The Eye

Keywords

Rods, cones, accommodation, hyperopia, myopia, eye, sight, looking, iris, pupil, cornea, sclera, macula, optic nerve, retina.

Introduction

We all need to be able to see, right? So, what do we use? Our eyes. They are the windows to the world for us, and we need to be able to understand them, as well as look after them. So, how do they work?

A Little Closer

The eye is a circular (and sometimes oval) ball in our skulls that allow us to see. We base a camera on the same function as the eye. A camera has a moving focal point, which enables the camera to see things up close, as well as far away. Our eyes work in a similar fashion to this.

We can sometimes have conditions or instances where we cannot see properly, and for this, we have treatments in the forms of glasses, contact lenses and corrective laser surgery to fix these issues.

Interesting fact: the eye hs 256 unique characteristics. This is better than a fingerprint, which has around 40, and hence why retina scans are more and more popular.

Hyperopia vs Myopia

We know these two terms as long sighted and short sighted. But what does that actually mean?

When you're long sighted (hyperopia), you will be able to see things easily that are very far away, but not very well close up.

When you're short sighted (myopia), you will be able to see things easily that are very near, but not very well that are far away.

To correct both of these issues, you can do one of a few things:

Inside the Eye

There are several parts to the eye that enable us to see properly. If you look at a diagram of the eye, you will see the following parts:

Cornea

The very front of the eye that we see, the cornea, is a dome shaped tissue that covers the eye. In theory, you can touch this part, but I wouldn't recommend it. Being at the very front of the eye and being open to the air, it can be irritated by dust or other substances. This is where blinking comes in to remove those substances.

Iris

The iris is the part of the eye that changes colour as you grow older. When we are all born, we are born with blue eyes, but depending on the dominant genes in your DNA, this can change. They can be green, brown, grey or a mixture of the three in any form.

Pupil

The pupil is where the light intensity comes through to the back of the eye. It doesn't have any access to a blood vessel, so it takes its supply of oxygen from the air itself. If the pupil did have a blood vessel go across it, we would see things with a red tint or glow all the time. The pupil changes in size depending on the amount of light in the area, much like the aperture of a camera.

Lens

The lens enables us to help focus on an object. More precisely, it allows your eye to focus the amount of light that hits the retina. This then allows the signals to go to the brain with the image we see.

Retina

The retina is at the back of the eye. This contains photoreceptors (like the negative of an old camera), which are upside down. That's right, the images we see that are the correct way up, are actually seen upside down at first by the brain. The brain processes them to make them the right way up.

Rods & Cones

Rods and cones in your eye, more specifically in the retina, are tiny cells that are known as photoreceptors. They allow your brain to see colours, and the amount of light that enters the eye.

Cones are conical in shape, and are made of a protein called photopsin. There are three types of cone, each receptive of a certain colour. Like your television at home, which has a range of colours to be visible using the LED or LCD screen. Your eyes also work in similar fashion.

The cones are separated into the three colours - blue (10%), red (60%) and green (30%). They are responsible for central vision.

Rods are cylindrical in shape, and are also made of a protein, this time called rhodopsin. This allows you to see things in lower light intensity (when it's dusk for example). Although they allow us to see in the darker moments of the day, they do not allow for colour, so often we find it difficult to see in the dark.

Optic Nerve

Situated at the back of the eye, the optic nerve sends the signal from the eye of the image that we see back to the brain for processing. Once processed, this is then flipped back the right way round, and sent back to the eye to give us our sight and vision. It is lightning quick, as it is pure electrical signalling.

Macula

Also situated at the back of the eye, the macula provides us with clear vision. For example, take a projector and a screen. The screen needs to be a certain distance from the projector in order for it to be focal (sharp sighted) and enable us to see clearly. This is what the macula does to enable us to see clearly. It can be given a different focal position (like when we 'stare into space' for example), as your gaze can be changed.

Conjunctiva

The conjunctiva is located at the front of the eye, above and below the cornea, and is simply a membrane that helps protect the eye. It links to the eyelids so you can close them and open them properly, and is situated on top of the sclera.

Sclera

The sclera is the part of the eye that is known as the whites. This is the part we see in the mirror everyday when we look at them, and they are usually white in colour. We can get conditions that change their colour, such as conjunctivitis (pink-eye), and can get inflamed.

On the inside, the sclera is not white, it is brown, and has grooves in it, which attaches to the tendons of the eye.

Aqueous & Vitreous Humour

No, it's not funny. Honestly. What it is is a fluid susbtance that fills the eye. It's split into two chambers: one is at the front of the eye, called the anterior chamber. This allows movement of the iris and pupil, and the posterior chamber is at the back in the main 'bulk' of the eye.

This area is also known as the vitreous humour. It helps to maintain the shape of the eye, and gives your vision clarity. It can also absorb a shock to the head, so if for instance, you were to hit a football with your head, it would resonate into the eye and be absorbed. It's like a failsafe system for the head.

Rods & Cones

Rods and cones in your eye, more specifically in the retina, are tiny cells that are known as photoreceptors. They allow your brain to see colours, and the amount of light that enters the eye.

Cones are conical in shape, and are made of a protein called photopsin. There are three types of cone, each receptive of a certain colour. Like your television at home, which has a range of colours to be visible using the LED or LCD screen. Your eyes also work in similar fashion.

The cones are separated into the three colours - blue (10%), red (60%) and green (30%). They are responsible for central vision.

Rods are cylindrical in shape, and are also made of a protein, this time called rhodopsin. This allows you to see things in lower light intensity (when it's dusk for example). Although they allow us to see in the darker moments of the day, they do not allow for colour, so often we find it difficult to see in the dark.