Introduction to Assistive Technology for Vision Impairments

1.3.1: How is vision loss measured?

Do you Know?

A visual field is the total spatial area, which is visible to you, while your eyes are in a stationary position, and you are looking straight at an object. This field is divided into central and peripheral zones.  

Vision impairment may be caused by a loss of visual acuity, where the eye does not see objects as clearly or sharply as usual. A person with a visual acuity of 20/70 can see at 20 feet what someone with normal sight can see at 70 feet.
Vision impairment may also be caused by a loss of visual field, where the eye cannot see as wide an area as usual without moving the eyes or turning the head. A normal visual field is about 160-170 degrees horizontally.
As per the definition published by the World Health Organization, ‘low vision’ is visual acuity between 20/70 and 20/400, with the best possible correction, or a visual field of 20 degrees or less. ‘Blindness’ is defined as a visual acuity worse than 20/400, with the best possible correction, or a visual field of 10 degrees or less.
From the videos, we now know how our eyes are perceiving light, images, color, and motion in our surroundings, support in making 2D and 3D interpretations for the brain, and how an impairment in the vision affects this process.
Here’s a quick simulation activity to help you understand the experiences of different types of vision impairment.

Additional Notes and References

Check out this website to read more about eye tests, how scores are calculated and how the result is.

What is Visual Acuity? (Tests, Charts & Scores Explained) (visioncenter.org)

Activity - 5mins
Activity – 5mins Take a sheet of printed text (Newspaper/Advertisement/letter/). Place it on a table or against a wall for hands-free reading. Now read the text under the following conditions:
  • Read at a convenient distance suitable for you.
  • Move away from the sheet and try reading it.
  • Read with one of your eyes closed.
  • Factors that restrict interest of industries and businesses from entering Assistive Technology sector are Customization and fragmented market- which leads to supply chain and inventory challenges.
  • Try wearing a pair of glasses with spots and dust on it
  • Roll a sheet of paper and read the text through the rolled paper.
Reflect on your experience under each condition. This this help you understand how no two people with vision impairment have the similar conditions? Here, each of the clauses gives you a glance of impairments like shortsightedness, farsightedness, tunnel vision, central vision loss, etc. Now let’s move on to the next section to understand each of these in detail and how vision impairment is also not limited to these.