The lacus lacrimalis, also known as the tear lake, is a small pool of tears that accumulates in the medial canthus (inner corner) of the eye. This small reservoir holds excess tears after they have been spread across the surface of the eye by blinking. The lacus lacrimalis serves as a temporary collection point for tears before they enter the tear drainage system through the lacrimal puncta.
Location
The lacus lacrimalis is located at the medial canthus of the eye, between the inner edges of the upper and lower eyelids, near the lacrimal caruncle (a small pink, fleshy area at the inner corner of the eye). It sits adjacent to the lacrimal puncta, which drain tears into the lacrimal canaliculi. The tear lake occupies a small space near the junction of the eyelids and the nose.
Structure and Anatomy
The lacus lacrimalis, or tear lake, is an important anatomical structure involved in the tear drainage system. It acts as a small reservoir for excess tears at the inner corner of the eye before they are drained into the lacrimal puncta and the tear drainage system. Below is a detailed description of its anatomy.
Size and Shape
The lacus lacrimalis is a small, crescent-shaped or triangular pool of fluid that forms in the depression between the eyelids at the medial canthus. Its size is generally small, depending on the volume of tears present, but it can expand slightly during times of increased tear production, such as crying or eye irritation.
Tear Volume: The size of the tear lake can vary based on the rate of tear production and drainage. Under normal conditions, the tear lake contains a small, stable volume of fluid that is continuously refreshed by tear production and drainage.
Composition
The lacus lacrimalis contains the same three layers that make up the tear film: the lipid (outer) layer, the aqueous (middle) layer, and the mucin (inner) layer. Together, these layers help maintain the health of the ocular surface and prevent the tear lake from evaporating too quickly.
- Lipid Layer: Produced by the meibomian glands, this outermost layer helps prevent the tears from evaporating too quickly and maintains the tear lake’s stability.
- Aqueous Layer: The middle, watery layer of the tear film, produced by the lacrimal glands, provides hydration and contains proteins and electrolytes that nourish the eye.
- Mucin Layer: The innermost layer, produced by goblet cells in the conjunctiva, helps tears adhere to the surface of the eye and contributes to the tear film’s uniform distribution.
Relationship with Adjacent Structures
The lacus lacrimalis is closely associated with several anatomical structures involved in tear drainage and ocular surface maintenance:
- Lacrimal Puncta: The superior and inferior lacrimal puncta are small openings located near the medial canthus, directly adjacent to the tear lake. These puncta serve as the entry points for tears into the lacrimal canaliculi, draining tears from the lacus lacrimalis.
- Lacrimal Caruncle: A small, fleshy, pink mound located in the medial canthus, just adjacent to the tear lake. The lacrimal caruncle contains sebaceous and sweat glands and plays a minor role in maintaining the tear film.
- Plica Semilunaris: A crescent-shaped fold of the conjunctiva located next to the tear lake, near the lacrimal caruncle. The plica semilunaris allows for greater mobility of the eye and is also involved in tear film maintenance.
Blood Supply
The blood supply to the area surrounding the lacus lacrimalis is provided by branches of the ophthalmic artery and the facial artery. These arteries supply blood to the medial aspect of the eyelids and the structures involved in tear drainage:
- Ophthalmic Artery: A branch of the internal carotid artery, supplying the eyelids and lacrimal apparatus, including the medial canthus and tear drainage system.
- Facial Artery: Provides additional blood supply to the medial portion of the eyelids and surrounding tissues.
Innervation
The lacus lacrimalis is innervated by sensory nerves, primarily from branches of the trigeminal nerve (cranial nerve V), which provides sensation to the eyelids and adjacent structures:
Infratrochlear Nerve: A branch of the ophthalmic division of the trigeminal nerve that innervates the medial portion of the eyelids, including the region around the tear lake.
This sensory innervation is important for detecting any sensations of irritation or blockage in the tear drainage system.
Lymphatic Drainage
The lymphatic drainage from the area surrounding the lacus lacrimalis is directed toward the submandibular lymph nodes. These lymph nodes help manage the drainage of excess fluid and waste products from the medial portion of the eye and the lacrimal system.
Relationship with the Tear Meniscus
The lacus lacrimalis is closely connected with the tear meniscus, a thin strip of tear fluid that forms along the eyelid margins. The tear meniscus runs along the edge of the upper and lower eyelids and helps funnel tears toward the medial canthus, where they accumulate in the tear lake.
Tear Flow: As tears are spread across the surface of the eye during blinking, they collect in the tear meniscus and flow toward the medial canthus, where they pool in the lacus lacrimalis before entering the lacrimal puncta for drainage.
Function
The lacus lacrimalis (tear lake) plays a vital role in the tear drainage system and the maintenance of a healthy ocular surface. Although small, it is an essential part of the lacrimal apparatus, ensuring that tears are collected, stored temporarily, and directed into the tear drainage system. Below is a detailed explanation of the functions of the lacus lacrimalis.
