Why Do Cats Have Better Night Vision Than Humans? Unveiling the Secrets of Cat Night Vision
Why Do Cats Have Better Night Vision Than Humans? Unveiling the Secrets of Cat Night Vision
Cats, as members of the top predator family, possess extraordinary vision. They use this sense to target prey, something ordinary humans are incapable of doing. This visual ability of cats is highly active at night and in low-light conditions. It's a characteristic that felines have in the wild for hunting, and therefore, they can also hunt after the sun sets. Felines have night vision that is one hundred times keener than human sight.
How Does Vision Occur?
When an organism "sees" something, the truth is that its eyes aren't actually "seeing." The brain is the primary organ that provides meaning to the different electrical impulses it receives from the eyes. Whether it's a cat's eye or a human eye, they are simply tools for gathering "visual" information. This information is transmitted through the optic nerve to the cat's occipital lobe. The occipital lobe processes this visual information while also receiving information from other parts of the brain. Once this process is complete, the cat is able to form a "meaning" of what it "sees."
The eyes receive light waves from the environment. These light waves enter the front of the eye and travel toward the back. In the process, the light passes through different structures such as the cornea, pupil, lens, and retina. Each structure has a very specific function to help gather light or visual information.
cornea, iris, ciliary body, lens, anterior chamber, retina
fitration angle, vitreous body, optic nerve, optic disk
The cornea is the outer layer of the eye and acts as a protective membrane for the other structures inside the eye. The pupil is like a window that adjusts the amount of light that enters by changing the size of the opening. If it's too dark, meaning there are fewer light waves entering the eye, then the pupil will have to dilate to allow more light to enter. If it's too bright outside, the pupil will try to minimize the size of the opening. This is to help reduce the amount of light entering.
When light passes through the pupil, it hits the lens, which reflects the light to the target organ in the back of the eye. The lens also attempts to regulate the amount of light that gets refracted to the retina. It can make its shape more concave or convex, trying to transmit the appropriate amount of light to the back of the eye.
The retina is where the light waves that enter the eye end. It's also the part of the cat's eye that is responsible for their extraordinary vision. The retina contains two types of photoreceptor cells or light receptors. These are the cones and rods. Cone cells are responsible for color vision. They also help with daytime vision. When observing in the dark or in low-light conditions, it's the rod cells' responsibility. These photoreceptor cells are highly sensitive to different shades of gray and different levels of brightness. Rod cells are also the photoreceptor cells that are responsible for peripheral vision.
Photoreceptor cells, whether rods or cones, convert light into nerve impulses. These receptors send these electrical signals to the thalamus through the optic nerve. Nerve impulses travel from there all the way to the occipital lobe. Here, the nerve impulses are processed into visual information. The neurons in the occipital lobe pass the "processed" image to the parietal lobe, where the image is "interpreted."
Differences in Night Vision Between Cats and Humans
Based on the discussion above, the primary structural basis for seeing things in the dark is the rod cells. These photoreceptor cells are highly sensitive to brightness, shades of gray, peripheral vision, and night vision.
However, rod cells are present in the retina of almost all organisms. This includes cats, dogs, and humans. Does this mean that a cat's ability to see in the dark is similar to our ability to see in low-light conditions? This is not the case. There are several anatomical differences between human eyes and cat eyes. Here are some of the main differences:
(a) More Rod Cells than Cones
As mentioned earlier, rods are crucial when it comes to gathering low-light information. Theoretically, the more rod cells an organism has, the better it is at seeing in the dark. However, this structure in a cat's eye contains more rods than cones. This is also the reason why cats are not good at distinguishing colors because cones are responsible for color vision.
Because felines have more rods in their retinas, they don't need as much light to produce nerve impulses and send them to the brain. Instead, they only need about one-sixth of the light that a human eye would need in similar circumstances. For example, if you need at least 1 lumen of light to be able to see your way around, then a cat only needs about 1/6 lumen to see what you're seeing.
