116 Questions
Which muscle is responsible for the primary lateral depressor of the eyebrow?
Orbicularis Oculi
At what stage of development do the eyelids form from the folds of surface ectoderm filled with mesenchyme?
2nd month
Which cranial nerve innervates the muscles responsible for eyebrow movements?
CN VII (Facial)
What is the main function of the eyelids?
To cover the globe for protection
What is the most common type of blinking?
Spontaneous blinking
What sensory stimuli can elicit a blink reflex?
Touch
What is the role of Bell's Phenomenon during a blink?
Outward rotation of the globe
What is the role of the eyelids in tear production?
Stimulate the secretion of lipid from the Meibomian glands
What is the function of the muscle of Horner in tear drainage?
It contracts upon eyelid closure to pump tears into the lacrimal sac
What is the function of eyelashes?
To induce blink reflexes
What is the condition characterized by the inability to oppose the eyelids on attempted lid closure?
Lagophthalmos
What is the common cause of yellow plaques of lipid near the inner canthus?
Hyperlipidemia
What is the condition characterized by the loss of eyelashes?
Madarosis
What is the condition characterized by the eversion of the eyelid margin?
Ectropion
What is the vertical fold of skin at the nasal canthus that gradually disappears as the bridge of the nose develops?
Epicanthus
What is the condition characterized by the upper eyelid drooping or sagging?
Ptosis
What is the function of the lacrimal punctum?
To drain tears from the eye into the lacrimal sac
Where is the superior palpebral crease located?
In the upper eyelid
What separates the tarsal and orbital portion of the upper eyelid?
Superior palpebral sulcus
What is the function of the malar crease?
To mark the junction of the eyelid with the cheek
Where is the caruncle located?
Medial to the plica semilunaris
What is the function of the plica semilunaris?
To allow lateral movement of the eye
Where are the lacrimal puncta located?
At the medial canthus
What is the function of the lacrimal lake?
To provide a reservoir for the pooling of tears
Where are the meibomian glands located?
Posterior to the cilia inside the tarsal plates
What is the function of the tarsal plate?
To support the lid margin and maintain its shape
What divides the eyelid margin into lacrimal and ciliary portions?
Lacrimal papilla
Which layer of the eyelids contains the palpebral portion of the orbicularis oculi?
Orbicularis layer
What is the function of the orbital septum in the eyelids?
Serves as a barrier and restricts fat from falling onto the lid margins
Which muscle is a specialized area within the palpebral portion of the eyelids used for spontaneous and reflex blinking?
Muscle of Riolan
Which glands are large sebaceous glands located posterior to the eyelashes and produce the lipid layer of the tear film?
Meibomian glands
What provides sensory innervation to the eyelids?
Trigeminal nerve
Which muscles are part of the posterior muscular system of the eyelids?
Superior levator palpebrae muscle and superior and inferior tarsal muscle of Muller
What are the Glands of Zeis associated with?
Protection of eyelash follicles
Where is the palpebral conjunctiva located?
Inner lining of the eyelids
What are the Glands of Moll associated with?
Sweat gland for the eyelash follicles
Which nerve provides voluntary motor innervation to the eyelids?
Temporal and zygomatic branches of the facial nerve
What is the composition of the tarsal plate in the eyelids?
Dense irregular connective tissue and contains palpebral ligaments
What is the function of the Meibomian glands in the eyelids?
Produce the lipid layer of the tear film
What provides involuntary motor innervation to the eyelids?
Sympathetic nervous system
Which structure ensures the smooth movement of the eyelids over the globe?
Tarsal conjunctiva
What is the main function of the caruncle?
To provide a source for the collection of matter
Which condition is characterized by an opaque, slightly elevated mass of modified conjunctival tissue in the interpalpebral area?
Pinguecula
What is the composition of follicles in the conjunctiva?
Lymphoid hyperplasia, allergic response
Where are papillae generally located?
Lower lid
What is the function of the plica semilunaris?
To reduce stretching of the conjunctiva on lateral movements
What is the main cause of yellow plaques of lipid near the inner canthus?
Allergies
What is the condition characterized by fibrovascular overgrowth of bulbar conjunctiva into the cornea?
Pterygium
What supplies blood to the palpebral and fornix portions of the conjunctiva?
Peripheral arcade
Which structure contains smooth muscle, goblet cells, and adipose tissue?
Plica semilunaris
What is the main cause of follicles and papillae in the conjunctiva?
Lymphoid hyperplasia
What is the main function of the bulbar conjunctiva?
To allow underlying sclera to shine through
What is the main function of the lipid layer in the tear film?
Retard evaporation and provide lubrication for smooth eyelid movement
Which layer of the tear film contains antibacterial substances such as lysozyme and lactoferrin?
Aqueous layer
What is the primary source of atmospheric oxygen for the cornea?
Aqueous layer
Which component of the tear film contains peptide growth factors and cytokines that can regulate ocular surface wound and repair?
