'1000-lb Sisters' Star Amy Undergoes Surgery to Correct Lazy Eye, on Video

"1000-lb Sisters" star Amy Slaton had a surgery that had nothing to do with her weight ... instead, it was all about her vision.

TMZ obtained an exclusive clip from an upcoming "1000-lb Sisters" episode showing the moment Amy goes under the knife to correct her lazy eye.

In 2015 Amy posted a YouTube video explaining that she had ocular toxoplasmosis ... an infection in the eye caused by a parasite. It is a very rare eye condition she's had since birth that caused her to become legally blind.

Doctors actually had to operate on both of Amy's eyes ... and her husband, Brian Lovvorn, was super nervous when he talked to a film crew while waiting for the surgery to finish up ... revealing he was most concerned about Amy possibly not waking up from the anesthesia.

Fortunately, the surgery was a success ... and Amy's got a new look ... and some more confidence.

The full episode airs March 3 at 9 PM ET/PT on TLC.