wk4: AED - Dry Eye Ax Flashcards
What are the 3 layers of the tear film and how thick are they? [important to know]
Lipid layer - 0.1um
Aqueous layer - 7um
Mucoid layer - 0.05um
Which layer of the tear film do corneal epithelial cells adhere to?
mucoid/mucin layer (adhere to membrane adherent mucins)
Explain how the lipid layer is formed as you blink (4)
Meibomian glands are found in the upper and lower eyelids
Cells on the inner wall of the meibomian gland acini produce oil
When you blink, the lids touch and pressure is applied to the meibomian glands causing them to express small amounts of this oil
The upper lid then pulls the oil upward over the eye as the eye opens
What are the roles of the 3 layers of the tear film?
Lipid layer - helps stabilise tear film and prevent evaporation of the other layers
Aqueous layer - lubricates the eye + wash away particles and prevent infection
Mucin layer - allows tear film to evenly coat cornea and interacts with aqueous layer to prevent tear film from falling off cornea (i.e. helps wettability) (via interaction and adherence to corneal epithelial cells). Also provides underlying cornea with nourishment
How many meibomian glands are present in total on the eyelids (i.e upper + lower eyelids)?
up to 100
What produces each layer of the tear film? (3)
Lipid layer - produced by meibomian glands
Aqueous layer - produced by lacrimal glands (located above the eye and towards the temples)
Mucin layer - produced by the goblet cells within the conjunctiva
Define wettability. Why is this important for our tear film?
Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wetting (wettability) is determined by a force balance between adhesive and cohesive forces.
- Important to prevent/minimise evaporation and dry eye
How can you broadly classify tear-deficient dry eye in terms of conditions? (2)
Sjogren syndrome
- (SSTD, sjogren’s syndrome tear deficiency)
- (further classifies into primary and secondary sjogren’s syndrome)
Non-sjogren sydnrome (NSTD)
How can you classify aqueous-deficient dry eye that is Not sjogren syndrome? (4)
Lacrimal deficiency
Lacrimal gland/duct obstruction
Reflex block
Systemic drugs
How can you classify evaporative dry eye? (2)
Intrinsic causes
Extrinsic causes
How can you classify evaporative dry eye caused by intrinsic causes? (4)
Meibomian oil deficiency
Disorders of lid aperture
Low blink rate
Drug action accutane
How can you classify evaporative dry eye caused by extrinsic causes? (4)
Vitamin A deficiency
Topical drugs preservatives
Contact lens wear
Systemic drugs
What is Sjogren’s syndrome?
chronic autoimmune disease characterised by degeneration of the salivary and lachrymal glands causing dry mouth/glands/eyes
What history questions might you ask if you suspect sjogren’s? (2)
Is your mouth dry?
When you go to bed at night, do you put a glass of water on the bedstand?
What is the Schirmer test?
Is where a paper strip is inserted into the eye (lower eyelid pouch) for several minutes to measure the production of tears. (eyes are closed for 5 minutes during this specifically). The paper is then removed and amount of moisture is measured
What will a schirmer test result look like in patients with sjogren’s
“the paper strip will come out bone dry” - Darryl Guest (because these patients don’t produce tears)
guidelines say anything less than 5ml can be marked as sjogren’s syndrome (if they get more than 5ml then they pass and don’t have sjogren’s syndrome, but that doesn’t mean they don’t still have dry eye)
How do you interpret the results of the Schirmer Test? (from wiki) (4)
Normal: >/= 15ml
Mild: 14-9ml
Moderate: 8-4ml
Severe dry eye: <4ml
*after 5 minutes
And, sjogren’s: expect <5ml (but that doesn’t necessarily mean sjogren’s if they get like 3ml or something, if they get 0ml however it’s quite more likely)
What 2 clinical actions should you do when assessing if something is an autoimmune disease?
History taking (incl family hx)
Blood test
How does corneal sensitivity relate to the tear film?
anything that effects corneal sensitivity will affect the tear film. You need some kind of corneal sensitivity to produce a tear film
Is there an inflammatory component to dry eye?
yes
At what percentage of humidity to humans start getting dry eye symptoms? What is the percentage of humidity in a plane?
Below 40%. Humidity in a plane is 28% so yeah everyone on the plane be getting dry eye
What percentage of the population is estimated to have dry eye? How can you explain this percentage?
About 30%. The reason this is so high might be due to over-diagnosis of dry eye by doctors following trends and fads. There’s probably only about 15-20% that actually have significant dry eye
In the DEWS-II dry eye work up flowchart, list the steps leading to the diagnosis of a normal patient (4)
Presenting patient
Asymptomatic
No signs of ocular surface disease
Normal Patient (no tx required)
In the DEWS-II dry eye work up flowchart: how do you classify a patient with signs of ocular surface disease? (2)
signs without symptoms: predisposition to dry eye
neurotrophic conditions (dysfunctional sensation)
In DEWS-II: how do you manage a patient with signs of ocular surface disease but without symptoms? (1)
Preventative management as appropriate (e.g. post-surgery)
In DEWS-II: how do you manage a patient with signs of ocular surface disease and subsequent neurotrophic condition? (1)
signs indicated management of DED required