Collection of Tears
The primary function of the lacus lacrimalis is to collect excess tears that are produced by the lacrimal glands and spread across the surface of the eye during blinking. Tears are necessary to maintain eye moisture, flush away debris, and protect the eye from infection. After tears are distributed over the surface of the eye, they accumulate in the tear lake at the medial canthus.
Tear Reservoir: The lacus lacrimalis serves as a small reservoir where tears accumulate after they have fulfilled their protective role on the eye’s surface. This collection of tears is essential for ensuring a smooth flow into the tear drainage system via the lacrimal puncta.
Temporary Storage of Tears
The lacus lacrimalis acts as a temporary holding area for tears before they are drained. Tears remain in the tear lake briefly before being funneled into the lacrimal puncta and subsequently into the lacrimal canaliculi. This temporary storage ensures that there is no overflow of tears onto the face (which would cause excessive tearing or epiphora).
Balancing Tear Flow: By storing tears temporarily, the tear lake helps maintain a balance between tear production and drainage. This function is especially important in regulating tear flow during times of increased tear production, such as crying or exposure to irritants.
Facilitation of Tear Drainage
The lacus lacrimalis plays a crucial role in guiding tears into the tear drainage system. Tears are funneled from the tear lake into the nearby lacrimal puncta, small openings located in the upper and lower eyelids. From there, the tears enter the lacrimal canaliculi and are eventually drained into the lacrimal sac and nasolacrimal duct.
Efficient Tear Flow: The tear lake is positioned strategically at the medial canthus, close to the lacrimal puncta. Its proximity to the puncta ensures that tears are directed efficiently into the tear drainage system, preventing excess tears from remaining on the eye’s surface.
Prevention of Tear Overflow
By serving as a collection and drainage point for tears, the lacus lacrimalis helps prevent the buildup of excess tears on the surface of the eye, a condition known as epiphora (excessive tearing). The tear lake collects and funnels tears into the drainage system, preventing them from spilling over the eyelids and onto the face.
Managing Tear Volume: When tear production is normal, the lacus lacrimalis ensures that tears are drained at a steady rate, preventing overflow. When tear production increases, such as during crying, the tear lake expands slightly to accommodate the excess fluid before draining it through the lacrimal system.
Maintenance of Tear Film Stability
The lacus lacrimalis helps in maintaining the stability of the tear film by regulating the flow of tears across the ocular surface. The tear film, which covers the surface of the eye, is essential for protecting the eye from infection, nourishing the cornea, and keeping the eye’s surface smooth for clear vision.
Tear Film Balance: By collecting excess tears, the tear lake helps maintain the proper balance of the tear film. It prevents the eye from becoming too wet (due to excessive tear retention) or too dry (due to insufficient tear collection), both of which can compromise the health of the cornea and conjunctiva.
Participation in Eye Cleansing
The tears that accumulate in the lacus lacrimalis contain not only moisture but also substances that cleanse the eye of debris, dust, and microorganisms. As tears are collected in the tear lake, these impurities are directed toward the tear drainage system, helping to keep the eye’s surface clean.
Removal of Debris: The tear lake plays a role in removing small particles and debris from the surface of the eye. Tears carry these foreign substances to the tear lake, where they can be drained through the puncta and lacrimal drainage system.
Response to Increased Tear Production
During times of increased tear production, such as crying or eye irritation, the lacus lacrimalis serves as an expanded reservoir for the larger volume of tears. This helps manage the higher tear flow and ensures that the tears can still be directed into the drainage system without spilling excessively over the eyelids.
Adapting to Tear Volume: The tear lake’s ability to accommodate increased tear volume is important for managing fluctuations in tear production. During emotional crying or exposure to irritants, the tear lake prevents tears from overflowing onto the face by expanding slightly and allowing for efficient drainage.
Interaction with the Tear Meniscus
The lacus lacrimalis is closely associated with the tear meniscus, the thin strip of tear fluid that forms along the margins of the upper and lower eyelids. The tear meniscus helps guide tears toward the medial canthus, where they pool in the tear lake. The interaction between the tear meniscus and the tear lake ensures that tears are efficiently funneled into the drainage system.
Guiding Tears to the Lake: The tear meniscus plays a key role in directing tears toward the tear lake. As tears move along the edges of the eyelids, they are collected in the tear lake for eventual drainage into the lacrimal puncta.
Clinical Significance
The lacus lacrimalis plays a crucial role in the tear drainage system, and any issues related to it can lead to clinical concerns:
- Epiphora (Excessive Tearing): Dysfunction in tear drainage from the lacus lacrimalis can lead to epiphora, where excess tears overflow onto the cheeks. This can occur due to blockage of the lacrimal puncta, canaliculi, or nasolacrimal duct.
- Tear Drainage Obstruction: Obstruction at any point in the lacrimal drainage system can cause tears to accumulate in the tear lake, resulting in discomfort, blurred vision, or infection.
- Infections and Inflammation: Conditions such as dacryocystitis (infection of the lacrimal sac) can cause inflammation and swelling around the medial canthus, affecting the tear lake and tear drainage.
