The human eye is a specialized sensory organ that allows us to see things.
It is roughly round in shape and sits in a protective bony socket known as the orbit.
The eye is attached to the orbit by six extraocular muscles.
These muscles allow the eye to move in all direction.
Human Eye is further protected by eyelids from external environment.
Now Lets take a closer look at detailed structures of the eyeball.
The human eye is made up of three Layers: 1. Outermost Layer –
2. Middle Layer – 3. And the Innermost Layer –
Outermost Layer is composed of the cornea and the sclera.
Sclera is the white visible portion of the eyeball.
It is a tougher layer of tissue than the delicate internal structures of the eyeball.
The extraocular muscles that move the eyeball are attached to the sclera.
From the front of the eye, the sclera becomes transparent and moves upward,
forming a dome-shaped structure known as the cornea.
The cornea is the first optical component of the eye machinery.
Light enters the eye through the cornea and focused.
In fact, the cornea provides 70% of the eye's focusing power.
Behind the cornea is a fluid-filled space called the anterior chamber.
The fluid inside the anterior chamber is called aqueous humor,
which helps in maintaining constant eye pressure.
Cornea and sclera also act as a barrier against dirt,
germs, and other substances that can harm the eye.
The Middle Layer
The Middle layer of eye is composed of the choroid, ciliary body, lens and iris.
The choroid is a thin, blood-rich membrane that lies beneath the sclera,
and is responsible for supplying blood to the eye, especially to the retina.
The central portion of the front of the eyeball is termed as iris.
Iris is a circular shaped, pigmented structure.
And the different colors we see of the eyes are due to iris pigmentation.
At The center of Iris a dark colored opening is present called pupil.
Iris allows light to pass through it, onto the lens.
It helps regulate the amount of light entering the eye.
It acts just like aperture of camera, when there is a lot of light,
the iris constricts the pupil, allowing less light to pass through.
And when there is a lack of light, the iris dilates the pupil to allow more light in.
This is why we can't see anything for a few
moments when we go from bright sunlight to a dark interior.
And this is also the reason that we can't keep our eyes
open when we turn on the lights in the middle of the night.
The next structure in the middle layer of eye is the Lens.
The lens is a transparent structure that is located directly behind the pupil.
Lens is responsible for correct focusing of the visuals on to the light sensitive layer Retina.
Our Eye lens is flexible in nature,
and adjusts according to the external lighting with the help of ciliary bodies.
In between the lens and ciliary body Suspensory ligaments are present that
connects the ciliary body and the lens, and facilitates the adjustment of lens.
By focusing the light, the cornea and the lens both play
important roles in giving us a clear vision.
The Innermost Layer – The innermost layer of the eyeball is retina.
Retina can be imagined as the wall on which the images are projected.
The light passing through cornea, pupil, and lens gets focused on the retinal membrane.
Retina is made up of two types of cells: rod cells and cone cells
(These cells are also called photoreceptors).
These cells are responsible for converting the
light that enters your eye into electrical signals,
and then these Electrical signals transferred to the brain through Optic nerve for visualization.
Inside these three layers, there is a vitreous cavity
lies between the lens and the back of the eye.
A jellylike transparent fluid called vitreous humor fills the cavity.
Vitreous humor plays an important role in maintaining the round shape of the eye.
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