Legal blindness is defined on the basis of Both eyes – if the degree of impairment is in one eye only the individual is not considered legally blind.
If the good eye is good enough, a person legally blind in one eye can drive a car in most states of USA.
Legal blindness refers to clinically measured visual acuity of 20/200 in the better eye with best correction, or visual field of 20 degrees or less. An individual with one eye correctable to better than 20/200 and a visual field of better than 20 degrees is not considered legally blind.
In Pakistan as far as I know you can get a driving licence by obtaining a doctors certificate from their approved doc.
In UK. DVLA (Driver and Vehicle Licensing Agency) says:
"If you have sight in only one eye you may still be able to meet the visual standards for driving provided you meet some conditions.
It may take up to three months for you to adapt safely to driving with one eye, so please be prepared for this."