Screen, glass with shutters or fogged/ribbed glass.
Screens would work by distorting the vision view between the outside and inside but aren't the best for privacy.
Glass doors with shutters can help, but requires the user to constantly change the angle of the shutters. This is a good and bad thing, giving the user the freedom to let a specific amount of light in, or shutting them completely for full privacy.
Fogged/Ribbed Glass is ideal since it is still glass, but has patterns or fog to distort the light entering, allowing for privacy. It is the best of both worlds, and can be installed anywhere.
If you want to get REALLY fancy, Smart Glass is another expensive option, but allows the user to dim glass to their liking for optimal light and privacy.