Lacrimal Gland Flashcards
What kind of gland is the lacrimal gland
Exocrine gland (like the mammary and salivary gland)
Myoepithelial creates
Force for excretion of tears
Lacrimal gland develops from multiple
Ectoderm buds at anterior superolateral orbit
Lacrimal glands may not function fully for up to
6 weeks after birth
Might explain why newborn dont produce tears when crying
When someone has extreme dry eye
Scar tissue will form over the cornea.
Why dont artificial tears work too well
No growth factors
So there is nothing to stimulate the the epithelium to grow so it doesn’t help it heal
During sleep, secretion of all major proteins and water
Is inhibited
Total removal of the main lacrimal gland
Does not in itself lead to dry eye
Removal of parasympathetic innervation to the lacrimal gland
Leads to rapid reduction in tear flow
sensory input for cornea
CNV
In healthy individuals, everyday ocular surface stimulation like mechanical irritation, low humidity, excess wind and CLs triggers
Neural signal that initiates reflex tear secretion (CNV)from the main and accessory lacrimal glands
Tear reflex corneal nerves
CNV in
CNVII out
Inflammation interrupts normal homeostasis and leading to
Ocular surface disease and dry eye involving Cytokines secretion which disrupts neural arc
Basal aqueous secretion decreases with
Age and during sleep
What causes aqueous secretion?
CNV (most common)
- dazzle (IIN)
- taste (VIIN)
- cough/sneeze /laugh (IXN, XN)
True tear allergan
Irritates nasal mucosa to stimulate tear production
Loss of water from the tear film leads to increased osmolarity and tears become more
Concentrated
When evaporation increases (tonicity)
Tonicity increases
When flow rate increases (tonicity)
Decreases
When flow rate decreases
Tonicity increases
When tonicity increases. Water is
Drawn from the cornea and the cells dry - irritating the eye
Low tonicity leads to
Corneal edema
High tonicity leads to
Corneal dehydration
Diurnal rhythm in lacrimal secretion
NONE
Tear production is stimulated by ___ agents. And decreased by _____agents.
Stimulated by cholinergic (policarpine)
Decreases by anto cholinergic (antihistamines)
Newborns secrete tears in the first
24 hrs
Hypotonic tears result from
Increased stimulation (more fluid & less dissolved protein)
Hypertonic tears result from
Decreased stimulation
Evaporation (increase concentration by 10-20%)
Hypersecretion of tears occur from
Irritation (CNV)
Foreign body, trauma, disease of cornea/conjunctiva of eyelid, nasal mucosa
Hyposecretion of tears occur from
SJORGENS SYNDROME
Inflammatory disease of salivary and lacrimal gland
Scarring due to infection
Typical tonicity range of tears
304-318 moms/L
Osmolarity changes in CL wearers
Osmolarity decreases (tearing) initially then increases with adaptation
Osmolarity of dry eye
Higher than 318 mosm/L
Cornea temperature
Lower than the rest of the body (35-36 degrees celcius)
Inflammatory enlargement of lacrimal gland
Dacryoadenitis
Unilateral, infection of some sort
Approximately 50% of all lacrimal gland masses are
Inflammatory, other half are neoplasms
The proper position of the eyelids against the globe and the position of the puncta to the tear lake are important for
Capillary attraction to draw the tears into the canaliculi
If lids fold out , the tears wont touch the ocular surface and
Wont be able to drain (capillary attraction)
Tears are removed by ____ attraction due to the vacuum formed in the lacrimal sac. This is influenced by ___ which creates the pressure.
Capillary
Orbicularis muscle
The amount of tears present on the ocular surface at any given time is a function of both
Secretion of components that make up the tears and the drainage and evaporation of tears
Drainage is via
Punctures -> canaliculi -lacrimal sac-> nasolacrimal duct to the valve of Hansel to nose
Tears move into the puncta due to
Capillary attraction
A sticky, watery eye with positive regurgitation on pressure over the lacrimal sac conforms the diagnosis
Epiphora
Common in children
Usually resolves on its own
Nasolacrimal duct obstruction can cause
Tearing(epiphora) , crusting of eyelids, and lower lid erythema
Nasolacrimal duct obstruction can occur due to
Chronic sinus disease, involutional stenosis, dacryocystitis or nasoorbital trauma
Epiphora IN CILDREN can be caused by
Obstruction of nasolacrimal passage or NON OBSTRUCTIVE factors such as EYELID MALPOSITION, pump insufficiency , tear film instability, or hypersecretin
Epiphora in adults is caused by
Disturbed ocular surface tear flow such as lid malpositon (dry eye, blepharitis, TRICHIASIS)
ECTROPION
In adults most common cause of epiphora is
Nasolacrimal duct obstruction
Most common cause of inflammation of the canaliculus
Gram positive rod
Severe dacrocytis can
Break through the skin
Acute dacryocystitis is
Inflammation of the punctum
May have a fever - tells you there is in infection
Disorders of the tear drainage can be caused by (2)
Irritation of ocular surface or occlusion of any part of the drainage system
Lower cannaliculus drains 60% of the tear layer due to
Gravity
Irrigation of the lower lacrimal system under topical anesthetia shows
How much drains
Dacryocystitis
Obstruction of nasolacrimal duct
