Human Eye

There are following main parts in the human eye.

1. Cornea: The cornea is a part of the sclerotic coat. It is white, hard and transparent because it does not contain any blood vessels.

2. Aqueous humor: The space between the cornea and the pupil is called the anterior chamber, and is filled with a transparent substance called aqueous humor.

3. Pupil: It is the round black spot in front of eye. It manages the amount of light entering the eyes. In case of dim light pupil dilate to allow more light to enter the eyes. In case of strong light pupil constrict allowing less light to enter.

4. Irish: They control the size of opening of pupil.

5. Lens: Lens lies behind the pupil. This enables us to see distant objects clearly. The minimum distance of clear vision is 25 cm.

6. Retina: Retina works like a screen. Retina is full of light and colour sensitive cells. The cells in the eye are of two types - rod cells and cone cells. The rod cells are sensitive to dim light. The cone cells are sensitive to bright light and colour.

7. Vitreous humor: The space between the lens and the retina is called the oosterior chamber and is filled with a transparent substance called vitreous humor.

• One eye is having a field of vision of about 150 degrees.

• Both the eyes enable us to see up to a field of 180 degrees.

• Myopia

  - Also known as near-sightedness.

  - A person with myopia can see nearby objects clearly but cannot see distant objects clearly.

  - In a myopic eye, the image of a distant object is formed in front of the retina

  - This defect can be corrected by using a concave lens of suitable power.

• Hypermetropia

  - Hypermetropia is also known as far-sightedness.

  - A person with hypermetropia can see distant objects clearly but cannot see nearby objects clearly.

  - This is because the light rays from a nearby object are focused at a point behind the retina.

  - This defect can be corrected by using a convex lens of appropriate power.

• Presbyopia

  - It arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens.

  - Such people often require bifocal lenses.