newborn kittens can be born with blue eyes, but the melanin pigment in the iris develops as the kitten ages, changing the eye color.[1]
Most kittens’ eye color changes by the time they are three months old, but it can take up to six months for the eye color to fully develop. By six to eight weeks of age, kittens’ eyes begin changing from blue to their permanent adult color. The tapetum lucidum, a reflective layer of the eye that helps with night vision, isn’t fully formed until the kitten is around four months old.
As cats grow older, their eye color may gradually become more muted. An aging cat’s eyes can change to a more amber or green-gold shade. Older cats can also develop a condition called nuclear sclerosis that causes their eyes to look cloudy or bluish-gray.
Diseases
Certain diseases and medical conditions can cause a cat’s eye color to change. One of the most common is glaucoma, which is characterized by increased pressure in the eye. Glaucoma causes damage to the optic nerve and can lead to blindness if left untreated. As glaucoma progresses, the eye color may change and appear cloudy or bluish (1). This is due to damage to the iris and other structures in the eye. Medications like eye drops can help lower eye pressure and treat glaucoma. But in severe cases, surgery may be necessary (2).
Other diseases that can alter eye color include cataracts, which cause the lens to become cloudy. This gives the eyes a grayish, bluish color. Surgery to remove cataracts can potentially restore normal eye color (3). Inflammation inside the eye (uveitis) can also change eye color, giving the iris a darker, irregular appearance (4). Treatment involves medication to reduce inflammation. In the case of an injury, bleeding inside the eye (hyphema) can temporarily change the color. But once the blood is absorbed, the eye color generally returns to normal. If a cat’s eyes change color suddenly, it’s important to have a veterinarian examine them to diagnose and treat any underlying medical issue.
(1) https://trumannanimalclinic.com/2022/06/21/what-causes-my-cats-eyes-to-change-color/
(2) https://www.catster.com/lifestyle/what-causes-abnormal-eye-color-in-cats
(3) https://www.morrisanimalinn.com/blog/can-cats-eyes-change-color/
(4) https://www.petmd.com/cat/conditions/eyes/c_ct_uveitis
Injuries
Physical trauma or inflammation to a cat’s eye can cause temporary or permanent color changes in the iris. This is because injury and inflammation can cause blood congestion in the iris, leading to a darker reddish-brown discoloration. According to a Reddit user, their cat’s eye turned brown after an injury, likely due to blood congestion (Source). If the trauma or inflammation is severe enough, it can permanently damage the melanin pigment cells in the iris, resulting in a permanent color change.
Cats that get in fights are prone to eye injuries that can change their eye color. Scratches to the cornea from a cat fight can cause inflammation and bleeding that leads to temporary brown discoloration of the iris. If the injury causes permanent scarring or damage to the iris, the color change may be permanent. Owners should monitor their cats’ eyes for injuries and take them to a vet promptly for treatment to minimize permanent damage.
Nuclear Sclerosis
Nuclear sclerosis, also known as lenticular sclerosis, refers to the gradual hardening of the lens in a cat’s eye as it ages. This condition causes the lens to become cloudy or bluish-gray in color. According to VCA Animal Hospitals, nuclear sclerosis is common in cats over the age of 7 and eventually happens in most cats as they reach old age (1).
The cloudiness is caused by changes and hardening of the lens nucleus or center of the lens. Older fibers in the center of the lens lose water and become more compacted and dense. This increased density causes light to scatter and the lens to appear hazy and bluish-gray rather than clear (2).
While nuclear sclerosis may eventually cause some mild vision loss, it is not painful and does not necessarily impair vision significantly, especially in early stages. However, it is important to monitor for any rapid changes in vision or increased cloudiness, which could indicate a more serious eye condition (3). Overall, nuclear sclerosis is considered a normal age-related change in most cats.
Sources:
(1) https://vcahospitals.com/know-your-pet/lenticular-sclerosis-in-cats
(2) https://www.petcarerx.com/article/nuclear-sclerosis-in-cats/1311
(3) https://www.acvo.org/tips-treatments-tricks/signs-of-age-related-change-in-the-eye
Diagnosis
If you notice your cat’s eye color changing, it’s important to take them to the vet for an examination to determine the underlying cause. The vet will thoroughly examine your cat’s eyes to look for any abnormalities. They may perform various tests such as:
According to Truman Animal Clinic, the vet will use an ophthalmoscope to examine the retina and other structures in the back of the eye. This allows them to check for any retinal detachments, tumors or other issues that could be causing the color change.
They may also do a fluorescent staining test to check for corneal scratches or ulcers. This involves putting a special dye in the eye which will illuminate anydamage under a blue light.
Tests like tonometry and gonioscopy can help measure eye pressure and check for glaucoma, which can lead to eye color changes in cats.
Depending on the suspected cause, the vet may also run blood tests or do imaging tests like an MRI or CT scan. Biopsies of eye tissue may also be taken.
Once the underlying condition is diagnosed, the vet will recommend appropriate treatment to manage it. This may include eyedrops, surgery or medication. Prompt diagnosis and treatment can help restore eye health and prevent permanent damage leading to vision loss.
Conclusion
In summary, there are several key factors that can cause a cat’s iris to change color over time. Genetics and breed often determine the initial eye color, but this can evolve as the cat ages. Diseases like glaucoma or diabetes, injuries, and age-related conditions like nuclear sclerosis may also alter the appearance and color of the iris.
While some minor variations in eye color are normal, significant changes could signal an underlying medical issue. It’s important for cat owners to monitor their pet’s eyes and have any abnormalities checked by a veterinarian. Identifying and treating conditions early can help prevent vision loss and other complications.
By understanding the various reasons a cat’s eye color may change, owners can better spot potential health problems and ensure their cat’s eyes remain healthy.
