Can make head hurt.

Vergence/accommodation conflict is often quoted as one of the contributors to why some people experience discomfort when watching stereoscopic 3D (S3D) films or TV.

When we look at a nearby object in real life, we focus our eyes at it (accommodation) and we rotate our eyeballs inward to allow each eye’s gaze to cross at the object (vergence). Distinct groups of muscles are in charge of these two operations and typically work in unison.

However, when we watch an S3D film, we focus at the screen plane, but we may converge our eyes in front of or behind the screen. This decoupling of vergence and accomodation can contribute to eye muscle fatigue.