A punctal plug (tear duct plug) is a small medical device that is inserted into the tear duct (puncta) of an eye to block the duct. This prevents the drainage of liquid from the eye. They are used to treat dry eye.
Permanent punctal plugs are usually made of silicone. These are available in various sizes. For maximum effectiveness, the largest size that fits should be used. These are more effective than collagen plugs. They can sometimes become loose and fall out, in which case they can be replaced.
Some plugs are made of thermally reactive material. Some of these are inserted into the punctum as a liquid and then they harden and conform to the individual's drainage system. Others start out rigid and become soft and flexible, adapting to the individual's punctal size after they are inserted.
Artificial tears are usually still required after punctal plug insertion. If punctal plugs are effective, thermal or electric cauterization of puncti can be performed. Such cauterization is relatively permanent and can offer complete closure of the duct, also avoiding the need for a replacement plug when it falls out.
The risks of punctal plugs are fairly small. There is a risk of eye irritation, excessive tearing, and, in rare cases, infection. Some doctors require a disclaimer to be signed prior to the insertion of a plug.
A large silicone plug can cause slight pain upon blinking after insertion. This discomfort may stop within a week.
A systematic review by the Cochrane Collaboration sought to assess the safety and efficacy of punctal plugs for the management of dry eye. The review included seven studies, testing both collagen and silicone plugs. Overall there were mixed results; limited evidence showed that interventions involving permanent silicone or combined silicone/collagen punctal occlusion showed some evidence of clinical efficacy providing symptomatic relief to dry eye.  Some adverse outcomes from participants included spontaneous plug loss, epiphora, ocular irritation, foreign body sensation, and local inflammatory reaction.
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- Ervin AM, Wojciechowski R, Schein O (2010). "Punctal occlusion for dry eye syndrome". Cochrane Database Syst Rev 9: CD006775. doi:10.1002/14651858.CD006775.pub2. PMID 20824852.