CLM - Extended Wear - PAP Week 1 Flashcards by B H

By what percentage does the cornea swell overnight with eyelid closure?

~4%

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By what percentage does corneal oxygen concentration decrease to with eyelid closure?

Decreases to 4%

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What is the minimum concentration for oxygen for no reduction in physiological function?

~10%

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What happens to lens temperature, tear pH, and tear osmolarity with lid closure (overnight)?

Temperature increases (~2C)
Tear pH decreases
Tear osmolarity decreases

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What is the minimum Dk/t set by the Holden-Mertz Criteria for daily and overnight contact lens wear?

Daily - 24
Overnight - 87

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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

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Is corneal swelling uniform? Explain.

No it isnt
Peripheral > central

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Are adapted contact lens wearers more resistant to swelling than non-contact lens wearers or vice versa?

Adapted contact lens wearers are more resistant

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List 6 possible indications for extended wear contact lenses.

Convenience
Aphakes
Anisometropic infants
Therapeutic
Occupation
Pre-refractive surgery

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List four therapeutic uses for extended wear contact lenses.

Bullous keratopathy
Dry eye disease
Post-corneal surgery
Recurrent erosions

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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

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Are hydrogel soft contact lenses physiologically acceptable for extended wear? Explain?

No, they do not meet the Holden-Mertz Criteria

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What ocular effect is evident after a few hours of wearing hydrogel soft contact lenses?

Limbal hyperaemia

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What is the major factor for limbal hyperaemia? What is tis directly related to?

Hypoxia, directly related to lens oxygen transmissibility

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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

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What size are epithelial microcysts and what are they composed of?

4-30μm
Composed of necrotic cells/debris

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What technique can be used to see epithelial microcysts on a slit-lamp?

Characteristic reversed illumination with retroillumination

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After how long do epithelial microcysts occur (for extended wear in hydrogel) and after what condition specifically?

Typically occurs after >2 months of hypoxia

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Where do epithelial microcysts originate and how do they move?

Originate deep in the epithelium and migrate anteriorly

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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

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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

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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

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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

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Do endothelial blebs persist for long after lens removal?

Disappears within 10 minites of lens removal

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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?

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?

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