vision impairment refers to when you lose part or all of your ability to see (or vision). The impairment must persist even with the use of eyeglasses, contact lenses, medication, or surgery.
The types of vision impairments are low visual acuity, blindness, and legal blindness (which varies for each country):
Low visual acuity, also known as moderate visual impairment, is a visual acuity between 20/70 and 20/400 with your best corrected vision, or a visual field of no more than 20 degrees
Legal blindness in the United States is a visual acuity of 20/200 or worse with your best corrected vision or a visual field of no more than 20 degrees.