system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why can you buy very cheap reading glasses in shops but there is no cheap equivalent for those with short-sight?

I have noticed you can buy reading glasses for £1 in certain places, but nowhere are short-sighted glasses sold for this price or indeed anywhere except opticians. Why is this? Is there a dramatic difference in how they are manufactured?
gpt
Reading glasses have a really specific purpose, so they don't have to be custom made.  You can put your reading material at a whatever distance they will be in focus, to make up for the lack of accuracy in the lens.

Short-sighted people have very specific focus problems, possibly different in each eye. They also need to be able to see objects are extremely variable distances.  It's impossible to make generic glasses for this purpose; unless both lenses are just right it will be blurry and possibly give headaches.