This bug is related to MC-51953, which was never actually resolved. Original bug was "resolved" by increasing default FOV, but the screen distortion still persists, causing motion sickness and headaches for many players.

Environment becomes more distorted near the edges of the screen. Blocks appear stretched and warped the further from the center they are. This is easily observed by watching the corners of the screen as you slowly move the camera around. The blocks appear to "curve" slightly.