Introduction
With their elliptical pupils and nocturnal nature, Felis catus (the domestic cat) have an appearance that can seem mysterious and even creepy at times. There’s a popular myth that cat eyes operate just like snake eyes do, with scary night vision abilities and creepy stares. But just how much truth is there to this legend? What makes cat eyes look the way they do, and how similar are they really to snake eyes? In this article, we will explore the anatomy and adaptations behind feline eyes, comparing them side-by-side with serpent eyes to separate myth from reality.
Anatomy of Cat Eyes
Cats have a complex eye structure adapted for hunting. The major components of cat eyes include:
- Iris – The colored part of the eye. It controls the amount of light entering the eye by dilating and constricting the pupil.
- Pupil – The black opening in the center of the iris. It changes size to regulate light levels entering the eye.
- Retina – Contains photoreceptors (rods and cones) that detect light and convert it into signals to the brain, allowing cats to see. The area centralis region has the highest concentration of photoreceptors.
- Cornea – The clear outer layer that helps focus light onto the retina.
- Lens – Focuses images onto the retina. Its shape can change to enable cats to see objects at varying distances clearly.
Cats have evolved excellent vision adapted for hunting. Their eyes contain a high concentration of rod photoreceptors, allowing them to see well in dim light. The rectangular pupils enable precise control over light levels entering the eyes. Cats also have a visual streak area in their retina with a high concentration of photoreceptors optimized for detecting fast movements. This helps cats spot and catch prey.
Sources:
https://www.merckvetmanual.com/cat-owners/eye-disorders-of-cats/eye-structure-and-function-in-cats
Anatomy of Snake Eyes
Snakes have unique eye anatomy that has evolved for their specific needs as predators. Unlike many animals, snakes lack movable eyelids and instead have a clear scale called a spectacle that protects their eyes (Snake Ocular Anatomy, https://czar.vetmed.ucdavis.edu/research/snake-ocular-anatomy). The spectacle is a transparent scale that covers the eye like a contact lens and can be shed and regenerated along with the rest of the snake’s skin.
Inside the eye, snakes have a round pupil that can open wide to let in light. Their retina contains two types of light-sensing cells (rods for dim light, cones for color vision) as well as a reflective layer called the tapetum lucidum that improves night vision by bouncing light back onto the retina. The lens of the snake eye is spherical and fixed in place, unlike the adjustable lenses in human eyes. Snakes are able to focus by moving their retina forward and backward to achieve sharp vision (Snakes’ eyes could give us super eyesight, https://www.sciencenordic.com/animals-biology-denmark/snakes-eyes-could-give-us-super-eyesight/1430322).
The unique structures of the snake eye evolved to meet their needs as hunters. Lack of eyelids and a spectacle scale protect the eyes and maintain clarity while allowing snakes to see well in dim light. Wide pupils and a mobile retina also enhance vision in dark or varied environments.
Night Vision
Both cats and snakes have excellent night vision compared to humans, thanks to special adaptations in their eyes. One key adaptation is the tapetum lucidum, a reflective layer behind the retina that bounces light back through the photoreceptors, essentially giving light a second chance to be detected. This boosts low-light sensitivity significantly. Cats have a tapetum lucidum which gives their eyes a distinctive shine in the dark when light reflects off it. Snakes also possess this layer, which helps them hunt successfully at night.
In addition, cats have a high proportion of rods in their retinas, which are the photoreceptors responsible for low-light vision. They have excellent night vision, with some estimates putting their low-light vision at 6-8 times better than humans. Snakes also tend to have a large number of rod cells, giving them very good night vision as well. For example, pit vipers have been found to have rod densities 10 times higher than humans.
Slit Pupils
Both cats and snakes have slit-shaped pupils that are vertical when fully open and constrict to narrow slits in bright light. According to sciencefocus.com, the slit pupils of cats and snakes allow them to “control the amount of light entering the eye in very bright conditions,” protecting their sensitive retinas. The vertical slit shape is an adaptation for predators seeking prey. Source
The vertical slit pupil gives cats and snakes several advantages for vision as predators. The narrow slit can open wide in dim light, allowing more light in to see prey. The slit also reduces aberrations, which allows for sharper focus on prey. Additionally, the slit gives cats and snakes panoramic vision for detecting prey movement. According to reddit.com discussions, the vertical slit pupil optimizes light regulation and visual acuity for the hunting needs of cats and snakes. Source
Eye Color
Eye color in cats and snakes shows significant variation, with eyes ranging from shades of blue, green, yellow, brown, and multiple combinations. According to Quora, black and white cats frequently have green eyes, although other colors like tabby are more common overall. Snakes like pythons tend to have a yellowish eye color. Eye color is determined primarily by genetics, specifically the amount and type of melanin pigments. More melanin leads to darker colors like brown, while less melanin produces blue and green shades. The specific genes involved in eye color are complex and not fully understood, but influence the production and distribution of melanin. While eye color between cats and snakes overlaps, the genetic mechanisms differ somewhat between mammals and reptiles.
