[Physics Class Notes] on Blind, Visually Impaired, Optical Low Vision Aids Pdf for Exam

The Human Eye

The human eye is an essential sense organ that allows us to see the beautiful world. The specialty of this optical instrument lies hereunder:

The eye is the best camera created by God. Yet, some people face difficulty in viewing the nearby or far off objects clearly, while some people don’t get the opportunity to see the world with their open eyes. 

Keeping in mind the needs of every individual, around 1285, one of the eyeglass inventors named Salvino D’Armate invented the first vision aid called the reading stone. Slowly and gradually, by modifying technology, visually impaired people also got the chance to look and feel the world around them. 

In this article, you will learn about the types of optical instruments that have tossed the scenario of the world by changing the way people see the world around them. So, let us study the optical vision aids.

Optical Low Vision Aids

Myopia: Nearsightedness

Many people face difficulty viewing nearby objects; however, they can see the far off objects with ease. This type of optical defect is known as Myopia. 

In the above figure, we can see that the shape of the eye bends the light, and the image focuses in front of the retina rather than focusing on it.

This optical defect can be rectified by using a Concave Lens. The figure below demonstrates the correction of Myopia:

Hypermetropia: Longsightedness

An optical defect in which a person can see the far off objects but find difficulties in viewing the nearby objects, such a defect is called the Hypermetropia. This is how it happens:

  

Hypermetropia is a common problem where a large image is formed because of the large focal length, causing the nearby objects to appear to blur. 

This defect can be corrected by using a converging lens or a convex lens. The figure below demonstrates the way to correct this problem:

From the above diagram, we can see that a convex lens is kept in front of the eye lens, which forms a virtual image of the near point of the eye, i.e., at a distance of 25 cm, the image gets focused on the retina.

Astigmatism

Astigmatism is a type of refractive error, or we can say it is an imperfection that comes in the curvature of the cornea or lens of the eye such that eyes cannot focus the light uniformly on the retina. 

The parallel rays of light coming from infinity form multiple focal points with the accommodation at rest because of which the objects seem blurry at all distances. The figure below demonstrates the astigmatism defect:

     

Astigmatic cornea distorts the focus of light in front or beyond the retina. The figure below shows why objects seem blurry at all times:

For correcting this defect,  a particular lens is used called the cylindrical lenses (contact lenses). The figure below demonstrates the correction:

Presbyopia

An aging eye defect because of which person loses the ability to view the objects clearly with the passing time. It is a physiological inability to accommodate the near vision. A person has to hold a reading material far away to avoid headaches and eye strain. The below figure demonstrates this defect: 

       

Since this defect is a progressive worsening issue with the age so, people dealing with this issue can use bifocal or progressive eye lenses as a temporary aid for viewing the nearby and far objects, where bifocal lenses have the two following sections:

Primary Section: It is a large section that helps to correct the distance vision.

Secondary Section: It helps us to see nearby objects.

Visual Aids for Visually Impaired

Who are blind people? Can they see the world around them? The answer to this question is sad No! But they have a superior power to feel; this ability is used as an aid to help them read things as normal people do. This aid is the Braille System.

In the year 1824, the Braille system was invented by Louis Braille. One of the essential aids for Visually Impaired people is the Braille system. Braille or breɪl is the strategic writing system for blind people. 

In this system, there are six dots, raised in different patterns to form 26 letters of English; this arrangement of dots, to give English alphabets, is the Braille alphabet. The image below shows the Braille script from A to Z:

The braille system comprises equivalents for punctuation marks and also imparts symbols to show letter groupings. Braille alphabets are read by moving the hand or hands from left to right along each line.