How Do Eyes Work – Structure and Step-By-Step Function

by | Apr 2, 2020 | Anatomy | 0 comments

How Do Eyes Work Step By Step

How Do Eyes Work?

Different types of eyes are found in nature, and humans have eyes that are called “camera type eyes”. There is a structure in the eye that is called cornea, and it focuses light similar to a camera lens, projecting it onto a photosensitive membrane – the retina.

Eye Structure

The Cornea is a transparent plate in front of the eye that focuses light rays. Behind the pupil is a colorless, transparent structure – lens.  It fills the cavity between cornea and iris with transparent liquid.

Cornea is focusing most of the light, but further light rays go through the lens, that focuses it even more. 

Behind the cornea is an iris – colored annular membrane. Iris has a flexible, round opening, that is called a pupil. Pupil can constrict or dilate, controlling the amount of light entering the eye. Eye lens is surrounded by ciliary muscle – it keeps lens in place, and it has an important role in visual functioning.

When relaxed, muscle tightens and straightens the lens, making us able to see distant objects, however to see close objects, it has to constrict, to thicken the lens. There is a vitreous body inside the eyeball that is filled with gel-like liquid – Vitreous liquid.

Light rays passing through the lens still must pass through this layer, that is called Retina.

The Retina

Retina is deepest of three tissue layers, which together form the eye. The sclera forms the outer layer – it is what gives eyeball the white color.

Middle layer between the retina and sclera is called choroid, and it is part of the vascular lining that comprises ciliary muscle and iris.

Capillaries are located in choroid that provides retinal nourishment, supplying it with nutrients and oxygen, while discharging the waste. 

There are millions of light-sensitive cells in the retinasticks and cobs. 

Sticks handle monochrome vision in poor lighting, however cobs are needed to see colors and see details.

It concentrates cobs in the eye’s part just behind the retina, that is called retinal central cavity. 

Whenever sticks or cobs are touched by the light, it turns into electrical impulse, which enters the brain through the optic nerve, but in the brain converts electrical impulses into an image, in which We can see.

Iris

The Iris is ring-shaped membrane behind the cornea with an adjustable circular opening in the center called pupil. This part of them provides color for the eye.

Iris regulates light amount that gets into the eye. Muscular iris moves to shrink the pupil if there is too much light. Widen if there’s not enough light.

The brain controls all this function. It makes iris of connective tissue and smooth muscle fibers.

Change in color of the iris rarely happens. However, color of the eye might change. However, this is because of lighting changes based on nearby colors.

The Pupil

Pupil is the opening in center of the iris. Pupil functions to allow light to enter the eye so it could be focussed in the retina to process the light. Usually, pupils appear to be round and black.

The black color is because of light that passes through the pupil is absorbed by the retina and doesn’t get reflected.

If the lens has lost its black color and became pale, it is most likely because of formations of cataract.  When the lens is replaced by a clear intraocular lens during surgery of cataract, the normal appearance of the lens is restored.

How Does Pupil Function?

Together pupil and iris controls how much light can enter our eyes. The size of the pupil is controlled by the muscles withing the iris. One muscle constricts the pupil, other dilates it.

This process of muscle action represents how much light enters eyes. In conditions where is bad lightning pupil dilates more light so much that it can improve night vision.

However, in bright conditions, pupil constricts to limit how much light can enter the eye. (too much light can damage retina and the pupil).

Cornea

The cornea is eyes outer protective layer. Alongside with the sclera it protects eye from damage – dirt, germs and other things. Cornea has a very important role in vision.

After light enters the eye, cornea reflects or bends the light. This process helps to determine how well can eye focus objects that are close or far away. If cornea is damaged, it can affect your vision. Light can get distorted as it enters the eye.

Structure

1. Epithelium

This is first and outermost layer. Stops foreign objects from entering the eye. It absorbs nutrients and oxygen from the tears.

2. Stroma

The thickest layer that lies behind the epithelium. It is elastic but solid, because it is made of water and proteins.

3. Endothelium

Single layer of cells that’s behind the stroma. Clear fluid at the front of the eye is in constant contact with this layer. Stroma absorbs excess fluids and endothelium pulls it out. If the endothelium wouldn’t function as it is the stroma would become waterlogged. Therefore, vision would become hazy.

Sclera

The sclera is the dense connective tissue of the eyeball. Also called the white part of the eye that surrounds the cornea. Sclera itself doesn’t have any blood vessels.

Function

It’s function alongside with the intraocular pressure of the eye is to maintain shape of the eyeball. Sclera also protects eye from serious damage like rupture or laceration. Also, it provides sturdy attachment for the extraocular muscles that control the movement of the eyes.

What happens if sclera is damaged?

If sclera is damaged, then inflammation begins in one area and then spreads until the sclera gets involved. Depending on the damage, it can damage vision or cause entire loss of the vision.

Most common complications are: keratitis (inflammation), uveitis, cataract, glaucoma.

Can Scleritis Be Cured?

It depends on the severity. Sometimes steroid drugs might help. Antibiotics for infection and medicine for immune system problems. With right treatment, it can go away in few weeks.

How Do Your Eyes Work?

Eyes work in step by step process. 

  1. Light enters the cornea and then into pupil.
  2. Then the light goes through a lens and then into the retina.
  3. Retina reads it and sends the signal to the brain

How Do We See Things?

We can see things thanks to cornea, the pupil and the retina. These parts of the eye works together to focus light. Then this signal is sent to the brain, and it can understand.

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