What are the main functions of the eyelids?
- Protection – They shield the globe from light, foreign bodies, and mechanical damage.
- Tear production – They help in the production and secretion of various components of the tear film.
- Tear distribution – They spread tears evenly over the ocular surface during blinking.
What is the palpebral aperture?
It is the opening between the upper and lower eyelids, allowing light to enter the eye.
What is the canthus and what are its two types?
The canthus refers to the angles formed at the medial and lateral ends of the palpebral aperture — the medial canthus (near the nose) and the lateral canthus (toward the temple).
What is the superior palpebral sulcus?
A fold that separates the orbital part of the eyelid from the tarsal part, contributing to eyelid contour.
What is the function of the eyebrow?
The eyebrow marks the upper boundary of the orbital eyelid, prevents sweat and moisture from entering the palpebral aperture, and plays an important role in facial expression.
What is the epicanthus?
A medial fold of skin that partially covers the sclera, often seen near the inner canthus.
What is the caruncula lacrimalis?
A small, fleshy pad of tissue located on the medial side of the eye between the eyelids; it contains sweat and sebaceous glands.
What are puncta (singular: punctum)?
The small openings located on the papilla lacrimalis that serve as the entry points to the nasolacrimal drainage system, allowing tears to drain from the eye surface.
How many layers make up the eyelid?
5-6 layers
Describe the structure of eyelid skin.
The eyelid skin is thin and loosely attached to underlying muscle, making it flexible and susceptible to swelling or bruising.
What happens to the eyelid’s potential space during trauma?
It can fill with blood due to its loose attachment, causing eyelid edema or hematoma.
What is the lifespan of eyelashes, and do they regenerate?
Eyelashes last about 3–5 months and regenerate quickly after loss.
What glands are found in the skin layer of the eyelid?
Sebaceous glands:
- Glands of Zeiss – empty into eyelash follicles.
- Meibomian glands – extend from lid margin into tarsal plate; produce oily tear film.
Apocrine sweat glands:
- Glands of Moll – located between lash follicles.
What is contained in the subcutaneous layer of the eyelid?
Loose connective tissue with elastic fibers and blood vessels, allowing mobility between the skin and underlying muscle.
What type of muscle is the orbicularis oculi, and what is its function?
It is a striated (voluntary) muscle responsible for closing the eyelids and aiding in tear drainage.
What is the origin and innervation of the orbicularis oculi?
Origin: Medial palpebral ligament (on the nasal side).
Innervation: Temporal and zygomatic branches of the facial nerve (cranial nerve VII).
Describe the fiber arrangement of the orbicularis oculi.
The fibers run in a zipper-like fashion from the lateral to the medial canthus, helping propel tears into the puncta.
Into how many parts is the orbicularis oculi divided?
Three main parts:
- Orbital portion
- Preseptal portion
- Pretarsal portion
What are the features and functions of the orbital portion of orbicularis oculi?
- Lies over the extraorbital bones and surrounds the orbital margin.
- Closes the eyelids forcefully (as in squinting).
- Responsible for voluntary eyelid closure.
What is the function of the palpebral portion of orbicularis oculi?
- Controls gentle closure of the eyelids, such as winking and reflex blinking.
- Blinking occurs about 10–15 times per minute and is reflexive, not dependent on light perception.
What are the two divisions of the palpebral portion?
Preseptal portion
- Fibers run from medial palpebral ligament (MPL) to lateral palpebral raphe (LPR).
Pretarsal portion
- Fibers pull the eyelid medially during contraction.
- Contains a lacrimal portion that extends behind the lacrimal sac.
- Functions as a tear pump during blinking, creating pressure to move tears through the nasolacrimal duct.
What is the orbital septum? What nerve innervates the orbital septum?
- It’s a membranous sheet extending across the palpebral portion of the upper and lower eyelids.
- The superior division of the oculomotor nerve (cranial nerve III).
What structure perforates the orbital septum? Where does the orbital septum insert?
- The aponeurosis (fan-like tendon) of the levator palpebrae superioris.
- At the distal tarsal plate.
What is the function of the upper portion of the levator muscle?
It raises the upper eyelid voluntarily.
