How to explain others about Stargardt's?

(From wikipedia)

As only 1 in 20,000 people are impacted, most of the people are unaware of the condition. Also, it is difficult for the sighted to understand our condition. When my vision was better even I couldn't understand what was happening to me or what would be in store for me in the future.

   
First step is try to tell others that it is not some bad case of uncorrectable myopia.

Peripheral Vision 

You can explain to others that you are losing your central vision. For all human beings there is a central vision and peipheral vision. Central vision helps us to perceive details, to read, to recognize faces whereas peripheral vision (view not in direct line of focus) helps us have a broader view. You can hold your visiting card or identity card in front of them and show them if they are looking directly and using their central vision and are able to read. Then, ask them to look sideways (i.e. use peripheral vision) and see if they can read. They will tell you that they can make out the broader picture (that you are holding a card in front of them), they can notice the colour, shape but they cannot read. Explain to them that if they use their side vision, i.e. look straight ans try to perceive the view on their side they will be able to notice big objects, like trees, people walking, but will miss details about them.

Brain fudge 

Reading or recognition process is part visual and part processed by brain (association). As we can only see partially, our brain ends up guessing for us. Imagine a jigsaw puzzle with missing pieces, that's how we see the world. But for most of us, we do not see blank spaces for the missing blocks of view. Our brain recreates the blank space by filling in things from memory. So I will not see a manhole in the road sometimes, because my eyes couldn't spot it and my brain processed the image as smooth road. I misread words. In later stages of SD, some people also experience visual hallucinations - Charles Bonnet's Syndrome