Video Transcript

Henry Greene: I’d like to talk a little bit today about visual acuity, loss of central vision and how it impacts our day to day lives. I had a patient that came to me once who was using a four power telescope to help her see further away. She explained to me that without the telescope she could only see to the length of her arm, beyond that everything was so blurry she couldn’t see it. And what she liked about the telescope is that in effect it made her arm 4 times larger. What she said was now I can see my friends and family at distances I couldn’t see them before. Before that I had to get up so close to them that it was kind of inconvenient or if it was someone I really didn’t know it was even sort of inappropriate. So the value of a telescopic device for folks that are visually impaired is to extend their ability to see further away then they normally can. We define a visual radius as the furthest distance an individual can see. There’s a range of distances that are the normal ones that we engage in social activities and we call that the social range, and that’s roughly from 5 feet to 20 feet. So the goal of a device that can help you see further in the distance is to extend your visual radius, the furthest distance you can see somebody’s face for instance, far enough into the social range to be able to be of value. For instance, if I can only see someone’s face from 4ft away and I use a 4 power telescope, it now makes the image 4 times larger, but the value is that now I can see them 4 times further away or 16ft. Far enough into the social range to be of value. However, if I can only see their face at 1ft and I could enlarge it 4 times, I’d only move it out to 4 ft, not far enough into the social range to be of functional value. So another way to think about vision is whether or not I can see far enough into the social range to be of value. If not then we have to explore telescopic devices to help extend your ability to see into that range.