All this talk about when a prescription becomes bad and bragging about how bad you are and still not wearing glasses...
There are no hard and fast rules. How clearly do you want to see? At -2.00, I could make my way around without anything, but I'd rather it looks sharp. Someone else at -2.00 might not. How big are your pupils? Looking through bigger apertures softens the focus, so if you've got huge pupils you'll probably see worse than someone with the same prescription but small pupils. Is there astigmatism? Unlike short and long sight (unless it's really bad), astigmatism will mess vision up at any distance, so if you've got a reasonable amount (I have another -1.25 in astigmatism, making me -3.25 in some directions) you'll need glasses more.
So i have really bad eyesight ... -4.75
i recommend contacts !!