(b) Cats Have a Wider Field of Vision
One important function of the rod cells is peripheral vision. Rod cells are usually found on the outer edge or periphery of the retina. This gives cats a wider field of vision compared to humans. Humans have a maximum field of vision of only 180 degrees. However, cats can have a field of vision of up to 300 degrees. Each of the cat's eyes provides a 155 to 208 degree field of vision. When it comes to cat night vision, the wider field of vision allows it to scan the surroundings more effectively, making it possible for cats to see prey and predators in the dark.
(c) The Transparent Tapetum Lucidum
There's a very important structure in the cat's eye that humans don't have, the transparent tapetum lucidum located behind the retina. This is a very thin layer of tissue that acts as a reflective layer. Its function is to reflect light back to the retina where the photoreceptor cells are found. This structure is common in nocturnal animals and deep-sea creatures.
When the lens transmits light to the retina, some of the light may possibly pass beyond the retina. Because the tapetum lucidum is behind the retina, it reflects the stray light back to the retina. This can enhance the cat's night vision because there's now more light to stimulate the photoreceptor cells. Identifying the tapetum lucidum in a cat is very easy. In low-light conditions, the tapetum lucidum is what we call a "cat's eye" or "eye shine."
(d) Vertical Orientation of the Pupil
The pupil is an important structure in the eye. The pupil regulates the amount of light that enters the eye. It will change the size of its opening depending on the light in the surroundings.
Human pupils are round. Cat pupils are more elliptical. They are also oriented more vertically. This makes the pupil much larger than that of a human. The larger the pupil opening, the more light enters the eye. From a narrow (small opening) state, human pupils can only dilate 15 times. In comparison, cat pupils can dilate anywhere from 130 to 300 times. This wide opening allows more light to enter. No matter how faint the light source, a cat's wide-open pupil can still gather enough light to transmit to the retina.
These four main features are what make it have a much better night vision than that of humans in the dark. A pupil that is larger than a human's allows more light to enter the eye, no matter how faint the light is. When the light reaches the retina, the increased number of rods facilitates the production of nerve impulses and transmit them to the brain. Because there are more rods, they also provide a wider field of vision. This is important in improving night vision. To ensure that light doesn't escape from the retina, the reflective layer will reflect the escaped light back.
Cats, as members of the top predator family, possess extraordinary vision. They use this sense to target prey, something ordinary humans are incapable of doing. This visual ability of cats is highly active at night and in low-light conditions. It's a characteristic that felines have in the wild for hunting, and therefore, they can also hunt after the sun sets. Felines have night vision that is one hundred times keener than human sight.
How Does Vision Occur?
When an organism "sees" something, the truth is that its eyes aren't actually "seeing." The brain is the primary organ that provides meaning to the different electrical impulses it receives from the eyes. Whether it's a cat's eye or a human eye, they are simply tools for gathering "visual" information. This information is transmitted through the optic nerve to the cat's occipital lobe. The occipital lobe processes this visual information while also receiving information from other parts of the brain. Once this process is complete, the cat is able to form a "meaning" of what it "sees."
The eyes receive light waves from the environment. These light waves enter the front of the eye and travel toward the back. In the process, the light passes through different structures such as the cornea, pupil, lens, and retina. Each structure has a very specific function to help gather light or visual information.
cornea, iris, ciliary body, lens, anterior chamber, retina
fitration angle, vitreous body, optic nerve, optic disk
The cornea is the outer layer of the eye and acts as a protective membrane for the other structures inside the eye. The pupil is like a window that adjusts the amount of light that enters by changing the size of the opening. If it's too dark, meaning there are fewer light waves entering the eye, then the pupil will have to dilate to allow more light to enter. If it's too bright outside, the pupil will try to minimize the size of the opening. This is to help reduce the amount of light entering.
When light passes through the pupil, it hits the lens, which reflects the light to the target organ in the back of the eye. The lens also attempts to regulate the amount of light that gets refracted to the retina. It can make its shape more concave or convex, trying to transmit the appropriate amount of light to the back of the eye.
