Today the US Patent & Trademark Office published a patent application from Apple that relates to Head Mounted Devices (HMDs) with optical module positioning systems. Specific mechanisms are designed to accommodate users with different interpupillary distances. Interpupillary distance (PD) is a measurement of the distance between the centers of your two eyes. This measurement is used to properly align the centre of lenses with the centre of your eyes. If the centers of the lenses are not aligned properly, then you may experience eyestrain, headaches, distorted vision...