If the film is based on a true story, the actor will try and get to know the life of who they are emulating. This could include researching and/or living with the person, so as to pick up their mannerisms and idiosyncrasies.
Take Daniel Day-Lewis, for instance, known for his intense style of acting. He starts prepping for his roles months in advance, and takes on the character's persona the entire time. This is even before filming begins.
This would be termed 'method' acting, described as a naturalistic style of acting where the actor closely identifies with the character to be portrayed.
During the shooting of 'Gangs of New York', he refused to wear a thick coat saying that they didn't exist in the 19th century. He ended up getting sick and doctors forced him to take antibiotics.
For the movie 'My Left Foot', Day-Lewis spent quite a bit of time in a wheelchair, and got spoon-fed, so he could truly feel what it is like to have a physical disability. For that role, he won an Oscar for his portrayal of Christy Brown, an artist and writer born with cerebral palsy.
You've heard of actors gaining pounds of fat, or bulk of muscle to make themselves believable on the big screen. Or even something as simple as changing their hair style. But how does it work if you were to play a blind person?
If you have your eyes open and 'pretend' you can't see, well, you know how well that would work. Sure, you could close your eyes, but blind people don't do that. Actor Neil Patrick Harris had to worry about just this, for his new role in the movie 'Beastly'.
According to Harris, even picking up a glass of water while pretending not to see was difficult, so he sought a solution.
Blind lenses are special effect lenses that provide no vision. You are unable to see anything when you wear 'blind' contacts. Thus, it is perfect for people who need to really know what it would feel like to be blind.
Blind contact lenses are great for actors who take their work seriously, and want to come across genuine when portraying someone with a visual impairment.
However, this may not work out so well for you, if you're not an actor and wanting to be yourself. Thus, a similar contact lens, but one you can see through is called Walking Dead. Go fool them into thinking you can't see, when you very well can.