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11
0
Ly
09/12/2025
Biology
The eyes biology
262
•
9 Dec 2025
•
Understanding Eye Biology
Ly
@userly
1 / 4
Eye Structure and Function
Your eye is like a sophisticated camera with several key parts working together. The cornea acts as the first contact point for light - it's completely transparent because it has no blood vessels and gets oxygen by diffusion.
The lens sits behind the cornea and can change shape to focus light precisely on the back of your eye. Your iris (the coloured part) controls how much light enters by adjusting the pupil size, whilst the optic nerve sends visual information to your brain.
The retina at the back contains two types of light-sensitive cells. Cone cells detect colour but need good lighting to work properly. Rod cells are much more sensitive and work in dim light, but only show black and white images.
Quick Tip: The fovea is a special spot on your retina packed with cone cells - this is where you get your sharpest, most detailed vision.
Iris Reflex and Pupil Control
Your pupils automatically adjust to protect your retina from damage and help you see clearly in different lighting. This happens through two sets of muscles in your iris working like opposing teams.
In bright light, your pupil gets smaller (constricted). The circular muscles contract whilst the radial muscles relax, making the pupil tiny to prevent too much light from entering.
In dim light, your pupil widens (dilated) to let more light in. Now the radial muscles contract and pull outwards whilst the circular muscles relax.
This entire process happens automatically - you don't have to think about it! Your eye constantly monitors light levels and adjusts within seconds.
Remember: Bright light = small pupil, dim light = large pupil. It's your eye's built-in protection system.
Accommodation - Focusing Near and Far
Accommodation is how your eye changes focus between near and distant objects. When you look at something close (like your phone), you need strong light refraction, so your lens becomes short and fat.
This happens because the ciliary muscles contract, which makes the suspensory ligaments slacken. Without tension pulling on it, the lens naturally becomes more curved and powerful.
For distant objects, your cornea does most of the work refracting light. The lens barely needs to bend light, so it stays stretched and thin. The ciliary muscles relax, pulling the suspensory ligaments taut.
Key Point: Suspensory ligaments aren't muscles - they can't contract or relax, only slacken or get pulled tight by the ciliary muscles.
Vision Problems and Corrections
Long-sightedness (hyperopia) means you struggle to focus on nearby objects because your eye doesn't refract light strongly enough. The image would form behind your retina instead of on it.
Convex lenses in glasses solve this by adding extra refraction power, bending light inwards before it reaches your eye. This helps focus the image exactly on your fovea for clear vision.
Short-sightedness (myopia) is the opposite problem - your eye refracts too much light, forming images before they reach the retina. Distant objects appear blurry because the light rays cross too early.
Concave lenses fix this by spreading light rays outwards first, so when your eye refracts them, they focus perfectly on the retina instead of in front of it.
Easy Memory Trick: Long-sighted = convex lenses (curve outwards), short-sighted = concave lenses (curve inwards).
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Understanding Eye Biology
Ly
@userly
Ever wonder how your eyes actually work and why some people need glasses? Your eyes are incredible organs that automatically adjust to different lighting and distances throughout the day. Understanding how the eye's structure functions can help explain common vision... Show more
Eye Structure and Function
Your eye is like a sophisticated camera with several key parts working together. The cornea acts as the first contact point for light - it's completely transparent because it has no blood vessels and gets oxygen by diffusion.
The lens sits behind the cornea and can change shape to focus light precisely on the back of your eye. Your iris (the coloured part) controls how much light enters by adjusting the pupil size, whilst the optic nerve sends visual information to your brain.
The retina at the back contains two types of light-sensitive cells. Cone cells detect colour but need good lighting to work properly. Rod cells are much more sensitive and work in dim light, but only show black and white images.
Quick Tip: The fovea is a special spot on your retina packed with cone cells - this is where you get your sharpest, most detailed vision.
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Iris Reflex and Pupil Control
Your pupils automatically adjust to protect your retina from damage and help you see clearly in different lighting. This happens through two sets of muscles in your iris working like opposing teams.
In bright light, your pupil gets smaller (constricted). The circular muscles contract whilst the radial muscles relax, making the pupil tiny to prevent too much light from entering.
In dim light, your pupil widens (dilated) to let more light in. Now the radial muscles contract and pull outwards whilst the circular muscles relax.
This entire process happens automatically - you don't have to think about it! Your eye constantly monitors light levels and adjusts within seconds.
Remember: Bright light = small pupil, dim light = large pupil. It's your eye's built-in protection system.
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Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Accommodation - Focusing Near and Far
Accommodation is how your eye changes focus between near and distant objects. When you look at something close (like your phone), you need strong light refraction, so your lens becomes short and fat.
This happens because the ciliary muscles contract, which makes the suspensory ligaments slacken. Without tension pulling on it, the lens naturally becomes more curved and powerful.
For distant objects, your cornea does most of the work refracting light. The lens barely needs to bend light, so it stays stretched and thin. The ciliary muscles relax, pulling the suspensory ligaments taut.
Key Point: Suspensory ligaments aren't muscles - they can't contract or relax, only slacken or get pulled tight by the ciliary muscles.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Vision Problems and Corrections
Long-sightedness (hyperopia) means you struggle to focus on nearby objects because your eye doesn't refract light strongly enough. The image would form behind your retina instead of on it.
Convex lenses in glasses solve this by adding extra refraction power, bending light inwards before it reaches your eye. This helps focus the image exactly on your fovea for clear vision.
Short-sightedness (myopia) is the opposite problem - your eye refracts too much light, forming images before they reach the retina. Distant objects appear blurry because the light rays cross too early.
Concave lenses fix this by spreading light rays outwards first, so when your eye refracts them, they focus perfectly on the retina instead of in front of it.
Easy Memory Trick: Long-sighted = convex lenses (curve outwards), short-sighted = concave lenses (curve inwards).
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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Students love us — and so will you.
4.9/5
App Store
4.8/5
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user