Inside the Eye I How to see your Eye Blood Vessels?!

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I for Inside the Eye

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Background image credit: Dr. Robert Berdan (

The only way out to see something from inside your body is by doing an x-ray or ultrasound. But, here’s one cool, mind-blowing science activity to see your blood vessels inside the eye!

Tips to introduce this activity to children

  • It’s not common that children are introduced to the science of the human body at home except for organs like stomach, heart or brain. Perhaps, children get to understand that food goes to the stomach, gets digested, and comes out. Perhaps, they know blood because they would have seen it at some point. But in reality, everything about the human body is obscure for them because they don’t see it.
  • Now if they have a fair knowledge of what we call blood and that it runs throughout the body within pipes called blood vessels, they might be interested to see their own blood vessels.
  • Alright, but can we, really? Yeah, seeing blood vessels inside the eye is possible!

Things you’ll need

A penlight or flashlight (preferably something that projects a thin beam)

Dark room

Safety goggles (recommended)

How do you do it?

1. Get inside a dark room. Wear your goggles, though it is just okay if you don’t use one.

2. Close one eye with one of your palms.

3. Hold a flashlight just under your open eye (if done right, the light shouldn’t be directly entering your eyes). Caution: a strong light projected directly into your eyes in a dark room can be harmful or cause pain in the eye. Make sure the light projection feels comfortable to your eyes while you try this out.

4. Now, slowly move the flash light to either sides and see what you see!

So, What would you see?

You will observe a pattern in black against a greyish background that looks something like a river branching out into streams or a root of a plant branching out sideways. What you are actually seeing is the shadow of the blood vessels inside the eye.

The Science behind

How do we get a shadow? When a non-transparent object obstructs the path of light, light cannot pass through it, but can pass along the edges/sides of the object and forms its shadow on the other side. So, what does it got to do here?

retina photograph of right eye
Retina photograph of a right eye – Image credit: Dr. Robert Berdan

What we see as our eyes in the mirror is the open end of the eyes. And there’s another end to the eyes within our eye balls what we call the retina. That is, the retina of our eye is located at the back-most part of our eye. It acts like a screen that receives the input from outside our eyes and communicates with our brain to show us what’s in front of us.

Now imagine that the blood vessels that supply blood to the retina are located in between the retina and the open end of our eye (well, that’s how it is really). In our activity, the thin beam of light enters our eyes, passes along the edges of the blood vessels and casts the shadow of the blood vessels on to the retina. And that’s exactly what we see – the shadow of the blood vessels inside the eyes.

An interesting question for you – Why then don’t we see the shadow of the blood vessels all the time? 

That’s because the retina can detect only images that are in motion. And know that there is always a slight vibration inside the eyes which causes a constant motion for the retinal capture. You can sense this constant vibration by trying to focus your vision on one particular point. You’ll find it difficult to do it because of the constant movement inside the eye.

So, relative to the images outside the eye, the blood vessels are not moving and hence the retina does not project the shadow of the blood vessels into your vision all the time. But, in this activity, making the light source move slightly, causes the shadow of the blood vessels to move and that’s why we see it.

Share your experience

Did you try? Did it work? Did you see your blood vessels inside the eye? Leave a word in the comment section. I would love to hear!

Here’s the full list of DIY Science Experiments in this series:

A for Air – Does Air has Weight?

B for Buoyancy – Can Egg float on Salt Water?

C for Capillary action – Rainbow Walking

D for Density – 3 Layer Density Experiment

E for Earth & Moon – Why does the Moon change its shape?: Phases of the Moon

F for Fire – Does Fire need Oxygen to Burn?

G for Gravity – Defying Gravity

Inside the Eye – How to see your Eye Blood Vessels?!

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