Aqueous layer
What is the normal Tear Break Up Time (TBUT)?
15-45 seconds
What is the main cause of Congenital Dacryostenosis?
Incomplete canalization of duct
What is the most common congenital lacrimal abnormality?
Congenital Nasolacrimal Duct Obstruction
What is the characteristic symptom of Canaliculitis?
Pain, swelling, erythema, and discharge
What is Dacryocystitis usually caused by?
Obstruction of the nasolacrimal duct
What is the recommended treatment for Acute Canaliculitis with a pouting puncta?
A posterior cut down of the canaliculus and curettage of the granules
What is the main cause of Dacryoadenitis?
Inflammatory enlargement of the lacrimal gland
What is the characteristic symptom of Dacryocystorhinostomy (DCR)?
Tear drainage procedure
What is the total volume of tears on the ocular surface?
7 to 10 μl
What is the normal tear production rate per minute?
1 μl/min
What is the average tear film pH?
7.45
What is the function of the lacrimal gland's orbital portion?
Secretory function
What is the composition of the lacrimal gland's reflex secretion?
Water and electrolytes
Which nerve pathway is involved in reflex tearing?
Trigeminal nerve and sympathetic pathway
What is the role of the lacrimal gland fluid?
Spread across the ocular surface by blinking
What artery supplies the lacrimal gland?
Lacrimal artery
What is the primary innervation of the lacrimal gland?
Trigeminal nerve
What is the role of the mucous layer in the tear film?
Aids in adhesion and microbe entrapment
What is the composition of the normal tear film?
Isotonic
What is the role of the eyelids in tear distribution?
Spreading the mucous layer evenly over the corneal epithelium
Where are the lacrimal puncta located?
At the junction of the lacrimal and ciliary portions of the eyelid margin
What is the function of the valve of Hasner in the nasolacrimal duct?
Prevents retrograde movement of fluid up from the nasal cavity
What is the main function of the common canaliculus (ampulla of Maier) in the nasolacrimal drainage system?
Joins the upper and lower canaliculi to form a single duct
What is the role of the lacrimal sac in tear drainage?
Acts as a reservoir for excess tear fluid
What is the function of the orbital septum in relation to the lacrimal sac?
Surrounds and protects the lacrimal sac
What is the function of the valve of Rosenmuller in the nasolacrimal drainage system?
Prevents reflux at the entry of the common canaliculus into the sac
What is the role of the Horner’s muscle fibers in the nasolacrimal drainage system?
Surround the walls of the canaliculi
What is the main function of the membranous folds within the sac and nasolacrimal duct?
Act as valves to regulate tear flow
What is the function of the lacrimal punctum in the nasolacrimal drainage system?
Serves as the entry point for tears into the canaliculi
What is the role of the lateral displacement of the lateral wall during tear drainage?
Prevents overflow of tears into the conjunctival tissue
What is the primary function of the corneal endothelium?
Regulate water and ion flow from the aqueous humor
Which layer of the cornea contains cells that do not replicate and wear out with age?
Endothelium
What is the normal range of corneal endothelial cell density in adults?
2500-3000 cells/mm2
What is the total refractive power of the eye, and how much of it is attributable to the cornea?
60-65 D total, 20-25 D attributable to the cornea
What is the primary source of atmospheric oxygen for the cornea?
Diffusion from the aqueous humor
Which nerve provides voluntary motor innervation to the eyelids?
Facial nerve
Where are the corneal nerves located?
Epithelium
What is the function of the lacrimal gland's orbital portion?
Produce basal tears for ocular surface lubrication
What is the composition of the normal tear film?
Mucous layer, aqueous layer, lipid layer
What provides sensory innervation to the eyelids?
Ophthalmic nerve
What is the main cause of Dacryocystitis?
Bacterial infection
What is the main function of the membranous folds within the sac and nasolacrimal duct?
Regulate tear drainage
What is the approximate thickness of the corneal epithelium?
30 μm
Which layer of the cornea is composed of collagen fibrils and is prenatally produced?
Bowman’s layer
What is the primary function of the corneal Bowman’s layer?
Provide structural support
What is the approximate thickness of the corneal stroma?
500 μm
What contributes to the transparency of the corneal stroma?
Arrangement of collagen fibers
Which part of the cornea thickens throughout life and consists of two laminae?
Descemet’s membrane
Where are the stem cells for corneal basal cell layer renewal located?
In the corneal epithelium
What is the primary composition of the corneal stroma?
Collagen fibers and ground substance
What is the primary function of the corneal endothelium?
Maintain corneal hydration and transparency
Through which layer do the corneal nerves pass?
Bowman’s layer
Where are the corneal stem cells located?
In a band around the corneal periphery
What is the primary role of the corneal Descemet’s membrane?
To serve as the true basement membrane of the endothelium
What is the radius of curvature of the central cornea?
