Category Kids Queries

Chickens have terrible night vision, but they’re capable of seeing colors – including vibrantly purple ultraviolet colors – that humans cannot. Researchers think chickens and other birds inherited their visual capabilities from their dinosaur ancestors. Because most dinosaurs weren’t nocturnal (active at night), they developed exceptional color perception and motion – detection vision for hunting a broad daylight.

 Chickens have very few cones, and they are not especially sensitive.  This difference between rod to cone ratio and the light sensitivities of cones in birds vs. mammals is explained because mammals all but disappeared from evolution long ago, and the only types of mammals that survived were nocturnal and insect eaters.  Mammals that survived this evolutionary bottleneck re-developed colour vision after millions of years, but since we evolved our cones from a different starting point than birds (they evolved from dinosaurs, and never spent millennia as nocturnal creatures), we developed our colour vision a little differently.  It’s another case of convergent evolution like whales and dolphins evolving to look like fish, because that’s the body type that works best in the water.

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Brown Eyes: Brown eyes are the most common eye color in the world with over 55% of the world’s population having brown eyes. Brown eye color is a dominant genetic trait, and is created by the presence of melanin in the eye. Brown eyes are typically darker than other eye colors, and they may even appear black in certain individuals.

Hazel Eyes: Hazel eyes are similar to brown eyes, although they are typically lighter in color, and have more of a green-yellow tint. Hazel eyes have a higher concentration of melanin (pigment) around the eye’s border, which can result in a multi-colored appearance that varies between copper and green depending on the lighting. Most people estimate that around 5-8% of the world’s population has hazel colored eyes.

Blue Eyes: Blue eyes are genetically recessive and therefore much less common worldwide. Blue eyes are formed by the absence of pigments in the eye, where the blue color is formed by the scattering of light as it’s reflected off the iris. It’s estimated that approximately 8% of the world’s population has blue eyes.

Green Eyes: Green eye color is often confused with hazel eye color, yet is entirely separate and distinct. Green eye color is the rarest color found around the world, and it is estimated that only around 2% of the world’s population has green colored eyes. Green eye color is a result of a mild amount of pigmentation in the eye with a golden tint. When combined with the natural blue scattering of the eye, the colors mix to give a green appearance.

Silver Eyes: Silver eye color is also quite rare, although many consider silver eyes to be a variation of blue eye color. Like blue eyes, silver eyes are the result of a very low amount of pigmentation in the eye, which reflects a gray-silver appearance.

Amber Eyes: Amber eyes show off a yellow-copper tone, which results from the yellow colored pigment lipochrome. Amber eye color can range from golden yellow to a more copper tone.

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Sometimes, a person’s melanin pigment doesn’t spread evenly to each iris. Which can lead to one eye being darker than the other or even splashes of color in each iris? This extremely rare condition – known as heterochromia – doesn’t affect a person’s vision.

Heterochromia can be either present from birth (congenital) or acquired. Most people will have someone else in their family with the same condition, although if it develops at an early age it’s still considered to be congenital.

Acquired heterochromia can occur either from injury or illness, but won’t be the cause of any difficulty with vision. If any parts of your iris does change colour make sure you visit an ophthalmologist, just to be on the safe side.

Your eye colour is set by a variety of genes, but heterochromia occurs due to the concentration and distribution of a pigment called melanin. Melanin is also important in determining what colour skin you have and is found in your hair too.

It’s known that blue eyes contain the lowest amount of melanin, whereas brown eyes have the most, and so heterochromia is caused from one eye having either considerably more or considerably less melanin than the other.

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Eyelashes have one main purpose — protecting your eyes. They help to keep dirt, germs, and other stuff out of your eyes, which are very delicate and need to be kept clean! Our eyelashes also help us know when a foreign object is headed towards our eye – when they sense the touch of some dirt or dust, they quickly send us the message to shut our eye and keep out the invader! 

Like the hair on your head, eyelashes sometimes naturally fall out and naturally grow back, too. It takes approximately four to six weeks for an eyelash that has fallen out to grow back, although because you have so many, it’s unlikely you’ll ever even notice it was gone! And don’t forget – when an eyelash lands on your cheek, pick it up, blow it away, and make a special wish!

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Your retina is covered with millions of special cells called rods and cones that process light from the lens. Cones detect colors (people who are colour blind are missing cone cells for a particular color), while the rods process light information. Scientists can guess at how animals perceive vision by counting the rods and cones in their eyes. Cats, for instance, have eight times as many rods as humans but far fewer cones, which explain their excellent night vision and their relative color blindness.

Photoreceptors cells take light focused by the cornea and lens and convert it into chemical and nervous signals which are transported to visual centers in the brain by way of the optic nerve.

In the visual cortex of the brain (which, ironically, is located in the back of the brain), these signals are converted into images and visual perceptions.

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CORNEA: The eye’s protective, transparent cover, the cornea is similar to the protective glass on a camera lens. It bends the light entering your eye to pre – focus the image before it reaches your lens.

PUPIL: Muscles in the iris control this hole in the center, which, like a camera’s shutter, allows light to enter the eye and strike the lens. In bright sunlight, the pupil contracts to let in less light. In darkness, it opens wide to let in as much light as possible.

SCLERA:  The whites of your eyes, sclera from a protective cover about the size of a ping – pong ball.

LENS: Like a projector in a moving theater, the lens focuses light onto the retina. It’s suspended in a muscle that changes the shape of the lens to focus on objects near and far faster than any computerized camera.

OPTIC NERVE: This cable carries visual information from your retina to the brain. Your brain processes the information and translates it into what you’re actually seeing.

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