What is a Canaliculus?
The canaliculus is a part of the lacrimal apparatus that drains tears from the eyes into the nose. The canaliculus is a channel located on the inner part of the eyelid that moves tears from the eye surface to the lacrimal sac. The canaliculus is an important part of the nasolacrimal drainage system because it allows for tears to exit the eye, flushing out debris in the tears. If the canaliculus is damaged or blocked, then tears are unable to drain properly, and excessive watering of the eyes will occur.
Key Takeaways
- The canaliculus is part of the nasolacrimal drainage system, which drains tears from the surface of the eye into the nasal cavity.
- The tears are routed from the puncta into the canaliculus. The tears then exit the canaliculus and go into the lacrimal sac.
- Blockage of the canaliculus or infection of the canaliculus can cause symptoms such as redness, watering, and discharge from the eyes.
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Understanding Canaliculus
Tears play a significant role in the normal functioning of the eye. They protect the eye, supply oxygen to the cornea, add lubrication between the eyeball and eyelids, and trap debris. The tears drainage mechanism is controlled by the structures present in the lacrimal apparatus, including the canaliculus.
The lacrimal canaliculus is an important component that participates in the tear-drainage system of the lacrimal apparatus. The canaliculi are tubes that join the puncta to the lacrimal sac.
There are two canaliculi channels in each eye. One canaliculus is connected to the upper eyelid punctum, and the other canaliculus is connected to the lower eyelid punctum. The two canaliculi are located in the medial part of the eyelids, close to the nose. The puncta are tiny round openings in the eyelid that drain tears from the surface of the eye. The tears drain into the canaliculus channel through the puncta. While the puncta can be visualized by the naked eye, the canaliculi are underneath the eyelid skin and therefore not visible.
There are two parts of the canaliculus: a vertical aspect and a horizontal aspect. The first portion of the canaliculus is vertical. From the puncta, tears initially drain into the vertical portion of the canaliculus channel. The vertical canaliculus is 2 millimeters long. The canaliculus then turns horizontal to run along the eyelid margin. The horizontal part of the canaliculus is 8 millimeters long. Tears drain from the punctum, into the vertical canaliculus, and then into the horizontal canaliculus. The superior and inferior canaliculi channels meet together and join to form the common canaliculus channel. Tears then exit the common canaliculus into the nasolacrimal sac.
Each canaliculus channel is surrounded by the muscle of Horner, which wraps around and encircles the canaliculus. With every blink, the muscle of Horner contracts, shortening the canaliculus and forcing the canaliculus to drain tears into the lacrimal sac. Thus, with each blink, the canaliculus is drained of tears.
Canaliculus Pathology
Injuries to the canaliculus can affect the tear drainage system. For example, canalicular lacerations are cuts of the eyelid that damage the canaliculus. Canalicular lacerations can occur due to trauma, such as physical injury of the eyes during sports, or from dog bites. Such injury of the canaliculus might adversely affect the tear drainage, resulting in excessive tearing, infection, or inflammation.
Physical blockage of the canaliculus channel can also cause symptoms such as excessive tearing and watering of the eyes. When the canaliculus is physically blocked, the tears are unable to drain to the nasal cavity, and they will often overflow onto the cheek. Someone with perpetual, chronic weepy eyes may be suspected to have a canalicular obstruction.
Canaliculitis is an infection of the canaliculus. The most common pathogen that causes canaliculitis is the Actinomyces israelii bacteria. Although canaliculitis is rare, it can cause symptoms such as red eye, watery eyes, and yellow discharge.
