The lacrimal punctum is a small opening located on the inner edges of both the upper and lower eyelids. It serves as the entry point for tears into the tear drainage system, specifically into the lacrimal canaliculi, which transport tears to the lacrimal sac and ultimately to the nasal cavity. Each eye has two lacrimal puncta: one in the upper eyelid (superior punctum) and one in the lower eyelid (inferior punctum). These openings are essential for the proper drainage of tears from the eye’s surface.
Location
The lacrimal punctum is located near the medial canthus (inner corner) of the eye, on both the upper and lower eyelid margins. The superior punctum is situated on the inner edge of the upper eyelid, while the inferior punctum is located on the inner edge of the lower eyelid. Both puncta are positioned adjacent to the tear lake, the small pool of tears that collects at the inner corner of the eye. They are aligned near the lacrimal canaliculi, which they drain into for tear removal.
Structure and Anatomy
The lacrimal punctum is an essential component of the lacrimal drainage system. It consists of small openings that serve as the entry point for tears from the eye’s surface into the lacrimal canaliculi. Each eye has two puncta: one in the upper eyelid and one in the lower eyelid. Below is a detailed description of the lacrimal punctum’s anatomy.
Number and Location
Each eye has two lacrimal puncta:
- Superior Lacrimal Punctum: Located on the upper eyelid.
- Inferior Lacrimal Punctum: Located on the lower eyelid.
These puncta are positioned at the junction of the eyelids near the medial canthus (inner corner of the eye). They are situated on the medial (inner) side of both the upper and lower eyelids, close to the eyelashes, and are aligned with the lacrimal canaliculi, which transport tears toward the lacrimal sac.
Size and Shape
The lacrimal punctum is a small, round or slightly oval-shaped opening that measures approximately 0.3 to 0.5 mm in diameter. These puncta are visible to the naked eye but may require magnification for detailed examination. They appear as tiny pits or holes on the eyelid margins and serve as gateways for tear drainage.
Structural Composition
The lacrimal punctum is composed of epithelial tissue that lines its inner surface. This epithelial lining is continuous with the conjunctiva and skin of the eyelids and extends into the lacrimal canaliculi, maintaining a smooth pathway for tear drainage. The tissue surrounding the punctum provides structural support to ensure that the opening remains patent (open) and functional.
- Epithelial Lining: The inner surface of the punctum is lined with stratified squamous epithelium, similar to the surrounding skin and conjunctiva.
- Surrounding Tissue: The punctum is supported by fibrous tissue within the eyelid, which helps maintain its shape and prevent collapse.
Orientation and Alignment
The lacrimal puncta are oriented to face slightly toward the tear lake (the small pool of tears that collects at the medial canthus). This orientation allows them to capture tears effectively and direct them into the lacrimal canaliculi for drainage. Both the superior and inferior puncta are positioned near the tear meniscus, the thin film of tears that borders the edge of the eyelid.
Tear Meniscus: The puncta are positioned to interact with the tear meniscus, a small reservoir of tears along the eyelid margin. The meniscus helps funnel tears into the puncta for drainage.
Relationships with Adjacent Structures
The lacrimal punctum is closely related to several important anatomical structures in the eye:
- Medial Canthus: The inner corner of the eye where the upper and lower eyelids meet. The puncta are located just adjacent to this area, allowing for optimal tear collection.
- Lacrimal Canaliculi: The superior and inferior puncta are directly connected to the lacrimal canaliculi, which begin at the puncta and extend medially toward the lacrimal sac. The canaliculi transport tears from the puncta to the lacrimal sac.
- Tear Lake (Lacus Lacrimalis): The puncta are situated near the tear lake, a small pool of tears that accumulates at the medial canthus. The tear lake acts as a reservoir of tears that are collected by the puncta for drainage.
Blood Supply
The blood supply to the lacrimal puncta is derived from branches of the ophthalmic artery and the facial artery:
- Ophthalmic Artery: A branch of the internal carotid artery, which supplies the eyelids and adjacent structures, including the lacrimal puncta.
- Facial Artery: Provides additional blood supply to the medial canthus and the surrounding tissues of the punctum.
Innervation
The lacrimal punctum receives sensory innervation from the branches of the trigeminal nerve (cranial nerve V), which provides sensation to the eyelids and adjacent areas:
Infratrochlear Nerve: A branch of the ophthalmic division of the trigeminal nerve that supplies the medial portion of the eyelids and the punctum.
This sensory innervation ensures that any irritation or obstruction of the punctum can be detected and triggers the appropriate response, such as reflex tearing.
Lymphatic Drainage
The lymphatic drainage of the lacrimal puncta is directed to the submandibular lymph nodes, which help manage excess fluid and waste from the surrounding tissues, ensuring that the area remains free from infection and inflammation.
