Cat Night Vision Vs Human - Cat Lovers Hub

Cats are known for their excellent night vision abilities compared to humans. In low light conditions, cats can see much better than humans due to key differences in the anatomy and physiology of their eyes. This article explores the science behind cat and human low light vision, including a comparison of factors like anatomy, field of view, color perception, and motion detection. The goal is to help explain why cats can see so well in the dark compared to humans.

Table of Contents

Anatomy of Cat Eyes

Cats have a unique structure to their eyes that allows them to see well in low light conditions. One of the key elements is the tapetum lucidum, a reflective layer of tissue in the eye that sits behind the retina.

The tapetum lucidum acts like a mirror, reflecting light back through the retina and giving light particles a second chance to be detected by the photoreceptors. This allows cats to make the most of low light situations. It’s why cat eyes seem to glow in the dark when light shines on them.

Cats also have a high density of rods in their retina, which are the photoreceptors responsible for low light vision. They have 6-8 times more rods than humans do. Their rods are also located throughout the retina, while human rods are concentrated on the periphery. This gives cats superior low light vision and motion detection.

Additionally, cats have vertical slit pupils that can open wide to let in more light. All of these adaptations allow cats to see well in the dark to hunt at night.

Source: https://www.merckvetmanual.com/cat-owners/eye-disorders-of-cats/eye-structure-and-function-in-cats

Anatomy of Human Eyes

The human eye has several parts that work together to enable vision. Some key parts include the cornea, iris, pupil, lens, retina, macula, optic nerve, and more. The cornea is the clear front layer that helps focus light. Behind it, the iris is the colored part that controls pupil size to regulate light entering the eye. The pupil is the black opening in the center of the iris that allows light in. The lens sits behind the pupil and focuses light onto the back of the eye called the retina. The retina contains photoreceptor cells that convert light into signals sent to the brain via the optic nerve. An important part of the retina is the macula which gives central, high resolution vision.

One key difference between cat and human eyes is that humans lack a tapetum lucidum. This is a reflective layer behind the retina in many animals like cats that helps reflecting light back through the retina to enhance vision in low light. Humans do not have this adaptation, meaning our night vision capabilities are more limited compared to cats and other animals with a tapetum lucidum.

Sources:

https://www.aao.org/eye-health/anatomy/parts-of-eye

https://www.umkelloggeye.org/conditions-treatments/anatomy-eye

Low Light Vision in Cats

Cats have excellent low light vision due to the high number of rods in their eyes. Rods are photoreceptor cells in the retina that allow vision in low light conditions. Cats have a high ratio of rods to cones (photoreceptor cells that distinguish color) which gives them superior low light sensitivity but poorer color vision (Purina, 2022).

The structure of the feline eye also contributes to their ability to see in the dark. Cats have an additional reflective layer behind the retina called the tapetum lucidum. This layer reflects light back through the retina, essentially giving light a second chance to be detected by photoreceptors. This boosts cats’ low light vision significantly (Hill’s Pet Nutrition, 2021).

Additionally, cats can open their pupils very wide to allow more light to enter the eye. Their pupils can dilate to cover nearly the entire visible part of the eyeball, greatly enhancing light capture in dark conditions.

Low Light Vision in Humans

Unlike cats, human eyes rely primarily on cone photoreceptor cells for vision in normal daylight conditions. Cones allow humans to see color and fine details (Wikipedia, 2023). However, cones require a lot of light to function properly.

In low light conditions, the human eye shifts to using rod photoreceptor cells which are much more sensitive to light. However, rods do not detect color very well. This is why human night vision lacks color perception and appears dimmer with less clarity (Cleveland Clinic, 2022).

The shift from cones to rods for night vision is called “scotopic vision” and it reduces visual acuity significantly. With only 5-10% as many cones as rods, humans rely heavily on rods for night vision. But with lower density and sensitivity, scotopic rod vision in humans is still far inferior to cats (Cleveland Clinic, 2022).

Color Perception Differences

Cats and humans see color differently. Humans have trichromatic vision which means we have three types of color receptors (cones) that allow us to see red, green and blue light. This gives us good color vision across the visible light spectrum. According to Business Insider, cats are dichromatic, meaning they have only two types of cones. This means their color vision is limited compared to humans.

Scientists believe cats can see some colors in the blue and green range, but reds and oranges appear more green, and colors like purple and gray do not appear distinct from other colors. Essentially, cats see a far less vibrant, saturated color palette than humans. While we see the full spectrum, cat color vision is muted and blurry. This is likely an evolutionary adaptation to support their excellent night vision, as The Purrington Post explains.

Field of View Comparison

Cats have a significantly wider field of view compared to humans. A cat’s field of view is about 200 degrees, while the average human field of view is only 180 degrees (1). This means cats can see almost all the way behind themselves without turning their heads. Their wider field of view gives cats a larger visual range to detect potential threats or prey.

Cats’ eyes are positioned more to the sides of their heads, enabling this panoramic vision. Humans have a more binocular field of vision, with both eyes facing forward. While cats gain a wider visual field, their depth perception is reduced compared to humans (2).

Overall, a cat’s 200 degree field of view gives them superior awareness of their surroundings. However, they lose some visual acuity and depth perception compared to human vision with a narrower 180 degree field of view.

Motion Detection

Cats have superior motion detection abilities compared to humans, especially in low light conditions. Cats can detect movement at much greater distances and with more precision than humans due to differences in their visual systems.

A key factor is the high density of rod photoreceptor cells in cat retinas, which allow them to detect even tiny movements in their peripheral vision. Cats also have a higher flicker fusion rate, meaning they can perceive rapid changes in movement better than humans ^[1]. Their elliptical pupils further assist motion detection by controlling light levels entering the eye.

In contrast, humans rely more heavily on cone cells for central, color vision. We have far fewer rod cells, especially in our peripheral vision. This makes us less adept at noticing quick motion at the edges of our field of view. Cats can detect movement from distances over 20 times farther away than humans.

As a result, motion sensors designed for humans like those used in home security systems will often get falsely triggered by pets. Sensors specifically calibrated to detect human body heat signatures rather than all motion work better in households with cats ^[1].

Conclusion

Cats and humans have evolved very different visual systems to adapt to their respective environments and lifestyles. Cats have excellent night vision and motion detection which allows them to hunt at night, but more limited color perception and field of view. Humans evolved color vision and excellent detail perception needed for tasks like reading, but much poorer night vision. These differences highlight how our sensory capabilities are shaped by how we use them. Going forward, we can apply knowledge of cat and human vision to design environments, devices, and experiences optimized for each species’ visual strengths. Understanding species differences allows us to provide the best care for our feline companions, meet their visual needs, and enrich the human-animal bond.