Anyone nearsighted can estimate the strength of their nearsightedness by looking at an object close enough to be perfectly clear, then increasing the distance until the farthest where it appears clear. Take that distance in meters and invert it. The result is the amount of nearsightedness in diopters. For example : you see clear up to 50 cm away, or 0.5m, you have 2 diopters. You see clear up to 10 cm away, 0.1m you have 10 diopters.
Anyone with normal (or corrected) vision can estimate the strength of a magnifying lens by the same method. Most magnifying glasses are 5 to 20 diopters.
Well, perhaps not strictly anyone can, but you get the idea.
Look for 'starburst' here https://visionsimulations.com/ Sadly the simulation site is down because of the new Cross-Origin restrictions on images in canvases but perhaps you can see what it looks like in the preview images on the main page and if you google 'starburst vision'.