Your idea of what blindness is is well, biased towards hollywood's take on blindness, basically full black blindness is EXTREMELY rare, what classifies as blindness in the medical sense is a vision impairment that cannot be treated with modern medicine that is detrimental to normal life and there are tiers to it.
A example of the more commonly known full blindness would be someone who can see shapes but not details, most people who are considered fully blind can actually make out shapes at very close range but cannot make out any details, it's like a world of white, hence why they need extremely dark shades.
What i am is legally blind due to a illness when i was younger, this is a vision impairment where i can see and even make out faces up close and even see things if they are big enough at mid range with proper glasses, but have permanent damage in my field of vision, in my case i cannot see well out of my left eye as it has a severe "twist" in the center of my vision and blurring, enough that i cannot legally do anything that involves motor vehicles and need to wear glasses pretty much at all times.
My right eye is not great either but i can see with it effectively with proper lenses.
