Human eyes

WHAT IS HUMAN EYE

If I ask you what is an eye you will say it is an organ through which we see, which is absolutely correct but do you know anything more about it?
I don't think so , someone has said right , "We dont care for what we have"
Let us get to know something more about our own eyes.
Our eye is the only extension of the brain which we can see from outside , isn't it amazing!?
Let us have a look on the structure of the eye . Here's given a diagram of a human eye.

Human eye

STRUCTURE

The adult human eye is nearly spherical in shape. The wall of the eyeball comprises of three layers. The outermost layer is sclera/fibrous tunic, middle layer called vascular tunic ( choroid , ciliary body , iris ) and third which is the innermost layer is called retina . Retina is made of light sensitivity cells.

COMPONENTS

•  Sclera : Sclera is a milky white layer which also forms cornea which is transparent.

•  Cornea : It is curved surface which helps in refraction of light entering the eye . Lacrimal glands(tear glands) helps cornea keeping itself moist and dust free.

• Choroid : it is bluish in colour and not visible from outside as it is covered by sclera. This helps in preventing the reflection of light rays within the eyes.

• Ciliary body : Choroid layer becomes thick in the anterior part and forms ciliary body. It continues forward to form an opaque and pigmented(coloured) structure called iris.

• Iris :  The coloured portion of the eye. Blue , Black , green , blue ,etc all the beautiful colour diversity of the eyes from different countries are responsible because of iris.

• Pupil : The opening/aperture between the iris is called pupil. It protects the eyes from entering more of light or we can say regulates the amount of light entering the eye which helps in protecting the interior as well as giving a sharp image. This regulation is done by changing pupil's size by muscle fibres of iris called iridial muscle.

•  Retina : The inner layer of eyeball made of photo receptor cells , rods and cones.

• Aqueous and Vitreous Chamber : The anterior chamber present between the cornea and the lens is called aqueous chamber . This chamber is filled with a watery fluid called as aqueous humour which helps in nourishing the lens.The posterior chamber is present between the lens and the retina and is called vitreous chamber. Vitreous chamber is filled with gelatinous hard liquid material called the Vitreous humor which helps in supporting the eyeball.Both humors also help in maintaining pressure in the eye.

FUNCTIONING

Human eye is just like a camera. The lens focuses the light rays coming from outside onto light sensitive cells of retina. Light rays need to be bent or refracted to focus on retina and this refraction is done by curved cornea, eye lens and aqueous and vitreous humors.
The light falls on rods and cones(photoreceptor cells of retina) which causes dissociation of retina from opsin(eye protein) which changes the structure of opsin which further changes membrane permeability which helps in exchange of some ions which ultimately results in potential differences in rods and cones and some signals are generated. These signals/impulses are transmitted to optic nerve and the to visual cortex of the brain.
Impulses after reaching the visual cortex are analysed and image formed on retina is recognized. The image formed on retina is inverted but when the Impulses are transmitted to brain ,it converts the image and therefore we see correct images.