The Human eye is the organ which gives us the sense of sight, allowing us to observe and learn more about the surrounding world than we do with any of the other four senses. Most people probably would agree that sight is the sense they value more than all the rest.
Anatomy of Human Eye:
Before entering with specific parts of human eye, we should have gross idea regarding its anatomy-
The sclera is the tough white sheath that forms the outer-layer of the ball. It is also referred to by other terms, including the sclerotic and the sclerotic coat( both having exactly the same meaning as the sclera)
- Provide protection for its delicate internal parts
- Meet the purpose of attachment of the extra ocular muscles that enable eyes to move.
- Maintains the shape of the eye
The conjunctiva is a clear mucous membrane consisting of cell and underlying basement membrane that covers the sclera( white part of the eye) and lines the inside of the eyelids.
- It helps lubricate the eye by producing mucus and tears, although a smaller volume of tears than the lacrimal gland.
- It also contributes to immune surveillance and helps to prevent the entrance of microbes into the eye
The pupil is the hole in the center of the iris that light passes through the iris muscles control its size.
- Regulates the amount of light passing through to the retina
- Acts as a aperture of a camera
- When dilated by mydriatic agent, causes the beautification of eyes followed by the ancient ladies
The cornea is the transparent circular part in the front of the human eyeball. It has an important optical function as it refracts light entering the eye through the pupil and onto the lens.
- It refracts the light entering the eye through the pupil and onto the lens.
- Protects the pupil and iris from external environment.
The iris is the colored part of the eye. It is a thin diaphragm composed mostly of connective tissue and smooth muscle fibers. The iris lies between the cornea and crystalline lens.
- Gives our eyes a particular color example blue, green and brown
- Responsible for controlling the diameter and size of the pupils
- Responsible for controlling the amount of light reaching the pupil.
The lens is transparent structure enclosed in a thin transparent capsule. It is located behind the pupil of the eye and encircled by the ciliary processes.
- Producing image of the object on to the retina
- Acts like the lens of a camera
- The lens of the eye helps to refract light travelling through the eye ( which first refracted by the cornea) the lens focuses light into an image on the retina. It is able to do this because the shape of the lens is changed according to the distance from the eye of the objects the person is looking at
This adjustment of shape of the lens is called accommodation and is achieved by the contraction and relaxation of the cilliary muscle.
Contraction and relaxation of the ciliary muscle alters curvature of the lens.
- Helps to alt the curvature of the lens
- Changes focal length of the lens
The choroid is the layer of the eyeball located between the retina and sclera. It is a thin highly vascular( i.e. it contains blood vessels) membrane.
- It supplies blood to the retina
- Contains a pigment that absorbs excess light and so prevents blurred vision (due to too much light on the retina).
- Provides oxygen and nourishment to the outer layers of the retina.