Important Notes on Human Eye

By Naveen Singh|Updated : June 25th, 2020

The human eye is one of the most sensitive sensory organs of sight that allows us to see the marvellous world of light and colour around us. It is like a camera with a la lens system that forms an inverted, real image inside the eye on a light-sensitive screen.

It's a spherical ball in the front portion with a tiny bulge covered by scleroid and choroid. It's in the socket of the eye. 

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Structure:

Cornea

It is the transparent spherical membrane that covers the eye's front. It is the white component of the eye that enables the entrance of light serving the sight of the world through a window.

Aqueous Humor

It is clear area of liquid between the lens and the cornea. its role is to safeguard the eye's outer portion from collapse when the atmospheric pressure changes suddenly. Also, when we wink our eyes, it is the fluid that flows out of the eye. So, it washes the eye, keeping it moist as well.

Iris

It's part of the eye in colour. It holds the pupil and adjusts the pupil's size to the light intensity.

Lens

It is a clear, material-like lens made of jelly with a convex lens-like cellular structure (diverging lens).

Ciliary fibres

They're holding the lens and change the lens' focal length.

Pupil

It absorbs all the rays of light that fall on it. Depending on the intensity of light it gets constricted or expanded

Vitreous Humor

It fills the room between the eye lens and the retina. It is a thick jelly-like fluid in the back of the eye and its role is to safeguard the back of the eye from collapse when the atmospheric pressure changes suddenly. It also helps to focus the picture clearly on the retina.

Fovea

Small pit in the retina macula providing the clearest vision of all. The layers of the retina spread beyond the fovea alone to let light fall straight on the cones, the cells that offer the sharpest picture. Also known as the central fovea or fovea cntralis.

Retina

It's an eye's back surface acting an eye screen where a picture is created.

It comprises of two cell kinds:

-        Cone cells: cells that react to colors.

-        Rod cells: cells that react to light intensity.

-        Yellow spot: A point where the clearest picture is created on the retina.

-        Blind place: This is where no picture is created on the retina.

Disc

For ganglion cell axons leaving the eye, the optical disk or optic nerve head is the exit point. Because the optic disk does not have any rods or cones, it corresponds to a small blind spot in each eye.

 

After leaving the eye, the ganglion cell axons form the optic nerve. The optic disk is the start of the optic nerve and the point where retinal ganglion cells axons come together.

Sclera

The sclera, also known as the eye's white, is the human eye's opaque, fibrous, protective, outer layer that mainly contains collagen and some elastic fiber.

Optic Nerve

An eye-connecting nerve with the brain.

Choroid

It is a grey membrane from the inside connected to the choroid. Its role is to obscure the inside of the eye so that there is no internal reflection.

Scleroid

It is the ultimate covering made up of white fibers and its function is to safeguard all sections of the eye.

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Eye Defects

Myopia

It is a defect in which a person cannot see distant objects but can see objects nearby. The reason is that the ciliary muscles do not relax correctly, because of which the focal length does not raise correctly, the lens does not elongate correctly. No clear picture is created as a consequence.

Solution: To correct a short-sighted vision, a suitable focal lens (concave lens) is placed in front of the eyes. The concave lens diverges the rays of light from a remote object so that the final picture is created at the retina. 

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Hypermetropia

It is a defect in which a person cannot see objects nearby but has a comfortable sight for objects far away. The reason is that the ciliary muscles do not contract correctly, because of which the focal length does not reduce, the lens does not become dense and short. As a result, the formed image is not clear and the brain cannot identify it.

Solution: A far-sighted individual has the ordinary distance but requires a converging lens to concentrate items as near as 25 cm. The converging lens of the right focal length will create the virtual image at the real near point of the eye of the farsighted person.

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Presbyopia

It occurs as age increases gradually. Like other muscles, our ciliary muscles weaken, i.e. they cannot correctly contract or relax. As a result, a person cannot obviously see items close or far away. Using spectacles containing a bifocal lens, correction can be performed.

Vision

Persistence of Vision:

When the object is removed from sight, the image formed on the eye's retina does not fade away instantly. The object's feeling (or feeling) continues on the retina for about a second (1/16) even after removing the object from sight. This continuation of eye feeling is called sight persistence.

Power of Accommodation:

By altering the focal length of the eye-lens, which is comprised of fibrous jelly-like material, the ciliary muscles can modify the picture of objects at separate distances from the eye to concentrate on the retina.

Near and Far point

The closest point where the eye can clearly see a tiny object is called the near point. It is about 25 cm for an ordinary eye and is marked by the symbol D.

The strength of the eye's lens declines with the advancing era in the eye lens gradually loses its flexibility. The near point is about 200 cm for most older people aged nearly 60 years, and corrective glasses are required to obviously see neighbouring items.

The farthest point to which our eye can obviously see objects is called the far point without any pressure on the eye. The distance point is at infinity for an individual with normal vision.

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