Since the Player only displays either the Left Eye or Right Eye, it is difficult and tedious to edit and grade one eye and create the same changes for the other eye. An easy way for you to make sure any editing or grading is automatically applied from one eye to the other is by using the Sync option. When this feature is enabled, any editing or grading you do on one eye is applied to the other.
The Sync option only works if you do not break the sync. For example, if you enable Sync and draw a geometry, whatever you do to that geometry on one eye will be duplicated on the other. The moment you disable the Sync option and change the geometry on one eye (e.g., colour, position, vertex, etc.), that geometry will never be synced again when you re-enable Sync.