CL - Extended Wear - Week -3 Flashcards
Define Extended Wear (EW) and Continuous Wear (CW)
EW: CLs worn continuously for a period of up to 7 days (6 nights)
CW: CLs worn continuously for up to 30 days
What is adequate oxygen supply to the cornea essential for? (2)
Normal epithelial aerobic metabolism
Elimination of waste products
How can the wearing of low oxygen transmissible contact lenses affect the cornea? (1)
Corneal hypoxia and oedema.
Oxygen-deficient corneal metabolism leads to an accumulation of lactate, which lowers the rate of fluid pumped out of the cornea. This leads to oedema/swelling.
How does sleep (eyelid closure) affect: corneal oxygen levels, lens temperature, tear pH, and tear osmolarity
Corneal oxygen: reduces by 4%
Lens temperature: up by 2 degrees (C)
Tear pH: more acidic
Tear osmolarity: reduces (hypotonic shift)
By how much does the cornea swell during sleep?
4% on average
By how much does oedema reduce during the day in: hydrogel EWs, and RGP EWs?
Hydrogel: 8% reduction in oedema
RGP: 10% reduction in oedema
What is the minimum Dk/t set by Holden-Mertz for daily wear and overnight wear lenses?
Daily: 24
Overnight: 87
What revision to the Holden-Mertz criteria is being considered and why?
EW critical Dk/t set to 125 to prevent stromal anoxia
Is corneal swelling uniform? Explain
No it isn’t
Peripheral > central
Are adapted contact lens wearers more resistant to corneal swelling than non contact lens wearers or vice-versa?
Adapted contact lens wearers are more resistant to corneal swelling
What is the minimum concentration of oxygen for no reduction in physiological function?
~10%
List 6 possible indications for EW contact lenses
Convenience Aphakes (absence of lens in eye) Anisometropic infants Therapeutic Occupation Pre-refractive surgery
List 4 therapeutic uses for EW contact lenses
Bullous keratopathy
Dry eye disease
Post corneal surgery
RCEs
List 8 lifestyle considerations for EW contact lenses
Strong hx of CL non-compliance Smoking Regular Swimming Chronic bleph or MGD Severe drye eye Previous corneal inflammatory events Immunocompromise
Why do we not use hydrogel soft contact lenses?
They do not meet Holden-Mertz criteria
Do RGP lenses meet the Holden-Mertz criteria?
yes
What ocular effect of hydrogel extended wear lenses is evident after a few hours of wear?
Limbal hyperaemia
List 6 ocular effects of hydrogel EW wear
Limbal hyperaemia Epithelial microcysts Stromal oedema Stromal neovascularisation Endothelial blebs Endothelial polymegathism
What are epithelial microcysts, and when do they occur in a hydrogel EW lens patient?
5-30um inclusions composed of necrotic cells/debris that occur after more than 2 months of corneal hypoxia
Where do epithelial microcysts originate?
originate deep in the epithelium and migrate anteriorly over time
How can you examine epithelial microcysts?
reversed illumination with retroillumination
Is stromal oedema from Hydrogel EWs acute or chronic? Is it reversible?
Acute and reversible
How can you resolve stromal neovascularisation in a hydrogel lens wearer? How long does this take?
Vascular response regresses after 1 month of re-fitting to a higher Dk/t lens
What are endothelial blebs? How long do they last after lens removal?
Short term oedematous cells that disappear within ten minutes of lens removal
Describe endothelial polymegathism. Why does it occur and what can it lead to?
a permanent increase in variability in the size of corneal endothelial cells in response to chronic hypoxia. Contact lens intolerance is likely with time
Describe Corneal Exhaustion Syndrome. What symptoms are involved? (6)
a syndrome characterised by lens intolerance, endothelial polymegathism, and ongoing change in corneal refraction and astigmatism
Symptoms include:
redness, photophobia, lacrimation, stinging, blur, discomfort
Who is indicated for rgp extended wear lenses?
daily wearers of RGPs with hyper-DK lenses
List 5 advantages of RGP EW lenses
reduced hypoxic effects reduced inflammatory responses enhanced lens durability enhanced optical clarity reduced sensation of 'dryness'
List 3 ocular side effects of RGP EWs
Lens adherence (immobile upon waking)
3+9 o’clock staining (sign of peripheral corneal dessication)
Superior eyelid ptosis
Describe the incidence of lens adherence in rgp extended wear patients. What does it lead to?
