CLM - Extended Wear - PAP Week 1 Flashcards
By what percentage does the cornea swell overnight with eyelid closure?
~4%
By what percentage does corneal oxygen concentration decrease to with eyelid closure?
Decreases to 4%
What is the minimum concentration for oxygen for no reduction in physiological function?
~10%
What happens to lens temperature, tear pH, and tear osmolarity with lid closure (overnight)?
Temperature increases (~2C)
Tear pH decreases
Tear osmolarity decreases
What is the minimum Dk/t set by the Holden-Mertz Criteria for daily and overnight contact lens wear?
Daily - 24
Overnight - 87
What revision to the Holden-Mertz Criteria is being considered, and to prevent what?
Critical Dk/t should be revised to at least 125 to prevent stromal anoxia
Is corneal swelling uniform? Explain.
No it isnt
Peripheral > central
Are adapted contact lens wearers more resistant to swelling than non-contact lens wearers or vice versa?
Adapted contact lens wearers are more resistant
List 6 possible indications for extended wear contact lenses.
Convenience
Aphakes
Anisometropic infants
Therapeutic
Occupation
Pre-refractive surgery
List four therapeutic uses for extended wear contact lenses.
Bullous keratopathy
Dry eye disease
Post-corneal surgery
Recurrent erosions
List 8 lifestyle considerations for extended wear contact lenses.
History of CL non-compliance
Smoking
Regular swimming
Chronic blepharitis or MGD
Severe dry eye disease
History of previous corneal inflammatory events
Delayed wound healing
Immunocomprised
Are hydrogel soft contact lenses physiologically acceptable for extended wear? Explain?
No, they do not meet the Holden-Mertz Criteria
What ocular effect is evident after a few hours of wearing hydrogel soft contact lenses?
Limbal hyperaemia
What is the major factor for limbal hyperaemia? What is tis directly related to?
Hypoxia, directly related to lens oxygen transmissibility
List 6 ocular pathologies that can occur as a result of hydrogel soft contact lenses.
Limbal hyperaemia
Epithelial microcysts
Stromal oedema
Stromal neovascularisation
Endothelial blebs
Endothelial polymegathism
What size are epithelial microcysts and what are they composed of?
4-30μm
Composed of necrotic cells/debris
What technique can be used to see epithelial microcysts on a slit-lamp?
Characteristic reversed illumination with retroillumination
After how long do epithelial microcysts occur (for extended wear in hydrogel) and after what condition specifically?
Typically occurs after >2 months of hypoxia
Where do epithelial microcysts originate and how do they move?
Originate deep in the epithelium and migrate anteriorly
Is stromal oedema with extended wear hydrogel lenses acute or chronic? Is it reversible? What is the occurence of striae and folds (percentage)?
Striae >5%
Folds >10%
Acute and reversible
Define stromal neovascularisation. In what proportion of patients using hydrogel extended wear lenses will this occur?
Formation and extension of new capillaries into the previously avascular corneal stroma
Occurs in ~67% of patients using extended wear hydrogel lenses
Does the vascular response in stromal neovascularisation regress over time after fitting to a higher Dk/t lens or is it completely irreversible?
Does eventually regress after 1 month somewhat
What are endothelial blebs and are they a short or long term response to extended wear hydrogel lenses?
Oedematous cells (blebs) creating dark spots on the endothelial mosaic
Short term response to contact lens wear
Do endothelial blebs persist for long after lens removal?
Disappears within 10 minites of lens removal
What is the aetiology of endothelial blebs?
Altered stromal pH
What is endothelial polymegathism? Is it permanent or reversible? What does it occur in response to?
Increased variability in the size of corneal endothelial cells
It is a permanent change
It occurs in response to chronic hypoxia
Is endothelial polymegathism initially symptomatic or asymptomatic? What is more likely to occur with time with this condition?
Initially asymptomatic
Contact lens intolerance is likely with time
List 6 ocular effects of hydrogel extended wear lenses.
Reduced corneal sensitivity
Reduced epithelial thickness
Corneal distortion
Corneal staining
Stromal thinning
Reversible myopic shift
Define corneal exhaustion syndrome, including what it is characterised by (3) and symptoms (6).
Syndrome characterised by lens intolerancem endothelial polymegathism, and ongoing changes in corneal refraction/astigmatism
Symptoms of intolerance include:
-redness
-photophobia
-lacrimation
-stinging
-blur
-discomfort
Do RGPs cause change to endothelial morphology even after 12 months of extended wear?
No
What is meant by lens adherence in RGPs and when does it occur in extended wear? In what percentage of patients? What does it lead to?
Immobile lens upon waking, occurring in 10-20% of patients
Leads to corneal distortion
What are three risk factors of lens adherence in extended wear RGPs?
Thinner corneas
Tight eyelids
Low amounts of corneal cyl
Aside from lens adherence, list 2 ocular effects of extended wear RGPs.
3 & 9 o’clock staining
Superior eyelid ptosis
What can corneal staining due to extended wear RGPs increase the risk of (2) and what is it a sign of?
Sign of peripheral corneal dessication
Risk of vascularised limbal keratitis or corneal thinning
Consider superior eyelid ptosis due to extended wear RGPs. Is it benign or does it have a sinister cause? Does it resolve after discontinuing RGPs or is it permanent?
