Week 10: The Lids Flashcards
What is the embryology of the eyelids?
- Derived from surface ectoderm
- Appear as two circular folds around 2 months
- Folds meet and fuse about half a month later
- At 5 months (post fertilisation) keratinisation of surface epithelial cells initiate the eventual separation of the lids
- Lids are open by 8 months gestation
- Human babies are born with their eyes open
What are the functions of eyelids?
Functions of the Eyelids • Protection (protect from debris) • Contributes to tear production • Spreads tears across the cornea (when blink) • Aids in tear drainage
- The opening between the lids forms the palpebral fissure or aperture
- The fissure is closed
- Medially (nasal) at the inner canthus
- Laterally (temporal) at the outer canthus
What is the inner canthus? (And the caruncle)
• nasal side of the eye
• Forms a small triangular space that contains
> The caruncle – reddish mass of tissue
> A fold of the conjunctiva – the plica semilunaris
• Often obscured in infants by an epicanthal fold of the upper eyelid
• Epicanthal fold remains in some ethnicities
• The palpebral position changes throughout life
What happens to lids as age?
As we age both lids move down
What are the number of rows of eyelashes and total number?
- 2 or 3 rows of lashes
- 100-150 on upper lid
- 50-75 on the lower lid
What glands are associated eyelashes?
- Glands of Moll, modified apocrine (sweat glands) next to the base of the eyelashes
- Glands of Zoe’s sebaceous glands, produce an oil/waxy substance
-glands of Moll and Zies secrete sebum that keeps lashes supple
Where are the lacrimal puncta?
At the nasal end of the lids
- one on the upper lid and one on the lower lid
- involved in tear drainage
- (look like little holes)
Where are the orifices of the tarsal glands visible?
Visible near the lid edge (little holes that are opening to mibomium glands)
What is the structure of the eyelid?
- Skin (front)
• Musculature
• Fibrous layer (including tarsal glands)
• Palpebral conjunctiva (back)
What type of skin cells are the lids made off?
> Skin on the eye lid is the thinnest in the human body > (0.05mm) - Epidermis • Basal layer • Columnar cells • Keratinocytes develop here • Keratin is produced as cells mature • Outermost layers are dead cells and cell remains rich in keratin a hard hydrophobic protein
What is the dermis?
- Layer below the epidermis
- Thin compared to other locations in the body
- Composed of dense irregular collagenous tissue
- Blends into the underlying areolar tissue
- There is no underlying lipid layer here – unlike most other locations in the body (layer of fat)
What are the 3 muscles surrounding the lids? (Musculature)
- Orbicularis oculi
- Levator palpebrae superioris
- Tarsal muscle
What is the orbicularis oculi? What nerve innervation?
- Striated voluntary muscle
- Concentrically orientated
- Has a sphincter like action
- Holds the lid against the eye and assists in spreading tears
- Contraction causes the eyelids to close
-Innervated by the 7th cranial nerve
• Orbital part
• Used in forced lid closure
- Palpebral part
- Used in reflex or spontaneous blinking
What is the Levator palpebrae superioris?
- Striated voluntary muscle
- Only found in the upper lid
- Becomes a tendon as it enters the lid
- Involved in raising the upper lid
- Innervated by the 3rd cranial nerve
- Ptosis caused by paralysis of this muscle
What is the tarsal muscle?
Tarsal Muscle
• Smooth muscle
• Sympathetic innervation
• Lines the levator muscle and helps aids its action
• Also associated with the wide-eyed expression of fear
What is the fiberous layer of the eyelid?
- Gives the lids their shape and firmness
- About 1mm thick
- Contains the tarsal glands (Meibomian glands)
- Modified sebaceous glands
- Produce meibum– an oily secretion at the lid margins
- About 25 glands in the upper lid
- About 20 glands in the lower lid
What is the palpebral conjunctiva?
- Lines the inner surface of the lids
- A mucous membrane
- Non-keratinised epithelium
- Extends into the upper and lower fornix
- Forms the conjunctival sac
What are the dimensions of the conjunctival sac?
- Consists of nonkeratinised epithelium
- Goblet cells, Produce mucin – a wetting agent
- Sac-like structure stops small foreign bodies from passing into the orbit around the globe
- Vascular tarsal conjunctiva also provides oxygen to the cornea when the eye is closed
Where do the lids get their blood supply from?
- Lids are supplied by the vessels from both the orbit and facial arterial systems
- Facial system reaches the lids from-
- Facial artery
- Superficial temporal
- Infra-orbital
Arteries to the eyelid • Orbital system supplies via the following arteries; • Dorsal nasal • Supra-orbital • Frontal • Lacrimal
Arteries to the eyelid • Vessels supply- • Upper lid • Marginal palpebral arcade • Peripheral palpebral arcade • Lower lid • Only a marginal palpebral arcade
What are the somatic MOTOR nerves that supply the lids?
Somatic Motor Nerves • Via temporal branch of the 7th cranial nerve • Stimulation causes contraction of- • Facial muscles around the eye • Orbicularis oculi • Causes lid closure
- Via the 3rd cranial nerve
- Supplies the levator palpebrae superioris
- Stimulation causes upper lid retraction
- More marked on supraduction (up gaze)
What are the somatic SENSORY nerves that supply the lid?
- Lids have a rich sensory nerve supply
- Concentrated at lid margins and lashes
- Stimulation cases lid closure
- Blepharospasm via reflex pathway facial nerve to contract orbicularis oculi
• 5th cranial nerve receives innervation from the eyelids
What is the automatic nerves that supply the lids?
- Smooth tarsal muscle is supplied by sympathetic nerve fibers
- Increased sympathetic activity retracts eyelids and causes wide-eyed effect associated with terror or fright
