The technique used to see the object while keeping the distance between the object and the eye unchanged is called accommodation. The vision in which near objects cannot be seen clearly is called hypermetropia. This disease is cured by using convex lens. Vision that does not see distant objects clearly is called myopia. This disease is cured by using concave lenses.

Light rays from illuminated objects fall on the cornea of the eye. Light rays from the cornea enter the lens through the pupil. Reflected from the lens to the retina. An inverted image of an object is formed on the retina. The resulting reflection stimulates the photosensitive (rod and cone) cells of the retina. This stimulus reaches the brain’s visual center (optic lobe) via the optic nerve. As a result, people see an upright reflection of the object.

The cone-shaped pigment cells in the retina of the eye are called cone cells. It contains purple pigments called iodopsin and cyanopsin. It contains a protein called photopsin. Its number is about 60-70 lakhs. Each angle cell is 40 micrometers long and 3-5 micrometers thick. It contains three types of cells. Red, green and blue cells. It is suitable for viewing in bright light. White color is seen when three types of angles are equally excited. Color blindness occurs when the cornea is destroyed.

The long and rod-shaped pigment cells in the retina of the eye are called rod cells. It contains vitamin-A and a reddish purple pigment protein called rhodopsin. Its number is about 12 crore 50 lakhs. Each rod cell is 50 micrometers long and 2 micrometers thick. It is useful for dim light viewing. If the red blood cells are destroyed, night blindness occurs.

Human eyes have three types of glands.
(i) Lacrimal glands: It is located above and in front of the eyeball. Ashra (अभुद्थ) is secreted from this gland. Tears keep the eyes moist and sterile.
(ii) Harderian glands: It is located behind the eyeball at the base of the eye. The oily substance secreted by these glands lubricates the cornea and prevents evaporation of tears.
(iii) Meibomian glands: It is located in the corner of eyeball. The oily substance secreted by these glands lubricates the cornea and prevents evaporation of tears.

2 oblique muscles.
(i) Superior oblique muscle: It helps the eyeball to rotate along the axis between the optic nerve and the cornea.
(ii) Inferior Oblique Muscle: It acts opposite to the superior oblique muscle.

4 rectus muscles.
(i) Lateral Rectus Muscle : It helps rotate the eyeball outwards.
(ii) Medial rectus muscle : It helps in inward rotation of the eyeball.
(iii) Superior rectus muscle : It helps the eyeball to rotate upwards.
(iv) Inferior rectus muscle: It helps the eyeball to rotate downwards.

The orb is attached to the orbit by 6 muscles. Muscles are double. Rectus muscle and oblique muscle.
1. Rectus muscle: 4 rectus muscles.
(i) Lateral Rectus Muscle : It helps rotate the eyeball outwards.
(ii) Medial rectus muscle : It helps in inward rotation of the eyeball.
(iii) Superior rectus muscle : It helps the eyeball to rotate upwards.
(iv) Inferior rectus muscle: It helps the eyeball to rotate downwards.
2. Oblique muscles: 2 oblique muscles.
(i) Superior oblique muscle: It helps the eyeball to rotate along the axis between the optic nerve and the cornea.
(ii) Inferior Oblique Muscle: It acts opposite to the superior oblique muscle.

The hair above the eyelid is called eye brow. It prevents sweat from the forehead from entering the eyes.

The eyelash is called Akshipaksha. It prevents dust and germs from entering the eyes.