Eyes are made of chemicals that react to our atmosphere. I consider people who never need spectacles as very fortunate. All chemicals fade in time and as such our sight alters.
Last week I did get worried about my sight. I thought I was going blind, or at least having perception issues.
Shops I regularly use had floor plans that appeared to change - even though I know they were the same - one seemed to have a split-level shop floor. Other shops seemed to have shelves that blurred when I turned my head.
I was concerned that if I wasn't going blind, there might be a neurological problem behind my sight issues.
After a bit of thinking, I came to a conclusion. The answer is easy - I was looking through the wrong section of my bi-focal glasses.