The retina is where the light waves that enter the eye end. It's also the part of the cat's eye that is responsible for their extraordinary vision. The retina contains two types of photoreceptor cells or light receptors. These are the cones and rods. Cone cells are responsible for color vision. They also help with daytime vision. When observing in the dark or in low-light conditions, it's the rod cells' responsibility. These photoreceptor cells are highly sensitive to different shades of gray and different levels of brightness. Rod cells are also the photoreceptor cells that are responsible for peripheral vision.
Photoreceptor cells, whether rods or cones, convert light into nerve impulses. These receptors send these electrical signals to the thalamus through the optic nerve. Nerve impulses travel from there all the way to the occipital lobe. Here, the nerve impulses are processed into visual information. The neurons in the occipital lobe pass the "processed" image to the parietal lobe, where the image is "interpreted."
Differences in Night Vision Between Cats and Humans
Based on the discussion above, the primary structural basis for seeing things in the dark is the rod cells. These photoreceptor cells are highly sensitive to brightness, shades of gray, peripheral vision, and night vision.
However, rod cells are present in the retina of almost all organisms. This includes cats, dogs, and humans. Does this mean that a cat's ability to see in the dark is similar to our ability to see in low-light conditions? This is not the case. There are several anatomical differences between human eyes and cat eyes. Here are some of the main differences:
(a) More Rod Cells than Cones
As mentioned earlier, rods are crucial when it comes to gathering low-light information. Theoretically, the more rod cells an organism has, the better it is at seeing in the dark. However, this structure in a cat's eye contains more rods than cones. This is also the reason why cats are not good at distinguishing colors because cones are responsible for color vision.
Because felines have more rods in their retinas, they don't need as much light to produce nerve impulses and send them to the brain. Instead, they only need about one-sixth of the light that a human eye would need in similar circumstances. For example, if you need at least 1 lumen of light to be able to see your way around, then a cat only needs about 1/6 lumen to see what you're seeing.
(b) Cats Have a Wider Field of Vision
One important function of the rod cells is peripheral vision. Rod cells are usually found on the outer edge or periphery of the retina. This gives cats a wider field of vision compared to humans. Humans have a maximum field of vision of only 180 degrees. However, cats can have a field of vision of up to 300 degrees. Each of the cat's eyes provides a 155 to 208 degree field of vision. When it comes to cat night vision, the wider field of vision allows it to scan the surroundings more effectively, making it possible for cats to see prey and predators in the dark.
(c) The Transparent Tapetum Lucidum
There's a very important structure in the cat's eye that humans don't have, the transparent tapetum lucidum located behind the retina. This is a very thin layer of tissue that acts as a reflective layer. Its function is to reflect light back to the retina where the photoreceptor cells are found. This structure is common in nocturnal animals and deep-sea creatures.
When the lens transmits light to the retina, some of the light may possibly pass beyond the retina. Because the tapetum lucidum is behind the retina, it reflects the stray light back to the retina. This can enhance the cat's night vision because there's now more light to stimulate the photoreceptor cells. Identifying the tapetum lucidum in a cat is very easy. In low-light conditions, the tapetum lucidum is what we call a "cat's eye" or "eye shine."
(d) Vertical Orientation of the Pupil
The pupil is an important structure in the eye. The pupil regulates the amount of light that enters the eye. It will change the size of its opening depending on the light in the surroundings.
Human pupils are round. Cat pupils are more elliptical. They are also oriented more vertically. This makes the pupil much larger than that of a human. The larger the pupil opening, the more light enters the eye. From a narrow (small opening) state, human pupils can only dilate 15 times. In comparison, cat pupils can dilate anywhere from 130 to 300 times. This wide opening allows more light to enter. No matter how faint the light source, a cat's wide-open pupil can still gather enough light to transmit to the retina.
These four main features are what make it have a much better night vision than that of humans in the dark. A pupil that is larger than a human's allows more light to enter the eye, no matter how faint the light is. When the light reaches the retina, the increased number of rods facilitates the production of nerve impulses and transmit them to the brain. Because there are more rods, they also provide a wider field of vision. This is important in improving night vision. To ensure that light doesn't escape from the retina, the reflective layer will reflect the escaped light back.
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