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By implanting a punctal plug in both the superior and inferior punta-literally, plugging the drains-clinicians can reduce tear turnover rate via these ducts. Reducing nasolacrimal drainage is one way of increasing tear volume on the ocular surface, in the hopes of prolonging the residence time of the tear film, and thus improving the signs and symptoms of dry eye.
Dry eye is a complex disease with many underlying causes and influential factors, including environmental conditions, visual tasking, systemic medications (e.g., antihistamines), and autoimmune disease.
One of the primary functions of blinking is to spread the tear film across the ocular surface, providing a protective barrier from the external environment. Under normal conditions, after the tear film is spread with a blink, the tears are drawn into the puncta, flow into the canaliculi, and then to the lacrimal sac, nasolacrimal duct, and finally drain into the nose.1 In patients with dry eye, the tear film is unstable due to an alteration in the quality or quantity of any one of the tear film components: mucin, lipids, or aqueous. In addition, tear drainage in patients with dry eye may result in insufficient ocular surface protection between blinks.2
One dry eye treatment aims to counteract this drainage directly. By implanting punctal plugs in both the superior and inferior puncta-literally, plugging the drains-clinicians can reduce tear turnover rate. Reducing nasolacrimal drainage is one way of increasing tear volume on the ocular surface, in the hope of prolonging the residence time of the tear film, and thus improving the signs and symptoms of dry eye.
If a patient demonstrates mild clinical signs and/or symptoms of dry eye, the clinician's first line of therapy typically is to prescribe artificial tears. If these prove ineffective, or the patient is using the tears so frequently that it becomes inconvenient, punctal plugs may be the next course of action.
Punctal plugs can be temporary, typically dissolving in anywhere from days to months, or permanent, such as silicone plugs. Insertion techniques also can vary by design, ranging from requiring a clinician to examine the puncta in order to identify the ideal plug size or involving "one-size-fits-all," labile designs that eliminate the need for measurement. Often, a dissolvable plug is used initially to determine patient satisfaction and effectiveness of occlusion therapy. If dry eye symptoms and/or signs improve, a permanent plug can be used for longer-term relief.3
Differences in plugs
For years, silicone punctal plugs have been the most popular choice for permanent occlusion. In rare cases, however, silicone plugs have caused complications such as unplanned extrusion of the plugs and the formation of pyogenic granulomas.4 Newer plug designs have lowered the risk of these complications, and the latest research in punctal plug design demonstrates interesting results.
One recent study compared a thermosensitive hydrophobic acrylic plug (SmartPlug, Medennium) with a conventional silicone plug. The acrylic plug is an adaptable design that is solid at room temperature but turns to gel upon insertion to expand in the punctum.
Thirty-six eyes were randomly selected to receive one of the punctal plugs, which was inserted in the inferior punctum. Although no between-group differences were noted for improvements in tear film break-up time, symptom scores, and ocular surface staining, acrylic plug-treated eyes showed significant improvement in mean tear meniscus height when compared with the silicone plugs, and exactly half of minor complications resulted from implantation of the acrylic plugs versus silicone plugs.
Finally, although 33% of the silicone punctal plugs were spontaneously lost during normal, everyday activity, none of the acrylic plugs was lost.5
Findings reported at this year's Association for Research in Vision and Ophthalmology meeting demonstrated a preliminary step toward the next generation of permanent punctal occlusion. Researchers presented findings on a newly developed biodegradable plug that releases basic fibroblast growth factor in order to induce growth of connective tissue in the lacrimal canaliculi. Gradually degrading over time, the plugs appeared successful in inducing connective tissue growth in rabbit canaliculi.6