In-Universe answer ------------------ The entry in the [official Star Trek Encyclopaedia][1] states that Borg implants are added to each drone **depending on the needs of the collective**. Different eyepieces are seen because the drones will need different sensing capabilities to do their assigned jobs. It makes little sense to outfit a Medical Drone with the ability to target objects at great distance, for example. ![enter image description here][2] Tactical Drones, for example seem to have long-lens type eyepieces on their right whereas Medical Drones appear to have a microscoping eyepiece with multiple lenses. Normal 'labor/maintenance-type' drones seem to have the bog-standard holographic eyepieces that we see in TNG: I, Borg whereas the [Borg Queen's eyepiece][3] seems to be wholly internal. ![enter image description here][4] Regarding the ***side*** of the head that the device is fitted to, there are a couple of possible reasons: - To match the side that the prosthetic arm will be fitted. - As twinned pairs (Tactical borg will often walk with a "left-eye" and a "right-eye" [together][5] for example) - As @Einer says, if someone has a pre-existing deficiency in one eye, it's reasonable to presume the Borg will replace that eye as a priority - **Handedness** seems to be hard-wired into human (and alien) brains. It makes sense not to fight against an *existing* predisposition when there's a completely free choice. Out of universe answer --------------- Gil Mosko, makeup artist for TNG, Voyager and First Contact describes the [evolution of the eyepieces][6] over time. The side chosen appears to be totally random, as part of an effort to create a "unique feel" for the alien nature of the Borg. > **Brandon:** *What was it like working on the Borg makeup "upgrades" for > Star Trek: First Contact and then carrying those over for Star Trek: > Voyager? Specifically, can you give us any insight into the process of > enhancing the look of the TV Borg for their big screen debut?* > > **Gil:** *The Borg had been relatively standardized by the time they were > used in one of the films. Like any television to big screen makeup, we > had to be more careful about details. The painting of the background > became an airbrush process beginning with an off-white background. It > then had beige and taupe air brushed in a mottled pattern. Every hose > that connected to skin had a foam transition. These looked almost like > bullet hits, and then the tubing was glued to the inside circle. **Our > use of “mechanical” looking parts became more flamboyant. We were even > provided with the centers of electronic wristwatches that would have > moving elements inside them.*** Michael Westmore, Makeup Supervisor for TNG, Voyager and First Contact seems to be [suggesting][7] that the eyepieces were styled to fit the headpieces, rather than the other way around; > **How has the Borg make-up evolved?** > > I had to figure out what to do with the hands and the head. > **They had these helmet-like devices on that had openings in them, and > they could be scarred. It was a very quick make-up that way, the > helmets were all pre-painted, even if there was a hole and an opening,** > that area could have been pre-painted with the same colour make-up > that we'd use on their face. > > It was just a matter of putting a foundation on their face, air > brushing some shadows into it, slipping the helmets onto them and **just > gluing down around the edges and putting on the eye piece, of which > the original eye pieces didn't have any mechanical workings or lights > to them at all.** [1]: http://en.memory-alpha.org/wiki/Star_Trek_Encyclopedia [2]: https://i.sstatic.net/8QO6z.png [3]: http://i127.photobucket.com/albums/p154/kevoris/bqs3.jpg [4]: https://i.sstatic.net/wgSND.jpg [5]: http://cdn.smosh.com/sites/default/files/ftpuploads/bloguploads/0813/the-borg-star-trek.jpg [6]: http://trekinitiative.wikia.com/wiki/User_blog:Brandon_Rhea/Interview_with_Gil_Mosko [7]: http://www.bbc.co.uk/cult/st/interviews/westmore/page8.shtml