Introduction

The human eye is around 2.3 cm in diameter and can be considered as a spherical ball containing fluid. It is one of the most developed and highly functional sense organs in our body. It not only helps in visualization but offers perception, colours and depth perception for far and near objects. It is fascinating to know about the anatomy, structure, and functioning of the different parts of the human eye.

What is the anatomy of the human eye?

The human eye is protected from any mechanical injury as it is enclosed in a socket or orbit. The orbit consists of multiple bones from the skull that form a four-sided pyramid. The apex of this pyramid points back to the head. Its floor is made up of the palatine bones and zygomatic bones. The roof of the orbit is made up of the orbital plate of the frontal bone. The lesser wing of the sphenoid lies behind the orbit’s roof.

The eyelids form the front surface of the human eye and are part of the eyeball. It keeps the cornea moist and eyes protected from dirt and impurities.

What are the different parts of the human eye?

There is a blind spot in the human eye which is located at the junction of the optic nerve and retina. There are no sensory nerve cells, and hence no vision is possible at the blind spot. The human eye is made up of the following parts:

Structure of the human eye

1. Sclera: The white part of the human eye is called the sclera. It is an important part of the human eye because it supports the eyeball and keeps the eyeball in its shape. The sclera is a connecting and supporting tissue in the human eyes. It is termed as a protective, tough white layer.
2. Cornea: The front transparent part of the sclera is called the “cornea”. First of all, light enters the eye through the cornea. 
3. Iris: This is the dark, muscular tissue having a ring-like structure. Iris is located behind the cornea. The colour of the eye defines the colour of the human eye. The main function of the iris is to regulate exposure to light rays.
4. Pupil: Small opening in the iris of the human eye is called a “pupil”. The iris controls the size of the pupil. It also controls the amount of light entering the eyes.
5. Lens: The transparent structure lens is located at the back of the pupil. Ciliary muscles help the lens to focus the light on the retina. Ciliary muscles help the lens to change its shape. So, the lens can become thinner to focus on distant objects and thicker to focus on nearby objects.
6. Retina: Retina helps to convert electrical impulses from the image of the lens. These electrical impulses are transmitted to the brain via the optic nerve. It consists of multiple nerve cells. This is also a light-sensitive layer. 
7. Optic nerves: Two types of optic nerves are there. Example- cones and rods. The cones are more sensitive to bright light. It helps to detect detailed colour and central vision. The rods are more sensitive to dim lights. So, for peripheral vision, rod optic nerves are helpful. 
8. Different muscles: There are six muscles in the eyes. They are medial rectus, lateral rectus, superior rectus,inferior rectus, inferior oblique and superior oblique. These control the movement of the eyes from multiple tensions and torques. 

The function of the human eye

The human eye functions as a camera. It works as an electronic device that focuses the light and lets the light in to produce images. In simple words, light rays deflected from or by any distant object falls on the retina. These light rays pass through different mediums in the eyes- cornea, crystalline lens, aqueous humour, lens and vitreous humour, etc.

After refracting from different mediums in the eye, the light rays are finally received and focused on the retina. The retina constitutes the rods and cones (optic nerve) that detect the intensity and frequency of light. The inverted image formed on the retina is passed to the brain using optic nerves that correct it and form a straight image.

Conclusion

The anatomy of the human eye is an important part of the CBSE class 11th syllabus. The function of the sclera in the human eye is important to know about detailed functioning.