Wearing an eye represents having a watchful eye always open to watch and protect the wearer against evil eye - or Ayin Hara a concept in Jewish tradition. Ayin Ha'ra in Hebrew means "evil eye''. In Hebrew people say "Ble Ayin Ha'ra". "Away Evil Eye" to someone.
The term "Hamsa Alek", in Judeo-Arabic, has the same loose meaning as "Bli Ayin Ha'ra". The concept of negative energy is what is meant when we use the term 'evil eye". Being jealous or envious, someone giving you bad vibes. It can happen these days with social media especially. We can use all the spirtual protection we can get. These ancient symbols used in talismans and amulets have a symbolic property that our Kabbalistic mystical teachings tell us. Kabbalah is the mystical teachings of Judiasm. The heavy, mind blowing physics stuff that tells us about the nature of the Universe. It's like physics and spiritually all in one.
These teachers used these symbols and concepts then and we are still connected to them thousands of years later.