Human eye

As we know that eyes play a very crucial role in our life. The human eye is the most valuable and sensitive part of the human body. It helps us to identify the different colours. There is no doubt that by closing our eyes, we can identify the objects around us to some extent only because of their smell, texture, smell, or sound which they make. But it is impossible to identify the colour without an eye. Thus, the human eye is one of the most significant organs, as it enables us to see the beautiful world around us. As we know, the human eye has a lens. Now in this article, we are going to study in detail how images form in our eye, how the eye helps us to identify the colour, how lenses fit in our eye, how they function in our eye etc.

The human eye is just like a camera. Here we discuss how it functions for the formation of images in our eyes.

The eye has an outermost layer named cornea; it is a very thin membrane. On the front surface of the eyeball, a transparent bulge forms. The white part is a watery fluid called sclera. Behind the cornea, a small muscular diaphragm named Iris. The eyeball is filled with liquid called vitreous humour which is present between the lens and the retina. Retina contains 125 million receptors called ‘rods’ and ‘cones’ and there is a region where the optic nerve enters called ‘blind spot’. There is another spot called the ‘yellow spot’ also named as macula lutea, which is the central part of the retina. There is a crystalline structure called the lens. Behind the cornea, there is a liquid called ‘aqueous humour’. The iris is present between the aqueous humour and the lens. The iris has a small pore called pupil. The eye lens is hard in the middle and soft toward the edge, also the lens consists of fibrous, jelly-like material and also the lens is attached by the ciliary muscles. The outermost covering of the eye is of white fibrous tissue called Sclera or Sclerotic. The ‘choroid’ is another membrane which is attached to sclera.

FUNCTION OF EYE

How eye functions in our body,

The human eye is a complex organ, as it performs its function by its different parts. Here we discuss the parts of the human eye that work differently and what is the function of each part. The eye consists of the eyelids which cover the eye and provide protection. The eyeball consists of a small spherical shape that is approximately 2.3cm in diameter.

Let’s consider the steps to understand the image formation of an eye well.

Step 1)  Lights enter the eye through a thin membrane called the cornea.

Step 2) After falling onto the cornea, it then passes through the aqueous humour.

Step 3) Next, it passes through the lens and then vitreous humour.

Step 4) Here, the final image is formed on the retina.

So, if the final image formed on the retina is not correctly accomplished then the viewer may suffer from the diseases called nearsightedness and farsightedness. But this is not a severe problem, as both these conditions can be corrected by the optical lenses.

The retina has complex photoreceptors called rods and cones. When these photoreceptors come in contact with light, they produce electrical signals. These electrical signals are then transmitted to the optic nerve in the brain.

In the region where the optic nerve enters into the retina, there are no photoreceptors. This point is called ‘blind point’. And if the light falls on the blind spot, the image will not be visible to the viewer.

The other important fact is, the rods and cones did not have continuous links; rather, they were linked by three distinct layers of cells. This connection or junction is called ‘synapses’. Rods and cones are connected by the layers of the cell to the ganglion cell. So, the light enters into the various cell layers and is then transmitted to the various synaptic junction. Furthermore, there is a small structure of receptive fields with the excitatory lobe to one side and the inhibitory lobe to another side. It is an antisymmetric field. This even and odd arrangement of receptive fields are known as simple cells. Other types of receptive fields are known as complex cells which are found in the retina. They perform more complex functions.

Parts of human eye and their functions,

CORNEA – It is a thin membrane where light starts its journey. This transparent layer is the outermost layer which is present on the top of the iris. And also it acts as a protective layer.

Crystalline lens –  This lens provides fine adjustment of the focal length required to focus the object at different distances on the retina. This eye lens is a double convex lens that helps to form the final inverted real image on the retina.

IRIS – Behind the cornea, the iris is present which controls the size of the pupil. It is a dark muscular diaphragm. It also acts as the shutter of the camera.

PUPIL – There is a small pore present on the iris through which the light enters and falls on the lens. The pupil regulates and controls the amount of light entering the eye.

CILIARY MUSCLES – Ciliary muscles help to change the focal length of the eye lens.

AQUEOUS HUMOUR – The space between the cornea and eye lens is filled with the transparent fluid called aqueous humour.

VITREOUS HUMOUR – It is the space between the eye lens and retina that is filled with jelly-like structures.

RETINA – Retina serves as the platform for the formation of the final real image. It is present at the back of the eye lens. The retina is formed of light-sensitive cells, which are connected to the optic nerve.

OPTIC NERVE – The optic nerve carries the information to the brain and the region where the nerve enters on the surface of the cornea is called the blind spot.

BLIND SPOT- The region where the optic nerve enters is called a blind spot. If the image formed on the blind spot is not visible.  

Conclusion

Eyes are responsible for the vision, identifying the colour, objects. The structure of the eye can be broadly differentiated into internal and external structures. External structures include sclera, conjunctiva, cornea, iris, pupil whereas internal structures include retina, lens, aqueous humour, vitreous humour and optic nerve. The light ray directly falls on the surface of the cornea from where it then passes through the small pore called pupil present on the surface of the iris. After passing through the pupil, it falls on the eye lens, from where it forms a final image on the retina.