7.8 mm
Which layer of the cornea is produced by the corneal endothelium?
Descemet's membrane
What is the refractive power of the cornea?
45D
What is the central cornea thickness?
0.53 mm
What is the radius of curvature of the central cornea?
7.8 mm
Which layer of the cornea contributes to the formation of Bowman’s layer?
Corneal stroma
Study Notes
Anatomy and Physiology of the Eyelids
- Palpebral portion of the eyelids is used for spontaneous and reflex blinking
- Muscle of Riolan and Muscle of Horner are two specialized areas within the palpebral portion
- The orbital septum is a dense irregular connective tissue layer that serves as a barrier and restricts fat from falling onto the lid margins
- The posterior muscular system includes the superior levator palpebrae muscle and the superior and inferior tarsal muscle of Muller
- The tarsal plate is made of dense irregular connective tissue and contains palpebral ligaments that hold the tarsal plates in position
- The palpebral conjunctiva is the inner lining of the eyelids, consisting of a stratified squamous epithelial layer and a submucosa
- Meibomian glands are large sebaceous glands located posterior to the eyelashes and produce the lipid layer of the tear film
- Glands of Zeis are modified sebaceous glands associated with eyelash follicles
- Glands of Moll are modified sweat glands associated with eyelash follicles
- The trigeminal nerve provides sensory innervation to the eyelids
- Voluntary motor innervation is provided by the temporal and zygomatic branches of the facial nerve
- Involuntary motor innervation is provided by the sympathetic nervous system
Tear Film and Lacrimal Gland Anatomy
- Mucous layer, composed of glycocalyx and mucin, makes up 30-40% of the total tear film and aids in adhesion and microbe entrapment.
- Eyelids spread the mucous layer evenly over the corneal epithelium, accepting the mucous and creating a hydrophilic surface to accept tears.
- Total volume of tears on the ocular surface is 7 to 10 μl, with normal tear production at about 1 μl/min and the eye's capacity at 20-30 μl.
- Normal tear film is isotonic and its osmolarity varies with factors such as blink rate, humidity, ocular pathology, and contact lens use.
- Average tear film pH is 7.45, with good buffering ability, allowing tolerance of ophthalmic solutions with different pH levels.
- The lacrimal system has a dual function: secretory component contributing to tear formation and excretory component providing drainage from the eye into the nose.
- The lacrimal gland includes the main and accessory glands, meibomian glands, and conjunctival goblet cells.
- The lacrimal gland has orbital and palpebral lobes, with the orbital portion being larger and almond-shaped.
- The gland consists of lobules made of acini, which secrete water, electrolytes, and antibacterial agents, with reflex secretion increasing in response to stimuli.
- The lacrimal gland is supplied by the lacrimal artery and innervated by sensory, vasomotor sympathetic, and secretomotor parasympathetic nerves.
- Reflex tearing occurs in response to external stimuli, with the afferent pathway through the trigeminal nerve and the parasympathetic pathway through the facial nerve.
- Lacrimal gland fluid is secreted into the lateral part of the upper fornix, descends across the anterior surface of the globe, and is spread across the ocular surface by blinking.
Corneal Histological Features
- The cornea is approximately 71mm in size and serves as the principal refracting component of the eye.
- It is transparent and avascular, providing optimal light transmittance, with the anterior surface covered by a tear film.
- The corneal layers, from anterior to posterior, consist of the epithelium, Bowman’s layer, stroma, Descemet’s membrane, and endothelium.
- The corneal epithelium is stratified squamous nonkeratinized epithelium, measuring approximately 50 μm and thickening at the periphery.
- It has three different layers: surface layer, wing cells, and basal layer, each with specific characteristics and functions.
- Cell proliferation occurs in the basal layer, with stem cells located in a band around the corneal periphery, serving as the source for renewal of the corneal basal cell layer.
- The corneal Bowman’s layer is an acellular dense layer composed of random collagen fibrils, approximately 8-14 μm thick, and is prenatally produced, so it cannot regenerate.
- The corneal stroma, also known as Substantia Propria, is approximately 500 μm thick and composed of collagen fibers, keratocytes, and extracellular ground substance.
- Collagen fibers in the stroma are 25-35 μm in diameter, form 200-300 parallel layers called lamellae, and contribute to stromal transparency.
- Corneal Descemet’s membrane is the true basement membrane of the endothelium, thickening throughout life, and consists of two laminae.
- The very regular arrangement of the stromal component and the small diameter of the fibrils contribute to stromal transparency.
- The corneal nerves pass through Bowman’s layer, losing their Schwann cell covering.
Test your knowledge of the anatomy and physiology of the eyelids with this quiz. Explore topics such as the structure of the eyelids, specialized muscles, connective tissues, glandular structures, and innervation. Perfect for students, medical professionals, or anyone interested in understanding the intricacies of the eyelids.
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