Cellular structure & innervation of the eye Flashcards
What is conjuctiva made out of?
- epithelium
- stroma
- accessory lacrimal glands
what do lacrimal glands do?
secret aq. components of tears
how would you describe the conjunctiva epithelium?
- non-keratinised epithelium (2 to 5 layers) - squamous and stratified
- microvilli
- globet cells
- basement membrane
what do microvilli do?
secret glycoproteins that stabilises the tear film
what are globet cells?
mucin layer of tear film
which glycoprotein stabilises the tear film?
glycocalyx
where does glycocalyx come from?
glycoprotein that is secreted from the microvilli
what is the conjunctiva stroma made out of?
- superficial lymphoid layer
- deep fibrous layer (collagen & elastic layer)
what are the functions of the tear film?
- protection
- lubrication
- vision
- reduce infection risk by washing away foreign particles
what is the tear film composed of? and how are they produced?
- mucin layer produced by globet cells that secret mucin
- aq. layer produced by lacrimal glands and accessory lacrimal glands
- phospholipid layer produced by melibomian glands
describe the mucin layer
hydrophilic surface that stabilises the aq. with the hydrophobic epithelium
describe the aqueous layer
water, growth factors, lactoferrin, lysozymes, immunoglobins, cytokines
describe the phospholipid layer
reduces the evaporation of the aqueous layer
increases surface tension of the tear film, therefore increasing the stability.
whats the maximum volume of conjuctiva sac/tear volume?
7-30 microlitres
whats the maximum volume of an eye drop?
0.025 - 0.07mL
25 - 70 microlitres
how many drops can the conjuctiva support?
roughly one drop
what are the contributing factors of ocular absorption of eye drops?
- Tear volume (7-30 microlitres)
- Tear turnover time (0.5-2.2microlitres/min, may be higher if drug
irritative) - Spontaneous blink rate (~15/min, may be higher if drug is
irritative) - Corneal thickness
- Lipophilic-hydrophilic-lipophilic nature of cornea
how long does drugs remain in the conjunctival sac for?
3 to 5 minutes
how can i increase the drug retention in the conjuctival sac?
apply eye ointment instead of drops - stay longer = better penetration
what is the rate of ocular absorption ?
1 to 7%
what are the functions of the cornea?
mainly to refract to get clear vision
protect against infection and trauma aided by tear film
what are the 5 layers of the cornea? in order
- epithelium
- bowmans layer
- stroma
- descemets membrane
- endothelium
describe the cornea epithelium
- non-keratinised- squamous
- hemidesmosomes
- microvilli
- limbus - tight junctions between cells
what are limbus known as ? and where are they?
epithelium stem cells
in the cornea epithelium
describe the bowmans layer
superficial, strong layer of stromal collagen
avascular, unable to regenerate
scars produced when healing from trauma/injury
describe the stroma
75% water
collagen 1 , 4, 5 and 6
proteoglycan
keratocytes - used to remodel from injuries
describe the descemets membrane
produced and repaired by cornea endothelium
describe the cornea endothelium
monolayer of hexagonal cells
unable to regenerate
describe the cornea
provides nutrition from aqueous, limbus and tear film
transparency
what does the transparency of the cornea depend on?
Correct amount of water in stroma
- Water + nutrients flow passively from aqueous into stroma
- Endothelium prevents overhydration - actively pumps Na+ back into aqueous (Na+/K+ ATPase), water follows Na+ passively
Regular orientation and spacing of collagen fibres
what is the episclera?
loose connective tissue overlying the sclera
that provides the nutrition to sclera
also providing low friction to allow free movement of the eye
what is the episclera composed of?
- inner layer
- intermediate loose connective tissue
- outer layer - muscle sheaths fused & conjuctiva at limbus
and heavily vascularised
- anterior and posterior plexus
describe the stroma
Tough outer coat of eye
Continuous with cornea and optic nerve
Avascular but pierced by vessels
Collagen (mainly types I, III, V, also IV, VI, VIII) Proteoglycans, glycoproteins, elastin
Layers:
1. Outer stroma – criss-cross arrangement collagen bundles
2. Inner lamina fusca – blends with uveal tract, separated from it by potential space (suprachoroidal space)
what are the main functions of the sclera?
- protect
- maintain shape
- tolerance of intraocular pressure fluctuations
- blocking of light
what are the three components of the uveal tract?
- iris
- choroid
- ciliary body
what is the iris composed of?
- Anterior surface - Connective tissue, incomplete border layer overlying
stroma - Stroma
- Contains vessels, nerves Sphincter pupillae(circular)
- Smooth muscle (short ciliary nerves – CNIII – parasympathetic)
- Dilator pupillae (radial)
- Smooth muscle (sympathetic supply, carried by long ciliary
nerves (Va))
- Posterior epithelium
- Cuboidal, pigmented
what is the function of the iris?
control the pupil size to regulate light, depth of focus, minimising optical aberrations
blood-aqueous barrier due to the tight junctions between the iris and endothelium cells
what is the ciliary body composed of?
Ciliary epithelium
- Cuboidal bilayer, apex to apex, gap junctions
- Inner layer – nonpigmented, high metabolic activity
- Outer layer – pigmented
- Ciliary muscle
whats the function of the ciliary body?
- Blood aqueous barrier (tight junctions between inner nonpigmented cells)
- Aqueous humour production (both epithelial layers)
- Accommodation (ciliary muscle)
- Contracts => zonules relax => lens fattens =>
enables focus on near objects
- Parasympathetic (short ciliary nerves CNIII)
whats the structure of the choroid? in order
bruchs membrane
choriocapillaries
stroma - larger blood vessels
whats the function fo the choroid?
Vascular supply:
1. Nutrition
2. Waste removal
3. Heat dissipation
4. Ocular immunity
describe the vitreous
80% ocular volume
99% water
Transparent “gel”
Hyaluronic acid
Collagen (II, IX, V/XI hybrid)
describe the lens
- 30% refractive power of eye
- Capsule - Basement membrane
- Epithelium
- Cuboidal and non-mitotic centrally
- Columnar and mitotic peripherally - Fibres
- Cells elongate and lose organelles, become fibres.
- Confer transparency
- Nucleus – older fibres, cortex – newly formed fibres - Zonules
- Sheets of suspensory fibres
- Made of fibrillin
- Attach ciliary body to lens at and around its equator
what are the contents of the lens?
- low water (65%)
- high protein (35%)
- relatively hypoxic
- clarity
- Narrow lens fibre membranes
- Small interfibre spaces
- Tightly packed regular contents (crystallin)
- Absence of blood cells
- Loss of organelles from cells when they => fibres
what is the structure of the retina?
RPE (pigment epithelium)
- Hexagonal monolayer epithelial cells
- Microvilli – envelop photoreceptor outer segments
- Tight junctions – outer blood-retinal barrier
- Rich in mitochondria
- Basement membrane – forms part of Bruchs membrane
LOOK AT NOTES FOR MORE ON RETINA AND RPE
describe the photoreceptors
- Rods - Low light vision, peripheral vision
- Cones - Bright/normal, central vision, colour vision
- Light perception by outer segments of photoreceptors
- G proteins – “opsins”
- Vitamin A derived molecules (chromophores)
describe the ganglion cells
Optic nerve - produced a Light signal => brain
1. Parvocellular - Fine vision, colour, Mainly in fovea
2. Magnocellular - Motion, coarse vision, Peripheral
what nerves are important to the eye?
