The Feline Eye(s)

Feline Eyesight: Day and Night

1. Tapetum Lucidum: This is a layer of cells in the cat's eyes that reflects light back through the retina. It gives cat eyes their characteristic shine when they catch the light. This reflective quality amplifies the amount of light the eyes can capture, enabling better vision in low-light conditions, such as nighttime.

2. Rods and Cones: Like humans, cats have rods and cones in their retinas. Rods are photoreceptor cells responsible for low-light vision, while cones provide color vision in brighter light. Cats have more rods than humans, which also contributes to their excellent night vision.

3. Pupil Shape: A cat's pupil is vertically slit-shaped and can open extremely wide in dim light to allow as much light as possible into the eye. This contrasts with the round pupils found in humans and some other animals. In bright light, the slits narrow to protect the sensitive retina.

4. Field of View: While humans have about a 180-degree field of view, cats have a slightly wider field at approximately 200 degrees. This gives them a broader view of their environment, which is especially helpful when hunting.

5. Color Vision: Cats don't see color the same way humans do. It's believed that cats can see blue and green but have difficulty distinguishing reds and pinks. This is because they have fewer cone cells in their retinas compared to humans.

6. Acuity: Cats may not have the same level of detail vision as humans. In terms of acuity, a cat's vision might be in the 20/100 to 20/200 range. This means that what a cat can see clearly at 20 feet, a human with perfect vision could see clearly from 100 to 200 feet away.

Eye Color and Genetics:

1. Basic Genetics: Eye color in felines is a result of the presence and concentration of melanin, the pigment responsible for coloration in both the iris and fur.

2. Kittens: All kittens are born with blue eyes. As they grow, the melanin concentration in their eyes changes, and by the time they are three months old, their true eye color starts to emerge.

3. Eye Color Range: Most cats have shades of green, gold, or yellow eyes. Blue eyes can be found in certain breeds, especially those with white or Siamese markings. Odd-eyed or heterochromia is a condition where a cat has two differently colored eyes, often seen in white cats.

4. Genetic Factors: Different genes dictate coat color and eye color in felines. However, there is a correlation. For example, white cats with blue eyes are often deaf. In Siamese cats, the enzyme responsible for pigment production is temperature-sensitive. This results in darker colors (points) on the cooler parts of their bodies (ears, paws, tail) and blue eyes.

5. Breed Specifics: Some breeds have a more narrow range of acceptable eye colors in show standards. For example, British Shorthairs are known for deep gold or copper eyes, while Russian Blues have striking green eyes.

Eye Color in Felines

Eye color in felines, like many traits, is influenced by multiple genetic factors. Some genes directly influence eye color, while others have indirect effects. The primary driver of eye color is the distribution and density of melanin within the iris. Here’s a breakdown of the nuances of feline eye color and the genetics involved:

1. Melanin and Eye Color:

   • Blue Eyes: 

Cats' eyes are blue as kittens because they haven't developed the melanin pigment yet. Most will change to a different color as they grow, but some cats retain this blue hue.

Blue eyes are generally associated with a lack of melanin in the iris, leading to the scattering of light in a way that makes the eyes appear blue.

Certain breeds, such as Siamese, have a genetic predisposition to blue eyes. The gene responsible for the Siamese coat pattern, a form of partial albinism, also affects eye color. This gene is referred to as the Himalayan gene or the cs allele.

1. • Green Eyes: 

Green eyes in cats are the result of a medium amount of melanin in the iris.

It is not entirely clear which specific genes result in green eyes, but it is a combination of genetics, the scattering of light, and the type and amount of melanin present.

Breeds like Russian Blue are often associated with green eyes.

1. • Yellow or Gold Eyes: 

Gold and yellow eyes are due to a higher concentration of melanin than found in green or blue eyes but not as much as in brown eyes.

The richness and depth of the gold or yellow hue depend on the amount of melanin present.

Again, the specific genes responsible for these colors are not entirely clear, but it's known that melanocyte-stimulating hormone (MSH) can stimulate the production of melanin, thus influencing eye color.

1. • Copper or Amber Eyes: 

These eye colors are similar to gold but may have a deeper hue due to the presence of more melanin.

Breeds like the British Shorthair might exhibit these colors.

1. • Brown Eyes: 

Brown eyes in cats are less common than in humans. When they do appear, it's usually due to a very high concentration of melanin.

Breeds like the Burmese are associated with deeper eye colors.

2. White Cats and Eye Color:

   • Cats with a completely white coat can have blue, amber, or green eyes. The gene responsible for white coat (the W gene) can sometimes also impact hearing, leading to the known correlation between blue-eyed white cats and deafness.

3. Breed-specific Eye Colors and Genetics:

   • Siamese and Related Breeds: The pointed pattern (darker ears, face, paws, and tail) in breeds like the Siamese is due to a temperature-sensitive enzyme that affects melanin production. These breeds often have striking blue eyes due to the same genetic factor.

   • Burmese: These cats carry a gene that gives them a solid sepia-toned coat and typically results in gold or yellow eyes.

4. Heterochromia:

   • This is when a cat has two differently colored eyes. While the exact cause can vary, one common reason in white cats is the presence of the white (W) gene, which can lead to one blue eye and one green or gold eye. It can also be found in non-white cats.

5. Polygenes:

   • Beyond specific identified genes, there are likely many minor genes (polygenes) that play roles in determining the exact shade of a cat’s eyes. These genes have smaller effects on their own but can collectively shape traits in complex ways.

While many genes affecting coat color in cats have been identified and studied in detail, the exact genes and mechanisms behind all the nuances of feline eye color are not yet fully understood. In many cases, breeders rely on empirical knowledge – that is, they know that breeding two cats with certain characteristics often results in kittens with certain eye colors, even if the specific genetic mechanisms are not clear. As genetics research continues, more insights will undoubtedly emerge about the intricate dance of genes that determines a cat’s eye color.

What are common genes that can cause blue eyes in feline?

1. The Himalayan Gene (cs allele):

   • This gene is responsible for the color point pattern seen in Siamese, Himalayan, and other related breeds. Cats with this gene have a form of partial albinism which restricts the distribution of pigment along the cooler parts of their body, resulting in the characteristic color points on the ears, face, paws, and tail. This same gene also affects eye color, typically resulting in blue eyes.

2. White Coat Gene (W):

   • Cats that are completely white, whether they are true albinos or not, often have blue eyes. This is because the gene responsible for white coat color can also affect the pigmentation in the eyes. Some white cats have one or both eyes blue due to the white coat gene. Turkish Angoras and other white breeds can exhibit this trait.

3. Ojos Azules Gene:

   • "Ojos Azules" is a relatively rare breed of cat, and they are known for their deep blue eyes. Interestingly, cats of this breed can have any coat color and still have blue eyes. The genetic mutation responsible for this is distinct from the Himalayan gene and the white coat gene. However, this gene has been associated with some severe health issues, so breeding these cats is controversial.

4. Heterochromia:

   • While not a gene for blue eyes per se, some cats have heterochromia, meaning each eye is a different color. One of these eyes can be blue, even in cats that do not carry any of the genes typically associated with blue eyes. This condition can be genetic, but it can also result from injury, illness, or other developmental factors.

In addition to the genes mentioned above, it's essential to understand that the genetics of feline eye color is complex and still not fully understood. There are likely other genes and modifiers at play that haven't been identified or studied in depth. The interaction of multiple genes, as well as environmental and developmental factors, can contribute to the eye color outcome in individual cats.