CLM - Specialty Contact Lens Fitting - Week 10 Flashcards
What percentage of keratoconic patients fail to adapt to RGP lenses?
10%
List three disadvantages of RGPs for keratoconus.
Initial adaptation and comfort
Lens ejection/stability
Unilateral fitting
List three types of specialty contact lenses.
Corneoscleral lenses
Hybrid lenses
Miniscleral lenses
What is the physically larger diameter RGP lenses of corneo-scleral designs to optimise? What is the comofrt like compared with corneal RGPs?
Optimises centration
Better comfort profile
How do corneo-scleral RGPs interact with the limbus?
They vault the limbus
How does tear exchange occur with corneo-scleral lens designs?
Pumping action
What are E series ACL limbal lift designs for (4)?
Normal eyes
Non-proud grafts
PMD
High ametropia
What are K series ACL limbal lift designs for?
Keratoconus
What are G series ACL limbal lift designs for?
Advanced/highly proud corneal grafts
Compare the cost of E series lenses to regular RGPs.
Marginally more expensive
Are E series lenses more prone to lens ejection? What about debris entrapment?
Very good resistance to both
Can E series lenses be fit unilaterally?
Yes
Can E series lenses be combined with SCLs or are they incompatible?
Can be combined
How do hybrid lenses deal with the main corneal irregularities of corneal ectasia?
Vault them
Are the fitting concepts of hybrid lenses the same as SCLs and RGPs?
No
What are hybrid lense ideal for?
Oval/central/dectentred cones
What three indications may hybrid lenses be suitable for?
Globus/pellucid degeneration
Other corneal irregularities (LASIK induced ectasia or trauma)
Post-INTACs, post-CXL
Are hybrid lenses also suitable for corneal grafts?
No
What are hybrid lenses a priority choice for (5)?
Monocular corrections
Strong history of RGP intolerance
Part-time wear
Dusty/windy occupational environment
Application for sport/recreational activity
What is the aim when vaulting the cornea using hybrid lenses?
Aim for the least amount of vault that allows complete apical clearance
Describe how hybrid lenses are applied to the eye.
Bowl is completely filled with non-preserved saline (and a drop of NaFl when assessing patient’s fitting thechnique)
Patient leans forward with their head parallel to the floor and eye wide open
Lens is gently applied directly to the eye
How do you assess hybrid lens application technique? What do air bubbles indicate?
Check for air bubbles beneath the lens
Cannot be removed by lens manipulation
Requires removal and re-application
During hybrid lens removal, is the use of lubricating drops recommended?
No
What can be worn to optimise grip on the lens when removing hybrid lenses?
Latex gloves
What is the outer landing zone with hybrid lenses? What about inner landing zone?
Outer - Region of the soft contact lens in contact with the cornea
Inner - outer region of the RGP in contact with the cornea
How do the outer and inner landing zones appear with fluorescein?
Outer - a relatively thick dark band
Inner - relatively thinner dark band
Is a feather touch ideal with hybrid lenses or do you want complete clearance? What should be barely visible?
Complete clearance, though with as little vault as necessary
Pupil should barely be visible
What is the most common source of failure when fitting hybrid lenses?
Over-vault
What is next after determining vault depth? What should you start with?
Determining skirt curvature
-start with medium skirt
What should you aim for when determining skirt curvature in terms of fluorescein staining (hybrid lenses, 2)?
Fluorescein thinning in the ILZ
Gentle bearing in the OLZ
What is lens movement like in hybrid lenses?
Similar to soft contact lenses
How do skirts that are too flat or steep stain (hybrid lenses)?
Too flat - OLZ too dark
Too steep - OLZ too bright
-in both cases the ILZ is barely noticed, not ideal, it should be a thin faint line
When the ideal fluorescein pattern is achieved, what should you do (hybrid lenses)?
Over-refraction
How is the vault depth determined with topography-based fitting?
Measure the mean saggital height (um) then use a guide and select a depth corresponding to your mean value and trial it
Adjust accordingly based on fluorescein staining
How is the skirt curvature determined with topography-based fitting? What power map is used?
Measure vertical displacement (mm) of the corneal apex from the centre of the reflected mires using tangential power laps
Select based on a guide, then adjust accordingly
Do minisclerals have movement?
No, essentially none
Are minisclerals a sealed system or does it permit tear exchange?
Sealed system
Are minisclerals considered small or large diameter?
Large
Do minisclerals have a small or large optic zone? What does this mean for edge awareness?
Large optic zone
-minimal edge awareness
Is vision with minisclerals good at night?
Excellent
What are three applications of minisclerals?
All forms of corneal irregularities
RGP intolerance
Dry eye disease or exposure keratopathy
What is the process of miniscleral application?
The same as hybrid lenses
Can gas bubbles be displaced in minisclerals?
No
Describe the process of removing minisclerals.
Manipulate the lower lid against the edge of the lens to encourage tear exchange, breaking the seal
Gently attach the DMV applicator to the edge of the lens and tilt the lens off the eye
Do not suction the applicator to the middle and try pulling it off
What should you quantify when assessing miniscleral fit?
Tear thickness profile across the lens
What two things should you watch out for with minisclerals?
Corneal staining
Conjunctival blanching
