What shape are our eyes? What are they made of? How do they work? What’s the point of having two eyes if we only see one image? Why do we blink? What’s the point of tears and why are they salty? We answer your questions about eyes in the first of two episodes with Dr. Sujata Singh, a pediatric ophthalmologist at the University of Vermont Medical Center.
Download our learning guides: PDF | Google Slide | Transcript
- Eyes are made of specialized tissues. They’re complicated and delicate. Your eyes include blood vessels, a mucus membrane, nerve tissue, light receptors, muscles and a see-through jelly-like substance that fills a lot of the inside of your eyeball called the vitreous humor!
- Eyes are kind of ball shaped, but not exactly. The lens of your eye is curved like a second smaller ball. Dr. Singh describes them like a big ball and a little ball kind of stacked and smushed together.
- If you could touch your eye it’s not hard like a marble or soft like a marshmallow. It’s maybe more like a firm grape.
- There are many specialized parts of the eye. The pupil, the retina, the lens, and the cornea are just a few.
- Eyes are complex optical devices and the way we see is also complex. Light enters our eye through our cornea. Our pupils (the dark part of the eye) can expand or adjust to let the right amount of light in. In bright light, pupils will be smaller. In darker conditions, the pupil opens up to let lots of light in. The lens of the eye focuses the light onto our retina. The retina then sends the image to the optic nerve, which sends the information on to the brain.
- We have binocular vision, meaning we see with two eyes, not that we’re using binoculars. Each eye sees the same thing, but from a slightly different angle. Your brain learns to combine what the two eyes see, giving you a sense of depth, 3D vision. (Many people get along just fine with one working eye though.)
- If you want to test out how something can look slightly different with each eye, hold up a finger in front of your face, but don’t focus on your finger–focus on something back behind it. Close one eye and then the other, and see how your finger appears to move, relative to the background.
- Blinking helps provide moisture and nutrients to your eyeball by helping to spread tears across your eye. Those are called basal tears. We blink involuntarily, but we can also control our blinking.
- Sometimes we make more tears if there’s something irritating one of our eyes, to flush it out. Those are called reflex tears.
- Tears contain water, electrolytes (salts), oil and proteins. They’re salty because all of our bodily fluids are a little bit salty.
- Our bodies also make a third type of tear: emotional tears, when you cry out of happiness, sadness, frustration or fear.
- Your tears drain into ducts at the base of your eyes, and into your nose. (Unless they overflow and fall down your cheeks.) That’s why you sometimes get a stuffy nose when you’ve been crying.
