Category: Biology Second Paper

Advantages of binocular vision

1. A reflection of an object is seen with both eyes.
2. Objects can be deeply understood.
3. The field of vision is much larger.
4. Different tasks can be done correctly.
5. Binocular vision can accurately assess the shape and depth of an object.
6. If there is a problem in one eye, it can be seen by the other eye.
7. Distance of objects can be sensed accurately.
8. Three-dimensional vision of objects can be observed.

Binocular or Stereoscopic Vision

When a three-dimensional image of an object is formed in two eyes of a person, it is called binocular vision.
A characteristic or condition of binocular vision
1. The object must be present in the retina of both eyes.
2. A similar image of the object will be formed on the retina of both eyes.
3. The two observatories will meet at one place.

Adaptation techniques of eye

1. Near object vision technique: During near object vision the circular muscle of the ciliary body contracts and the suspensory ligament is stretched. It increases the curvature of the lens. The lens becomes thicker and shorter and the focal length decreases. Light rays from the object fall on the retina and an image is formed.
2. Techniques for viewing distant objects: During viewing of distant objects, the circular muscle of the ciliary body stretches and the suspensory ligament contracts. It reduces the curvature of the lens. The lens becomes narrower and longer and the focal length increases. Light rays from the object fall on the retina and an image is formed.

Accommodation

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.

Formation of Image and Vision

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.

Cone cell of eye

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.

Rod cell of eye

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.

Eye glands

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.