Human Eye

The eye is a very important sense organ of each animal. By this, all organisms see in their environment. The human eye is a paired sense organ that reacts to light and allows vision.

Structure of Human Eye

human eye

There are 11 main parts of the human eye which are mentioned below-

The sclerotic

The human eye is like a hollow ball that is covered with a firm and opaque white layer from the outside. This opaque layer is called sclerotic which provides protection to the inner parts of the human eye.


It is a black-colored membrane lying inward from the inner part of the sclerotic that absorbs light and prevents internal reflection. The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye, containing connective tissues, and lying between the retina and the sclera.


It is some embossed transparent part of the front of the eye that allows light to enter the eye and most of the refraction of the rays of light is on the outer surface of the cornea. The horizontal diameter of the cornea typically measures about 12 millimeters (mm), and the vertical diameter is 11 mm when viewed from the front. 


It is a colored opaque membrane curtain behind the cornea and acts as a diaphragm of the camera. The iris is usually strongly pigmented, with the color typically ranging between brown, hazel, green, gray, and blue. So the color of the eye depends on the color of the iris.


It is a hole in the middle of the iris that controls the amount of light entering the eye. When the light is bright, the iris shrinks and makes the pupil smaller, allowing a limited amount of light to enter the eye, and when When the amount of light is less, then the iris spreads and makes the pupil larger so that more light can enter the eye.

Eye Lens

Just behind the iris is a transparent and soft convex lens made of a protein called an eye lens. The curvature radius of the rear of the lens is smaller and the curvature radius of the next part is larger. The refractive index of the substance of the lens is about 1.44.

Structure of human eye

 The Retina of the Human Eye

It is a curtain made of optic nerves located in the innermost part of the eye which is connected to the brain by nerve cells from the backside. There are two types of light-sensing cells cone-shaped and rod-shaped on this screen, which provide knowledge of the color and intensity of light, respectively. The eye lens makes its inverted reflection on the retina itself by rays of light coming from an object.

Ciliary Muscles

The ciliary rests in its place with the help of the muscles. As a result of these stretches and dysfunction, the focus distance of the eye lens increases and decreases respectively.

Aqueous and Vitreous Humor

The saline transparent substance between the cornea and the eye lens is called aqueous humor and the transparent fluid between the retina and the lens is called the vitreous humor. The refractive index of aqueous or vitreous humor is equal to the refractive index of water. The aqueous chamber between the cornea and the eye lens and the part between the eye lens and the retina is called the vitreous chamber.

Yellow Spot

It is a round yellow dot near the center of the retina. At this point, the sensitivity of light is highest so that the reflections formed on this day are most visible.

Blind Spot

The point of the retina from which the visual nerves go to the brain is called a blind spot. There are no cone-shaped and rod-shaped cells at this point, so the reflection formed at this point is not visible. 

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