Cornea

Question 1

Conjunctiva function

Answer 1

Joins sclera to eyelid
Tear production/stability
Immune functions for ocular surface

Question 2

Regions of conjunctiva

Answer 2

Palpebral: innermost eyelid. Visible meibomian glands (white spots)
Fornix: vascularized, lacrimal ducts, caruncle and plica semilunaris
Bulbar : binds to sclera

Question 3

Epithelium of conjunctiva

Answer 3

Columnar with goblet cells in crypts of Henle

Limbal (near iris) has less goblet cells, more vascular for stem cells

Question 4

Conjunctival sub-mucosa

Answer 4

Below conjunctiva epithelium
Superficial lymphoid layer: immune cells
Internal fibrous layer: nerve cells

Question 5

Conjunctiva vasculature

Answer 5

Anterior ciliary arteries and palpebral branches of nasal and lacrimal arteries
Drained by: sup./inf. Palpebral/ophthalmic veins

Question 6

Conjunctiva innervation

Answer 6

CN V: long ciliary nerves, V1 ophthalmic division

Question 7

Lacrimal apparatus function

Answer 7

Tear secretion / distribution / elimination

Question 8

Tear film composition

Answer 8

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

Question 9

Tear film function

Answer 9

Smooth refraction, antimicrobial, cleaning / lubrication, corneal nourishment

Question 10

Lacrimal gland function/location

Answer 10

Secrets tear film water from lacrimal fossa of orbit roof.

Question 11

Lacrimal gland vasculature and lymphatics

Answer 11

Lacrimal artery branch of ophthalmic artery
Drained by ophthalmic vein
Lymph drained via superficial parotid lymph nodes)

Question 12

Lacrimal gland innervation

Answer 12

Parasympathetic: lacrimal nerve (CN VII)
Sympathetic: superior cervical sympathetic ganglion
Sensory: ophthalmic branch of trigeminal nerve (CNV)

Question 13

Tear film distribution

Answer 13

Blink / gravity directs tear medially. Contractions expands lacrimal sac acting as tear pump.
Tear overflow is epiphora.

Question 14

Tear drainage system

Answer 14

Puncta (upper/lower) lead to canaliculi (upper/lower) leading to lacrimal sac which drains into the nasolacrimal duct to nasal cavity.

Question 15

Schlemm’s canal

Answer 15

Circular drainage channel for aqueous humor
Trabecular meshwork block and eat debris
Drain into aqueous veins

Question 16

Cornea structure from outside to inside

Answer 16

Epithelium 
Bowman's membrane
Stroma
Descemet's membrane
Endothelium

Question 17

Cornea epithelium

Answer 17

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

Question 18

Cornea bowmans membrane

Answer 18

Collagen fibrils, acellular, allows passing corneal nerves to epithelium.
Can scar no mitosis

Question 19

Corneal stroma

Answer 19

90% of mass
Regular spaced collagen fibrils (keratocytes) in bundles (lamellae). Layers bound by bridging fibrils which are surrounded by glycoaminoglycans (GAGs)

Question 20

Descemet’s membrane

Answer 20

Collagen basement. Trauma resistant. Thickens with age.

Terminates in anterior chamber angle forming trabecular meshwork

Question 21

Cornea endothelium

Answer 21

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.

Question 22

Cornea innervation

Answer 22

CN V ophthalmic Division short/long ciliary nerves for stroma / bowman’s layer / epithelial
Unmyelinated post-limbus (transparency)

Question 23

Cornea nutrient supply

Answer 23

Avascular (transparency)
Pos. cornea nourished by aqueous humor
Ant. Cornea nourished by tear film

Question 24

Corneal transparency factors

Answer 24

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

Question 25

Corneal hydration

Answer 25

Water affects thickness, over hydration reduces transparency.
Stroma is hypertonic (sucks water), epi/endothelium block hydration.
Epithelium pump transports CL out and water follows.
Endothelium pump transports HCO3 / Na to aqueous and water follows.

Question 26

Corneal wound repair

Answer 26

Epithelium: no scarring, mitosis
Bowman’s/stromal: scaring
Limbus: serious due to stem cell loss
Endothelium: serious (water entry), no mitosis

Question 27

Sclera and its layers

Answer 27

From limbus (ant. Scleral foramen) to ON (pos. scleral foramen), maintains shape
Contains:
Episclera (outer): separates tenon’s capsule
Stroma (middle)
Lamina fusca (inner): seperates choroid

Question 28

Lamina cribrosa

Answer 28

2/3 scleral fibers turn and exit ON at pos. scleral foramen
1/3 fiber that pierce ON are lamina cribrosa forming pores.
Weak, affected by IOP

Question 29

Episclera layer of sclera

Answer 29

Outermost, vascular connective tissue.

Covered by tenons capsule at pos. and conjunctiva at ant.

Question 30

Stroma layer of sclera

Answer 30

Fibrous with elastin. Provides tensile force, continuous with cornea at limbus.
Reinforce attachments of extra-ocular muscles

Question 31

Lamina fusca layer of sclera

Answer 31

Innermost, loose connective tissue. Brown, separated from choroid by peri choroidal space.
BVs/nerves pass through emissary canals.

Question 32

Sclera innervation

Answer 32

Long ciliary nerve branch of nasociliary at ant. Sclera

Short ciliary nerve branch of nasociliary at pos. sclera

Question 33

Sclera vasculature

Answer 33

Inner sclera avascular, nutrition from outer sclera and choroid
Anterior ciliary arteries supply ant. Sclera.
Long/short posterior ciliary arteries supply posterior sclera (circle of zinn-haller at ON)

Question 34

Scleral color

Answer 34

Yellows with age and fat deposition

Blue with youth or age thinning.