Air carrier Captain reported the First Officer was wearing a pair of smart glasses and suggested that the company and/or FAA should offer concrete policy guidance on whether it was appropriate and safe to wear those glasses in the flight deck.

Narrative

On taxi out; my FO put on what I thought might be prescription glasses but which I eventually came to realize were Ray Ban Meta glasses. After noticing the cameras on the corners of the glasses; I found myself wondering if he was recording me or our flight. Shortly after takeoff; he put the glasses away and didn't put them back on. I didn't say anything to the FO. That night; I researched the glasses and learned more about their features. I also searched the FOM to see if references in the personal electronic devices section mentioned these at all. I didn't see concrete guidance. I decided that if he put the glasses on during a subsequent flight that I would bring it up.The next day on our way to ZZZ; the opportunity presented itself at cruise. I asked what the glasses were and he confirmed they were Meta glasses. I asked if they were prescription and he said no but that they can be and that he uses them because they have transitional lenses which are nice for changing light levels. I asked if they were permitted at Company and he said he had looked that up and hadn't seen any prohibitions beyond the use of recording with Personal Electronic Devices (PEDs) and such. He proceeded to go on to say he turns off the camera and sound and video portions of the glasses with a switch. He asked if I would be more comfortable with him not wearing them and I said yes. He said that was no problem at all. He did not bring the glasses out again.While I will give him the benefit of the doubt for all this that he was in compliance with the current FOM as written; I believe it would be highly beneficial for the company or the FAA to offer more direct guidance on the acceptability of use of smart glasses on the flight deck. I come down on the side of these glasses increasing distractions on the flight deck; even if unintended. I can imagine pilots questioning what they say due to thinking they might be recorded or pilots wearing the glasses being distracted by not following approved guidance (such as using the glasses for unapproved activities like listening; texting; recording; etc). To my knowledge there is no way for the non-wearer to know if the glasses are being used appropriately or not. I can envision conflict on the flight deck between pilots with differing views on the appropriateness or acceptability of these devices in flight. All of this supports the need for the company and/or FAA to offer concrete policy guidance on smart glasses as this will certainly become a more widely used product in the near future.