Benign but resolves with discontinuation
Is oxygen transmissibility linked to water content?
No
Where does the oxygen permeability of SiHy lenses come from?
Through the silicon component
What is the water and ion transport in SiHy lenses achieved with?
Hydrogel component
What is the extended wear adaptation schedule for a patient with no contact lens experience?
Daily wear with normal adaptation schedule for a minimum of two weeks and gradually increase wear time
Aftercare at two weeks before commencing overnight wear
What is the extended wear adaptation schedule for an experienced contact lens wearer (5)?
Aftercare after first night of overnight wear
Aftercare after six nights of extended wear
Aftercare before lens replacement
Aftercare after three months
Minimum routine aftercare every 6 months
What adivce can be given to patients concerning contact lenses?
If in doubt, take it out
What is meant by the RSVP acronym for contact lenses?
Patients should remove their contact lenses if they feel:
-redness
-soreness
-vision change
-photophobia
Is the risk of microbial keratitis higher, the same, or lower with SiHy lenses compared to extended wear hydrogel lenses? Wha about mechanical problems? What about sterile infiltrates (by how much)?
The same for microbial keratitis
The same for mechanical problems
Rate of sterile infiltrates is approximately double
What are mucin balls and where can they be found?
Pearly, translucent, spherical particles found between the lens and cornea
What are mucin balls composed of, how do they form, and when the lens is removed, what is seen?
Accumulation of the post-lens debris, shearing of the tear film rolling debris into balls
It consists of mucin and lipids
When the lens is removed, transient depressions are seen in the epithelium
List two mechanical effects of SiHy lenses.
Superior epithelial arcuate lesions
Conjunctival flap
Describe superior epithelial arcuate lesions, including appearance and size. Are they typucally asymptomatic? Why do they occur? In what eyes are they more common?
Full thickness epithelial split with jagged edges ~1mm from the limbus
Asymptomatic or mild FB sensation
Usually due to the stiff nature of SiHy
More common in steep corneas
Following epithelial repair in superior epithelial arcuate leions, what is indicated?
Refit
What are conjunctival flaps, where can they be found, are they symptomatic, and do they indicate a refit?
Separation of conjunctival epithelium, occurring up to 1mm away from the lens edge
Usually asymptomatic
Refit recommended
What is giant papillary conjunctivitis?
Immunological response to lens deposit and/or mechanical irritation from the superior eyelid to the lens surface
What is giant papillary conjunctivitis typically associated with?
Contact lens deposits
What cells infiltrate (2) into the eyelid (layer specifically) in giant papillary conjunctivitis?
Mast cells and basophils infiltrate into the superior tarsus
Define corneal infiltrate.
Local or diffuse areas characterised by the infiltration of inflammatory leucocytes into the corneal stroma
Describe the two kinds of corneal infiltrates and primary cause.
Non-infectious/sterile (primary inflammatory reaction)
Infective (primary bacterial infection)
List 8 risk factors for infiltrates with SiHy extended wear lenses.
Corneal neovascularisation
Working outdoors
Microbial contamination of lenses
Tight-fitting lenses
Younger age (<25)
Ametropia >5D
Smoking
Male gender
Describe CLARE, when it typically occurs, and what it is associated with.
Contact lens acute red eye
Sudden morning onset
Associated with colonisation of gram + or - bacteria on the contact lens
List 4 symptoms of CLARE. What kind of disease is it? Can stromal infiltrates be found? Explain (2).
Pain, photophobia, epiphora, irritation
Non-ulcerative, sterile keratitis
Anteiror stromal infiltrates near the limbus
No overlying staining
Does infiltrative keratitis have symptoms?
Nimimal to no patient symptoms
How does infiltrative keratitis appear? List 5 possible causes.
Small focal infiltrates in the peripheral cornea, which pick up staining
Due to chemical toxicity, cellular debris, denatured protein, exo/endotoxins
Define CLPU. What is it a variant of? Describe what it looks like.
Contact lens peripheral ulcer
Variant of infiltrative keratitis specifically associated with contact lens wear
Circular, well circumscribed focal infiltrate <2mm
Is the overlying epithelium lost in a contact lens peripheral ulcer? What is it caused by?
Yesd
Inflammatory reaction due to bacterial adherence or toxins
Are recurrences likely with contact lens peripheral ulcers? What is the recommendation (2)?
Recurrences likely
Recommend ceasing extended wear
Consider daily disposables
What does microbial keratitis involve?
Microbial invasion of the corneal stroma
What is microbial keratitis characterised by (2)?
Corneal excavation and necrosis
What is a common bacteria for microbial keratitis?
Pseudomonas spp.
Describe the PEDALS acronym for differentiating an infectious vs non-infectious inflammatory infiltrate.
Infectious
Pain - yes
Epithelial defect - full thickness
Discharge - possible
Anterior chamber - cells/flare
Location - central/mid-peripheral
Size - >1mm
Non-infectious
Pain - some
Epithelial defect - partial/intact
Discharge - unlikely
Anterior chamber - no cells
Location - peripheral
Size - <1mm
How does fluorescein stain an infectious vs non-infectious infiltrate?
Infectious - pools, fills area of tissue excavation
Non-infectious - patchy, incomplete staining pattern
