Star Trek: 10 Things You Didn't Know About Geordi's VISOR
2. The Mind-Control Powers Of The VISOR
Geordi La Forge was captured by Romulans while on vacation in the episode The Mind's Eye. Using the VISOR's interface with Geordi's brain, they were able to force him to see horrible images and eventually conditioned his mind to follow their orders.
Using this mind-control method, the Romulans hoped to get Geordi to assassinate a Klingon named Vagh in order to spark conflict between the Klingon Empire and the Federation, which they nearly succeeded at.
Luckily, Data began detecting strange E-band emissions aboard the ship, and was able to figure out that they were being used to interface with the VISOR. It was later discovered that Kell, one of the Klingons visiting the Enterprise, was actually a Romulan conspirator who was feeding Geordi commands though E-bands.
It's truly terrifying to know that the same technology that allowed Geordi to see could also be used to command his brain.