Page 59 in PS 788 (Jul 18) talked about the importance of replacing missing parts on the AN/ PVS-14 monocular night vision device (MNVD). That includes the eyeguard, NSN 6650-01-444- 1229.
One reader thought the part should have referred to the eyeshield (commonly called eyecup), NSN 5855-01-246-8273, since the article showed a helmet-mounted AN/PVS-14.
The eyecup, which is not a component of end item (COEI), is only used with the helmet-mounted version.
The eyeguard, which is COEI, is used with the weapon-mounted version.
Both parts are essential to maintain light security and prevent detection by the enemy. If either is missing, replace them ASAP.