Ocular Physiology 1 Lacrimal Apparatus Flashcards
What type of gland is the lacrimal gland?
Tubuloacinar gland derived from surface ectoderm
What lines the lacirmal ducts?
Low columnar or cuboidal epithelium
What nerve innervate the lacrimal gland?
Postganglionic secretomotor fibres (from the pterygopalatine ganglion) hitch hike on the zygomaticotemporal and lacrimal nerves
Where else do lacrimal secretions come from
Accessory lacrimal tissue in the conjunctiva
What mediates reflex tearing?
Parasympathetic nerves that stimulate myoepithelial cells lining the lacrimal acini, causing them to contract
Where do the parasympathetic fibres that stimulate reflex tearing originate?
Superior salivatory nucleus
How to sympathetic nerves influence tear production?
Altering blood flow to the lacrimal gland
What are the layers fot he tear film?
Lipid layer
Aqueous layer
Inner hydrophilic mucin layer
How thick is the mucous layer of the tear film?
30 micrometers
Where are mucin secreting goblet cells concentrated?
Inferonasally in the conjunctiva
What is the stability of the tear film dependent on ?
Epithelial glycocalyx, antievaporative effects of the lipid layer, viscous properties of the tears imparted by the mucin layer
What is normal tear film break up time?
10-30 seconds
What is the maximal volume of the conjunctival sac?
20 microlitres
What is normal tear volume
6-7 microlitres
What % of an average drop of medication is retained
20%
What is a normal Schirmer’s test?
15-25mm of wetting over a period of 5 minutes
How are tears biochemically formed
Secretion from the acinar region of the lacrimal gland is an ultrafiltrate of plasma
Later modified by ductal secretion of potassium chloride
What is the osmolarity of the aqueous layer? pH?
Osmolarity is that of normal saline
pH 7.4
Why is the glucose concentration in the aqueous layer lower than that of plasma?
Precorneal tear film and limbal vessels supply the corneal epithelium with glucose