Peripheral Vision
Cats and snakes share similar peripheral vision adaptations that give them an edge when hunting prey. While humans have a visual field of around 180-200 degrees, cats have a wider visual field of about 285 degrees (Venkataraman, 2022). Snakes have an even wider visual field, with some species like pythons having a visual field up to 270 degrees on each side, giving them a panoramic view of nearly 360 degrees (Rasmussen et al., 1993).
The key benefit of this extended peripheral vision in cats and snakes is that it allows them to spot potential prey across a wide area without having to move their heads. As ambush predators, snakes rely on detecting small movements of nearby prey like mice or lizards using their sensitive peripheral vision. Similarly, cats use their wide visual field to notice any birds, rodents or insects moving at the edges of their vision. This allows them to swiftly attack from any direction (Rasmussen et al., 1993).
Overall, the extensive peripheral vision of cats and snakes provides a major hunting advantage by enhancing their ability to detect and target prey animals in their vicinity.
Sources:
Venkataraman, V. (2022). TIL the reason cats and snakes have vertical pupils is because it increases their depth perception while hunting at night while prey animals …. Reddit. Retrieved from https://www.reddit.com/r/todayilearned/comments/9s8hc0/til_the_reason_cats_and_snakes_have_vertical/
Rasmussen, A. R., Murphy, J. B., & Ompi, M. (1993). Marine toads and venomous snakes: misperceptions of risk by prey and predators. Journal of Herpetology, 27(4), 477-481.
Eye Shine
Eye shine in cats and snakes is caused by a reflective layer of tissue in the eye called the tapetum lucidum. This layer sits behind the retina and reflects visible light back through the retina, giving cat and snake eyes a distinctive shine or glow in low light conditions.
The tapetum lucidum enhances vision at night by allowing the light-sensing cells in the retina a “second chance” to be stimulated by light rays. This aids cats and snakes with night vision and the ability to hunt prey at dawn, dusk, and in darkness [1].
The eyeshine in cats and snakes can appear yellow, green, orange or red depending on the species. This is because the tapetum lucidum reflects light back through the retina, and the specific color depends on which wavelengths of light are being reflected most strongly.
So in summary, the eye shine or glow seen in cats and snakes at night is caused by the tapetum lucidum – a specialised retinal structure evolved to enhance their vision in low light conditions for hunting.[2]
Myths vs Reality
There are a few common myths and misconceptions when it comes to cat and snake eyes:
Myth: All cats have vertical slit pupils like snakes. In reality, only about 40% of cats have slit pupils, while the other 60% have round pupils like humans. Large wild cats like lions and tigers actually have round pupils.
Myth: Venomous snakes always have slit pupils. In fact, many highly venomous snakes like cobras, mambas, and kraits have round pupils. Pupil shape alone does not indicate whether a snake is venomous or not.
Myth: Cats and snakes have excellent night vision. While it’s true their eyes are adapted for low light, they cannot see perfectly in complete darkness and their night vision capabilities are often exaggerated.
Overall, while cat and snake eyes share some similarities like vertical pupils, assumptions about their vision or nature based on eye shape alone tends to be unreliable or exaggerated. Looking at confirmed facts and research helps clarify truths vs myths.
Conclusion
In summary, while cat and snake eyes share some similarities like vertical slit pupils and specialized structures for night vision, they differ significantly in their anatomy and functionality. Cats have round pupils that can constrict to vertical slits, while snakes have permanently elongated vertical pupils. Both allow for precise focusing on prey. However, cats are not as adept as snakes at sensing infrared radiation through specialized pit organs. Additionally, the retina and optic nerves in cats are oriented differently than snakes to support better peripheral vision.
When examining the totality of evidence, it is clear that cat eyes do not truly resemble snake eyes despite a passing similarity in their slit-like pupils. The unique combination of optics, retina, and brain processing in cats produces their distinctive feline gaze that is optimized for hunting small, fast-moving prey. While some parallel functionality exists between these predatory creatures, cat eyes remain distinctly feline.