Function
The lacrimal punctum plays a crucial role in the tear drainage system, serving as the entry point for tears into the lacrimal drainage pathway. Its proper function ensures that tears are efficiently collected and drained away from the surface of the eye, preventing tear buildup and maintaining clear vision. Below are the detailed functions of the lacrimal punctum:
Tear Collection
The primary function of the lacrimal punctum is to collect tears from the surface of the eye. Tears are produced by the lacrimal glands and spread across the eye during blinking to keep the eye moist and free from debris. After spreading across the eye, excess tears accumulate at the tear lake (lacus lacrimalis), a small pool of tears located near the inner corner of the eye (medial canthus).
Tear Entry Point: The lacrimal puncta act as small openings that allow tears from the tear lake to enter the lacrimal drainage system. The superior and inferior puncta, located on the upper and lower eyelid margins respectively, capture tears at the edge of the tear meniscus (a thin layer of tears along the eyelid margin).
Directing Tears into the Lacrimal Canaliculi
Once tears are collected by the lacrimal puncta, they are directed into the lacrimal canaliculi, small ducts that transport tears to the lacrimal sac. The puncta ensure that the flow of tears is effectively transferred from the eye surface into the canaliculi without any loss.
Connection to Lacrimal Canaliculi: The lacrimal puncta are directly connected to the lacrimal canaliculi. The superior punctum drains tears into the superior canaliculus, while the inferior punctum drains tears into the inferior canaliculus. These two canaliculi typically unite to form a common canaliculus before draining into the lacrimal sac.
Tear Regulation
The lacrimal punctum helps regulate the volume of tears on the eye’s surface by controlling the amount of fluid that enters the tear drainage system. By efficiently draining tears, the puncta prevent excessive tear buildup (which could cause the tears to spill onto the face) or tear deficiency (which could lead to dry eye).
Dynamic Tear Balance: During normal tear production, the puncta maintain a balance between tear production and drainage, ensuring that the eye remains adequately lubricated without overflow. When tear production increases, such as during crying or irritation, the puncta adjust by allowing more tears to drain.
Preventing Tear Overflow (Epiphora)
One of the key functions of the lacrimal punctum is to prevent epiphora (excessive tearing or tear overflow). By continuously draining tears from the eye’s surface, the puncta help maintain a stable tear film and prevent tears from spilling over the eyelid margins onto the face.
Epiphora Prevention: Proper functioning of the puncta ensures that the tears are efficiently drained into the lacrimal system. If the puncta become blocked or malfunction, tears may overflow onto the face, resulting in epiphora. Therefore, the puncta play an essential role in keeping the eye’s surface clear of excess tears.
Coordination with Blinking
The lacrimal punctum works in coordination with the blinking mechanism to optimize tear drainage. During each blink, the eyelids come into contact with the tear film on the surface of the eye. This action helps guide tears toward the medial canthus, where they can be collected by the puncta.
Blinking Action: Blinking compresses the tear film and moves tears medially toward the lacrimal puncta. The force generated by blinking helps funnel tears into the puncta, ensuring that they are captured and directed into the lacrimal canaliculi for drainage.
Maintenance of Tear Film Stability
The lacrimal puncta contribute to maintaining the stability and composition of the tear film on the eye’s surface. By draining excess tears, they help ensure that the tear film is regularly replenished and remains in balance. A stable tear film is essential for protecting the eye from environmental debris, microorganisms, and drying.
Tear Film Regulation: The puncta help regulate the flow of tears, which in turn maintains the stability of the tear film. This prevents the accumulation of stale or excess tears, ensuring that the tear film remains fresh and functional.
Response to Increased Tear Production
In situations where tear production is elevated, such as during emotional crying, eye irritation, or exposure to irritants like wind or smoke, the lacrimal puncta adapt by draining the excess tears more rapidly. This helps prevent excessive tear buildup on the eye’s surface.
Adaptation to Tear Volume: The lacrimal puncta can accommodate increased tear production by increasing the rate of tear drainage. This ability helps manage fluctuations in tear volume, preventing excessive tear retention on the eye’s surface.
Clinical Significance
The lacrimal punctum is essential for the proper drainage of tears, and any dysfunction or blockage can lead to various clinical issues:
- Punctal Stenosis: This condition refers to the narrowing or complete blockage of the lacrimal punctum, which can impair tear drainage and result in epiphora (excessive tearing). Punctal stenosis may be caused by aging, inflammation, chronic eye infections, or trauma.
- Punctal Occlusion: In certain cases, punctal occlusion is performed intentionally as a treatment for dry eye syndrome. Small plugs (punctal plugs) are inserted into the punctum to reduce tear drainage and increase moisture on the eye surface.
- Infection or Inflammation: Blockage or infection of the lacrimal punctum can lead to inflammation, resulting in irritation, redness, and tearing.
