Sight and Vision
You might think your eyes work like perfect little video cameras, but the truth is much stranger. Did you know that the images projected onto the back of your eye are actually completely upside down?
How Does Your Brain See the World?
It is completely upside down! Your brain takes the upside down images from both eyes, turns them right side up, mixes them together, and makes sense of what you see.
To give us depth perception and let us see in 3-D. Because your eyes are spaced slightly apart, they send two slightly different pictures to your brain. Your brain fuses these together to figure out how far away objects are!
Put Your Instincts to the Test
Think about what you already know about your eyes. Pick an answer for each question, then see if your instincts were right.
Cones! Your retina is packed with two types of cells: rods and cones. Cones need bright light to work and are responsible for letting you see thousands of different colours.
The amount of melanin in the iris. People with brown eyes have a lot of melanin, while people with blue eyes have very little. The iris is the part that regulates how much light enters your eye!
It changes its shape and thickness. It squeezes and stretches by about a tenth of a millimetre to shift focus from the end of your nose to 20 miles away!
Understanding the Science
Tap each card to reveal how the different parts of your eye work together to let you see the world.
Key Concepts
The Iris
Tap to learn moreThis is the coloured part of your eye. It controls how much light enters by changing the size of the pupil, acting like the shutters on a window.
The Lens
Tap to learn moreSitting right behind the iris, this clear part changes shape and bends light to focus an image exactly onto the back of your eye.
The Retina
Tap to learn moreThis is the back surface of the eye where the focused image lands (upside down!). It is covered in special light-sensitive cells.
Rods
Tap to learn moreThese cells on the retina are amazing at seeing in low light and only see in shades of grey. They give us our night vision.
Cones
Tap to learn moreThese cells need bright light to work and let us see the world in full, vibrant colour. They help us identify thousands of different shades.
The Optic Nerve
Tap to learn moreThis is the thick bundle of nerves that carries the image signals from the eye directly to the brain, like a high-speed data cable.
Tear Ducts
Tap to learn moreTears are constantly washing your eyes to keep them clean and moist. They drain out through tiny holes in the corner of your eye directly into your nose!
Ocularist
Tap to learn moreAn ocularist is a specially trained professional who makes artificial eyes. As we saw in the episode, they use both science and art to create eyes that look incredibly realistic, carefully matching the colour of the iris and even using fine nylon threads for veins!
Try It: Color Vision
Explore how the brain perceives colour when different wavelengths of light enter the eye.
Apply Your Knowledge
Now let us see if you can connect what you have learned to the real world.
Match the Eye Parts
Click an object to select it, then click the matching description to place it.
Real-World Challenge
Imagine you are walking into a dark cinema from the bright, sunny outdoors. Based on what you have learned, explain what happens to your iris, your rods, and your cones during the first few minutes you are in the dark room.
What Has Changed Since This Episode Aired
This episode of Bill Nye the Science Guy first aired in 1994. While the core anatomy of the eye remains perfectly accurate, here are a few things that have been refined or expanded through modern technology.
Updated: Scientists are making incredible breakthroughs! Researchers successfully used gene therapy to cure red-green colour blindness in adult monkeys in 2009. Progress and human trials are actively ongoing today, so watch this space for future treatments!
Updated: While hand-painting is still an incredible art form used today, some modern ocularists also use 3D printing and digital imaging to perfectly replicate the exact blood vessel patterns and iris details of a patient's other eye.
Updated: Today, we squint at screens constantly! We now know a lot more about "digital eye strain." Staring at screens for hours makes us blink significantly less, leading to dry eyes and blurry vision. The modern "20-20-20 rule" (looking at something 20 feet away for 20 seconds every 20 minutes) was developed to combat this!
Updated: Scientists have actually developed early "bionic eyes" (retinal implants)! These devices use external cameras on glasses to send electrical signals directly to the optic nerve, allowing some blind patients to perceive shapes and movement.
Test Your Understanding
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Results
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Reflection
Bill Nye the Science Guy mentions that many scientists consider the eyes to be an actual part of the brain. Based on how they work together to process images and flip them right-side up, why does this make sense to you?
Episode Discussion
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