Cornea Flashcards
Conjunctiva function
Joins sclera to eyelid
Tear production/stability
Immune functions for ocular surface
Regions of conjunctiva
Palpebral: innermost eyelid. Visible meibomian glands (white spots)
Fornix: vascularized, lacrimal ducts, caruncle and plica semilunaris
Bulbar : binds to sclera
Epithelium of conjunctiva
Columnar with goblet cells in crypts of Henle
Limbal (near iris) has less goblet cells, more vascular for stem cells
Conjunctival sub-mucosa
Below conjunctiva epithelium
Superficial lymphoid layer: immune cells
Internal fibrous layer: nerve cells
Conjunctiva vasculature
Anterior ciliary arteries and palpebral branches of nasal and lacrimal arteries
Drained by: sup./inf. Palpebral/ophthalmic veins
Conjunctiva innervation
CN V: long ciliary nerves, V1 ophthalmic division
Lacrimal apparatus function
Tear secretion / distribution / elimination
Tear film composition
Lipid layer (outermost): meibomian / zeis gland secretion, reduces evaporation Aqueous layer (middle): basal (constant) and reflex (crying) via lacrimal gland Mucin layer (innermost): conjunctiva, goblet, plica semilunaris secretion, attaches tear to cornea
Tear film function
Smooth refraction, antimicrobial, cleaning / lubrication, corneal nourishment
Lacrimal gland function/location
Secrets tear film water from lacrimal fossa of orbit roof.
Lacrimal gland vasculature and lymphatics
Lacrimal artery branch of ophthalmic artery
Drained by ophthalmic vein
Lymph drained via superficial parotid lymph nodes)
Lacrimal gland innervation
Parasympathetic: lacrimal nerve (CN VII)
Sympathetic: superior cervical sympathetic ganglion
Sensory: ophthalmic branch of trigeminal nerve (CNV)
Tear film distribution
Blink / gravity directs tear medially. Contractions expands lacrimal sac acting as tear pump.
Tear overflow is epiphora.
Tear drainage system
Puncta (upper/lower) lead to canaliculi (upper/lower) leading to lacrimal sac which drains into the nasolacrimal duct to nasal cavity.
Schlemm’s canal
Circular drainage channel for aqueous humor
Trabecular meshwork block and eat debris
Drain into aqueous veins
Cornea structure from outside to inside
Epithelium Bowman's membrane Stroma Descemet's membrane Endothelium
Cornea epithelium
Stratified tight junctions, secretes glycocalyx (tear film support). Superficial layer (squamous): microvilli for tear attachment Middle layer (wing cells): superficial cell replacement Basal layer (columnar cells): fill gaps, stem cells at limbus (periphery) for cell replacement
Cornea bowmans membrane
Collagen fibrils, acellular, allows passing corneal nerves to epithelium.
Can scar no mitosis
Corneal stroma
90% of mass
Regular spaced collagen fibrils (keratocytes) in bundles (lamellae). Layers bound by bridging fibrils which are surrounded by glycoaminoglycans (GAGs)
Descemet’s membrane
Collagen basement. Trauma resistant. Thickens with age.
Terminates in anterior chamber angle forming trabecular meshwork
Cornea endothelium
Single layer, basal surface on Descemet’s membrane, apical surface on anterior chamber / aqueous.
Gap / tight junctions allows nutrient/water passage from aqueous to stroma.
No mitosis, cell loss from age.
Cornea innervation
CN V ophthalmic Division short/long ciliary nerves for stroma / bowman’s layer / epithelial
Unmyelinated post-limbus (transparency)
Cornea nutrient supply
Avascular (transparency)
Pos. cornea nourished by aqueous humor
Ant. Cornea nourished by tear film
Corneal transparency factors
Avascular, regular collagen fibril length/separation, sparse cell number, tear film.
“lattice theory” fibril interference is cancelled by others, however they may be too small to do this so who knows
