Peripheral Vision

 Healthy eyes do more than just allow you to focus farther as well nearer. 

Eyes also help you to sense things which are not in your direct sight. This is also known as side vision or peripheral vision. This is important during cycling, reading or playing sports. When you look at something, you use central vision to focus on details while peripheral vision to know more about the surroundings.

Let us perform this activity to understand peripheral vision better.

We will need some color markers and a paper strip. Let us make a small paper roll from the strip. Small Paper rolls are used to write combinations of color, shape and text.  We need to mark angles as well. These can be written on a piece of paper. 

Tejas will help me in setting things up as well as doing this activity. 

Let us place a 90 degree mark right in front of his right eye.  With the help of his fist, Tejas approximates the 80 degree mark, a step of 10 degrees. With his fingers extended all the way, he marks 60 degrees, an increment of 20 degrees. 

With all angles marked, Tejas looks straight at his thumb of left hand placed on the table. He stretches his right hand all the way behind him. 

Let me place a small paper roll marked with Shape, Color and Text on his right hand thumb. He is not aware of what is written on it. 

He will slowly move his right hand towards the left hand placed on the table. While doing this, he will try to identify 4 things with his right eye. Motion, Color, Shape and Text. This will happen at various angles during the movement of his hand. 

He detects motion first, followed by color, shape and finally text. This activity can be repeated many times and an approximate angle for each can be calculated.

Same can be done with another eye as well. 

Now let us understand why he is able to read text only when it is almost in front of his eye. 

This is the internal structure of the eye. 

Let us consider his right eye for now. 

The cornea is the clear outer layer at the front of the eye. It allows light to enter the eye. It provides approximately 65 to 75 percent of the focussing power of the eye.

The remainder of the focusing power of the eye is provided by the crystalline lens, located directly behind the pupil.

The retina is the sensory membrane that lines the inner surface of the back of the eyeball. It has special cells known as photoreceptors.

There are two types of photoreceptors - rods and cones. 

Rod photoreceptors detect motion, provide black-and-white vision and function well in low light. Cones are responsible for central vision and color vision

Rods are located throughout the retina; cones are concentrated in a small central area of the retina called the macula. At the center of the macula is a small depression called the fovea. The fovea contains only cone photoreceptors and is the point in the retina responsible for maximum visual acuity and color vision.

Our eye is like a pinhole camera. 

Rays reach this region where only cone cells are present. All other rays reach regions where there are mostly rod cells. 

This is why Tejas could read a word only when it is in front of his eye. 

Do try this at home and check your peripheral or side vision.

Thank You.