The lacrimal punctum is a minute component of the eye’s anatomy that serves a major function in maintaining ocular surface health. This small opening acts as the primary gateway for the continuous removal of tears from the eye’s surface. The punctum is part of the nasolacrimal system, which is the entire drainage apparatus responsible for recycling tear fluid. Without its proper function, tears would accumulate and spill over, leading to discomfort and vision disruption.
Where the Punctum is Located
The punctum, which is the singular term, is found on the inner edge of both the upper and lower eyelids. There are two distinct openings, one superior and one inferior, positioned closest to the nose at the inner corner of the eye, known as the medial canthus. These openings are typically minute, measuring approximately 0.2 to 0.3 millimeters in diameter, making them barely visible without magnification.
The superior and inferior puncta sit atop a slight elevation of tissue called the lacrimal papilla. They are angled inward toward the eye’s surface, specifically dipping into the tear meniscus, which is the small pool of tears that collects along the eyelid margin. The two openings are not perfectly aligned; the inferior punctum is situated slightly more lateral—about 0.5 millimeters—than the superior punctum. Each punctum opens directly into a small channel called a canaliculus, which begins the deeper journey of the tear drainage system.
How the Punctum Facilitates Tear Drainage
The punctum functions as the initial collection point, relying on a combination of physics and muscle action to move tears. Tears are first drawn into the small opening through a natural process called capillary action, which is the ability of a liquid to flow in narrow spaces against the force of gravity. This process draws the tear fluid from the eye’s surface into the initial vertical portion of the canaliculus.
The more significant force, however, is generated by the “lacrimal pump mechanism,” which is activated during a blink. The orbicularis oculi muscle, which is the muscle surrounding the eye, plays a direct role in this pumping action. As the eyelids close, the muscle contracts, which squeezes the canaliculi and shortens the length of the system. Simultaneously, the contraction of the muscle around the tear sac creates a negative pressure inside the sac.
This negative pressure acts like a vacuum, actively pulling the tears from the eye’s surface, through the punctum, and into the lacrimal sac. As the blink cycle completes and the eye opens, the muscle relaxes, and the resulting positive pressure forces the collected tears onward. The fluid is then propelled down the nasolacrimal duct and into the nasal cavity, which is why crying often leads to a runny nose.
When the Punctum Causes Problems
Dysfunction of the punctum typically results in epiphora, the medical term for persistent, excessive tear overflow onto the cheek. This occurs when the punctum fails to collect tears efficiently, disrupting the delicate balance of tear production and drainage. The most common issue affecting the punctum directly is stenosis, which is the abnormal narrowing of the opening.
Punctal stenosis can be caused by chronic inflammation, such as long-term blepharitis, or by the side effects of certain medications, including some topical anti-glaucoma drops or systemic chemotherapy agents. If the opening narrows significantly or becomes completely occluded, the entry point into the drainage system is blocked, causing tears to pool and spill. Another functional problem arises from eyelid malposition, such as ectropion, where the eyelid margin rolls outward, pulling the punctum away from the tear lake.
When the punctum is not properly positioned against the eye, it cannot engage the tear film, rendering the entire drainage mechanism ineffective. Treatment for stenosis often involves a minor procedure called punctoplasty or dilation, which aims to surgically widen the constricted opening and restore the proper flow. Conversely, in cases of severe dry eye, tiny devices called punctal plugs may be temporarily or permanently inserted into the punctum to intentionally block drainage, helping to retain the eye’s natural tears on the surface.