Why would you need night vision glasses?

The pupil dilates in low light conditions to allow more light onto the retina. This will, in many people, result in more near-sighted vision at night than during the day.

If you normally do not wear glasses or have progressed to the point of needing bifocal, trifocal, or progressive lenses (presbyopia) you may need a different prescription to fully correct your vision in low-light environments.