I think the answer might be
As Shahriar pointed out
The acrostic spells DISGUISE
Do you think that I can hide you from your friends?
Sunglasses can be used as part of a disguise.
I'll have them seeing you through a different lens.
Glasses have lenses
So don't be surprised if you can't recognize,
It's not always easy to recognise a person if they are wearing sunglasses.
Given that I'm a very familiar guise.
Sunglasses are worn by people in many different situations, especially on a sunny day.
Underneath all these lies, I'll protect what you hide,
Your eyes, the windows to the soul.
I'll convince all their eyes, your secret is what I pride.
Your eyes can often give away what you are thinking.
So beware what you see, this face smiling happily.
Ere what you were, will be forced upon you unhappily.
Even though somebody appears to be smiling, you cannot always tell their state of mind unless you see there eyes.