Tear Film: Structure and Functions

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Questions and Answers

What is the primary function of the outer lipid layer of the tear film?

To prevent contamination from particles and microorganisms (correct)

To increase friction during blinking

To provide nutrients to the cornea

To promote pathogen adhesion to the ocular epithelium

Which type of gland is responsible for secreting the central aqueous layer of the tear film?

Lacrimal gland (correct)

Goblet cell

Meibomian gland

Sebaceous gland

What is the main function of the inner mucin layer of the tear film?

To reduce friction during blinking (correct)

To nourish the avascular cornea

To promote pathogen adhesion to the ocular epithelium

To increase evaporation of tears

Where are the meibomian glands located?

In the tarsal plates of the upper and lower eyelids Signup and view all the answers

What is the function of the tear film in relation to the avascular cornea?

To nourish the cornea with oxygen, proteins, and salts Signup and view all the answers

What type of gland is a goblet cell?

Unicellular exocrine gland Signup and view all the answers

What is the location of the conjunctiva?

Posterior surface of the eyelid and the exposed surface of the eyeball up to the limbus Signup and view all the answers

How many components does the tear film have?

3 Signup and view all the answers

What is the first thing that light rays encounter when they impinge on the surface of the eye?

The tear film Signup and view all the answers

What is the approximate volume of the tear film?

7 µl Signup and view all the answers

What is one of the functions of the tear film?

To lubricate the eye Signup and view all the answers

What is the tear film composed of?

A sophisticated mix of mucous, serous, and sebaceous substances Signup and view all the answers

What is another function of the tear film?

To maintain the health of underlying epithelial cells Signup and view all the answers

What is the tear film responsible for ensuring in terms of vision?

A smooth refractive surface Signup and view all the answers

What type of secretions do tarsal glands produce?

Sebaceous secretions Signup and view all the answers

Which muscle is responsible for raising the upper eyelid?

Levator palpebrae superioris Signup and view all the answers

What happens to the tears when the orbicularis oculi muscle contracts?

They are drawn from the tear film Signup and view all the answers

What type of muscle is the superior tarsal muscle?

Smooth muscle Signup and view all the answers

What is the purpose of blinking in relation to the tear film?

To distribute the tear film over the ocular surface Signup and view all the answers

Which glands produce mucous secretions that contribute to the tear film?

Conjunctival goblet cells Signup and view all the answers

What is the role of the orbicularis oculi muscle in relation to the eye?

To close the palpebral aperture Signup and view all the answers

What type of secretions do lacrimal glands produce?

Serous secretions Signup and view all the answers

Study Notes

Tear Film

The tear film is the first thing light rays encounter when they impinge on the surface of the eye.
It is a thin layer (~7 µl) of fluid with multiple functions, including: • Lubricating the eye • Acting as a barrier to foreign bodies and pathogens • Maintaining the health of underlying epithelial cells • Ensuring a smooth refractive surface for vision
The tear film is composed of a sophisticated mix of mucous, serous, and sebaceous substances, arranged in layers.

Outer Lipid Layer (Sebaceous)

The outer lipid layer has various roles, including: • Minimizing evaporation • Limiting contamination from particles and microorganisms • Increasing surface tension (stops tears from overflowing onto the skin)
It is secreted primarily by meibomian (“tarsal”) glands, located within tarsal plates of upper and lower eyelids.
These glands are simple, multicellular exocrine glands with one duct and multiple secretory units.

Central Aqueous Layer (Serous)

The central aqueous layer has various roles, including: • Washing away foreign bodies and contaminations • Nourishing the avascular cornea (oxygen, proteins, salts)
It is secreted primarily by the lacrimal gland, located above the upper eyelid.
The lacrimal gland is a compound multicellular exocrine gland with multiple ducts.

Inner Mucin Layer (Mucous)

The inner mucin layer has various roles, including: • Forming a glycocalyx over the ocular epithelium that prevents pathogen adhesion • Reducing friction during blinking
It is secreted by goblet cells, located in the conjunctiva (a mucous membrane covering the posterior surface of the eyelid and the exposed surface of the eyeball up to the limbus).
Goblet cells are unicellular exocrine glands with a distinctive triangular nucleus.

Tear Film Summary

The tear film covers the anterior (front) surface of the eye.
It has many important roles and is composed of three components: • Sebaceous secretions (tarsal glands) • Serous secretions (lacrimal gland) • Mucous secretions (conjunctival goblet cells)
Blinking is required to distribute the tear film over the ocular surface.

Blinking

Two skeletal muscles are involved in opening and closing the eye: • The orbicularis oculi, which runs in concentric bands around the eye • The levator palpebrae superioris, which raises the upper eyelid
Other muscles are also involved, including the superior tarsal muscle, which is a smooth muscle that helps to raise the upper eyelid.

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Description

Learn about the tear film, a thin layer of fluid on the eye's surface, and its multiple functions, including lubrication, protection, and maintaining a smooth refractive surface for vision.