10-22% of patients. Leads to corneal distortion
What are 3 risk factors for lens adherence?
Thinner corneas
Tight eyelids
Low amounts of corneal cyl
What may 3+9 o’clock staining lead to? (2)
Vascularised limbal keratitis
Corneal thinning
What are 3 risk factors for 3+9 o’clock staining? (3)
Higher baseline conj hyperaemia
Viscous tear film
Poor lens centration
How are silicone hydrogels able to have much more oxygen permeability (Dk) than hydrogels?
Hydrogel lens transports oxygen mainly by the water in the lens, therefore, high water content means high oxygen permeability. Even when the water content of the lens is as high as 99%, the oxygen permeability would not go over the theoretical value, which is 40. As for the silicone hydrogel lens, although it also contains water, oxygen is not transported by water; instead, it is delivered by the polymer which consists of silicon molecule chains. The theoretical value of silicon molecule’s oxygen permeability can be more than 100; therefore, silicone hydrogel lens’ oxygen permeability is much higher than hydrogel lens’, which depends on water to transport oxygen.
Is oxygen transmissiblity linked to water content in silicone hydrogels? How does this differ from regular hydrogels? Explain
no. While oxygen transmissibility is permeability divided by lens thickness. The permeability in Si-Hy is determined by the silicone polymer and not by water (unlike hydrogels)
What is the maximum extended wear time for the following Si-Hy EW lens options? (6) Alcon focus Alcon air optix B&L purevision B&L purevision 2 Coopervision biofinity J&J acuvue oasys
Alcon focus night and day: 30 nights Alcon air optix aqua: 6 nights B&L purevision: 30 nights B&L purevision2: 30 nights Coopervision biofinity: 6 nights J&J acuvue oasys: 6 nights
What is the extended wear adaptation schedule for a patient with no contact lens experience?
Daily wear with normal adaptation schedule for minimum of 2 weeks and gradually increase wear time.
Aftercare at 2 weeks before commencing overnight wear.
What is the extended wear adaptation schedule for an experienced CL wearer? (5)
Aftercare after first night of overnight wear
Aftercare after 6 nights of extended wear
Aftercare before lens replacement (for monthly disposable)
Aftercare after 3 months
Minimum routine after-cares every 6 months
What advice can be given to contact lens patients?
If in doubt, take it out
What does RSVP mean for contact lenses?
A patient should remove contact lenses if they notice: Redness, Soreness, Vision change, Photophobia
How do silicones compare to hydrogels for extended wear in terms of: Hypoxia, risk of MK, rate of mechanical prob lems, rate of sterile infiltrates?
Hypoxia: greatly reduced
Risk of MK: unchanged
Rate of mechanical problems: unchanged or slightly greater
Rate of sterile infiltrates: higher (double)
What are mucin balls and where can they be found?
pearly, transluscent, spherical particles found between the back surface of the lens and the cornea
What are mucin balls composed of, how do they form, and when the lens is removed what is seen?
accumulation of post-lens debris: shearing of tear film rolling of debris into balls. Consist of mucin and lipid. When lens removed, transient depressions are seen in the epithelium
List two mechanical effects of Si-Hy EW
- Superior epithelial arcuate lesions (SEALs) [full thickness epithtelial split, with jagged edges)
- Conjunctival Flaps (separation of conj epithelium)
Where do SEALS occur? What about conjunctival flaps? Are they symptomatic?
SEALS: usually ~1mm from superior limbus
Conj. flaps: up to 1mm away from lens ege
Usually both are symptomatic
Following epithelial repair in superior epithelial arcuate leions, what is indicated? How about for conjunctival flaps?
Refit indicated for both
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?
Mimimal 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 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
