Kollyrion (κολλύριον) refers to eye salve — medicinal ointment applied to the eyes to improve vision. It appears only in Revelation 3:18, where Christ addresses the lukewarm church at Laodicea: 'Buy from me gold refined in the fire... and salve [kollyrion] to put on your eyes, so you can see.' Laodicea was famous for its actual eye medicine, making the metaphor pointed and local.
The Laodicean church thought it was rich and had need of nothing — but Christ diagnosed them as 'blind.' The prescription is kollyrion — spiritual eye salve from Christ Himself. The same Laodicea that sold physical eye medicine to the ancient world needed to admit its spiritual blindness and seek the true cure. This is one of Scripture's most effective uses of local imagery to drive home a spiritual point: your famous medicine cannot fix the blindness of self-sufficiency.
Laodicea lay in the Lycus valley near Hierapolis, whose spring waters were lukewarm when they reached Laodicea — neither hot (healing) nor cold (refreshing). The city was also known for Phrygian powder, a famous eye medicine. Christ uses BOTH local realities: 'You are lukewarm like your water, and you are blind despite your eye medicine.' The cure for Laodicean blindness is not their own medicine but Christ's — the kollyrion of repentance and relationship.