The small opening on the edge of your eyelid, often called the “little hole on your waterline,” is a normal part of your eye’s anatomy. This feature is medically known as the lacrimal punctum, and it is the starting point of your eye’s tear drainage system. Your eyes constantly produce a tear film for lubrication, protection, and nourishment. This tiny hole acts as a drain for this fluid, preventing tears from continuously spilling over onto your cheek.
Identifying the Punctum and Canaliculi
The punctum is a small opening located near the inner corner of your eye, which is the area referred to as the medial canthus. You have four of these openings in total: one on the margin of your upper eyelid and one on the margin of your lower eyelid for each eye. These openings sit directly on the “waterline,” or the eyelid margin, and are angled slightly toward the eye’s surface to collect tears.
The singular term is “punctum,” while “puncta” is the plural term for the pair in each eye. Each punctum leads immediately into a tiny tube called a canaliculus. These canaliculi are the next segment of the drainage pathway, running first vertically for about two millimeters and then horizontally before joining together.
The entire structure, including the punctum and the canaliculus, is engineered to be a precise collection point. Tears pool in the lacrimal lake, the small reservoir of tear fluid that collects at the inner corner of the eye. The puncta dip into this lake to begin the process of draining away the used tear fluid.
The Role of the Punctum in Tear Drainage
The punctum serves as the initial drain for the tears that constantly bathe the surface of the eye. Tears are produced by the lacrimal gland, located above the outer corner of the eye, and are then spread across the eye with every blink. The fluid then moves toward the inner corner, where the puncta are located.
This drainage is an active mechanism known as the lacrimal pump. Every time you blink, the muscles around the eyelids compress the tear drainage system, creating a negative pressure that actively sucks tears from the eye’s surface into the punctum and down the canaliculus. This mechanical action is highly efficient at removing excess fluid and maintaining a stable tear film.
The punctum must be positioned correctly to interact with the tear fluid pooled along the eyelid margin. If the punctum is not correctly aligned, or if the eyelid is too loose, the lacrimal pump mechanism may fail to collect the tears efficiently. This can result in tears overflowing onto the cheek, a condition known as epiphora.
Where Tears Go Next: The Nasolacrimal Duct System
Once tears pass through the punctum and the connecting canaliculi, they enter the next stage of the drainage pathway. The two canaliculi, one from the upper lid and one from the lower, typically merge into a common canaliculus before emptying into the lacrimal sac. The lacrimal sac is a small reservoir situated on the side of the nose, just beneath the skin.
From the lacrimal sac, the tears continue their journey downward through the nasolacrimal duct. This duct is a tube that travels through a bony canal and empties directly into the nasal cavity beneath the inferior turbinate. The entire pathway from the punctum to the nose is called the nasolacrimal duct system.
The destination of the tears explains why crying causes a runny nose; the excess fluid is draining into the nasal passage. Tears that reach the nasal cavity are either reabsorbed by the body, swallowed, or expelled. This connection is also why you can sometimes taste eye drops, as the medication drains down the same internal route.
When the System Fails: Blockages and Related Issues
When any part of this drainage system is obstructed, the result is often excessive tearing, or epiphora. This blockage can occur anywhere from the punctum itself to the nasolacrimal duct. Symptoms can include blurry vision and skin irritation on the eyelids from constant wiping.
A specific problem that can arise is dacryocystitis, which is an infection or inflammation of the lacrimal sac. This condition is usually caused by a blockage in the nasolacrimal duct, which allows tears to stagnate in the sac. Acute dacryocystitis can present with pain, swelling, and redness over the inner corner of the eye, and sometimes a thick discharge may be squeezed out through the punctum.
In contrast to blockages, the punctum is sometimes intentionally blocked as a medical treatment for dry eye syndrome. Tiny devices called punctal plugs are inserted into the puncta to reduce the outflow of tears. By keeping the eye’s natural lubrication on the surface longer, these plugs help maintain a healthier tear film and alleviate dry eye symptoms. These plugs can be temporary (dissolvable collagen) or semi-permanent (typically made of silicone).