Exam prep Flashcards
Problems with loose fitting lenses? (5)
- lens decentration
- lens awareness
- fluctuating vision
- dislodged lenses
- lens popping off eye
Problems with tight fitting lenses? (6)
- lens binding
- poor tear exchange
- limbal redness
- lens indentation
- corneal dessication/staining around lens
- lens getting stuck inferiorly
Problems with spherical RGP on highly astigmatic corneas? (5)
- compromised fitting relationship in one or both meridians
- corneal warpage
- spectacle blur
- inconsistent fitting dynamics
- corneal staining in tight areas
Bennet’s design tricurve and quadcurve
Tricurve:
SCR: add 1.0-1.5mm to BC/0.3mm wide
PCR: add 1.5-2.0 to BC/0.4mm wide
Quadcurve:
SCR: add 0.8mm to BC/0.3mm wide
ICR: add 1.0mm to BC/0.2mm wide
PCR: add 1.4 to BC/0.2mm wide
A change in radius of ___mm results in ___D of change
- 1mm
0. 50D
Symptoms of ghosting, flare or diplopia can be due to what?
pupil not being fully covered by optic zone
What are characteristics of a lens that is too small (3)
- move freely on eye/decentre easily
- dislodge/pop off eye with quick lateral gazes
- looser fitting due to shorter sag height
What are characteristics of a lens that is too big? (4)
- excessive lens tightness
- restrict movement
- limit tear exchange
- may irritate limbal area –> tearing and lens awareness
Large lenses can be particularly problematic when associated with?
high Rx due to thick centre or edges
What are the typical TD/OZ combinations?
<9.00mm (7.0)
9.0-9.3mm (7.5)
9.5-9.8mm (8.0)
>9.8mm (8.5)
To counteract the BC becoming steeper when increasing TD, what should happen to the BC for every 0.5mm increase in TD?
BC should be made 0.05mm flatter (0.25D)
increasing/decreasing TD makes the lens steeper/flatter causing changes in power. What rule is used to help counteract this?
SAM FAP
steeper add minus, flatter add plus
increasing/decreasing TD also has an effect on what other fitting characteristic?
edge lift
increasing TD = increase edge lift
decreasing TD = decrease edge lift
Summarise the effects of a large lens (5)
- fit more tightly
- move less
- can have higher edge lift
- can have more lid attachment
generally more stable
Summarise the effects of a small lens
- fit more loosely
- move more
- can have lower edge lift
- can have less lid attachment
generally less restrictive to tear flow and oxygenation
What parameter has the most influential change on edge lift?
changing SCR
ideal edge lift width?
0.3-0.5mm
How can you modify a high plus power RGP to counter inferior decentration?
add minus carrier on edge
how can you modify a high minus power RGP to counter lid interaction problems?
add plus lenticular –> wedge shape
Why is PMMA a good material to use as a trial lens? (3)
- scratch resistant and machineable
- has no surface charge
When would you consider a lower Dk RGP material? (2)
- to reduce surface deposits
- to reduce flexure
Dimple veiling etiology, signs and management
etiology: gas bubbles trapped in a large post-lens tear film caused by lens being too steep centrally and/or too much edge lift peripherally. Bubbles act like solids and cause pits in the epithelium.
- pool with NaFl
- if significant can cause irregular corneal topography
- decrease vision when located centrally
Mx:
reduce post-lens tear film clearance by reducing sagittal height (if central) or reduce edge lift if source of bubbles from high peripheral tear reservoir
Corneal warpage etiology, signs, symptoms, management
etiology:
- mostly mechanical
- associated underlying cause is prolonged oedema
- ill-fitting lens
signs:
- corneal topographic shape change
- distorted keratometry mires
- irregular retinoscopy results
- indecisive subjective refraction
- reduced BCVA in spectacles
- spectacle blur
symptoms:
- usually asymptomatic as surface irregularity usually masked by CL
- long hours of CL wear
Mx:
Corneal rehabilitation
- change to lenses with increased Dk/t and cease CL wear
- repeat refraction and topography 1-2 weekly until changes stabilise
- withdrawal of original lenses and final refitting
Peripheral corneal staining (3 and 9 o’clock) etiology, signs, symptoms, Mx
etiology:
- lens edge miniscus causing local tear film thinning leading to exposure of the cornea
signs:
- SPK at 3 and 9 o’clock areas (or close)
- SPK shape and appearance can vary widely
- can have assoc adjacent limbal/conjunctival injection
symptoms:
- discomfort/lens awareness
- dryness, gritty, burning
- can be asymptomatic if mild
Mx
- px education
- ATs
- improve blinking
- maximise lens wettability
- minimize surface deposits
- redesign lens to improve fitting
Dellen signs, symptoms, etiology, mx
etiology
- paralimbal elevation which induces a break in the pre-corneal oily tear layer and thus chronic dehydration and thinning
- contributing factors incl; elevations such as pinguecula, pterygium, thick edge RGP, chronic tear film evaporation, chronic 3 and 9 o’clock staining
signs
- characterised by localised thinning of the cornea in a saucer-like depression that pools with NaFl
- often doesnt stain unless epith compromised
- eye usually not inflamed
symptoms
- may complain of vague irritation or photophobia
- no pain
Mx
- temporarily cease RGP wear to allow corneal re-epithelialisation and corneal thickness to return
- lubrication
- determine and manage cause e.g. minimizing 3 and 9 o’clock staining
- if unmanaged - vascularisation, scarring, stromal inflam and degen
Vascularised limbal keratitis signs, symptoms, etiology, Mx
etiology
- mechanical insult to limbal region by edge of RGP lens
- large diameter lenses with low edge lift
- chronic irritation with continuous day and overnight wear may be factor
signs
- opaque elevated mass at the nasal/temporal cornea adjacent the limbus
- limbal vessel engorgement and conj hyperaemia with staining
symptoms
- discomfort
- lens awareness
- decreased wearing time
- redness
- lacrimation
- photophobia
Mx
- cease CL wear temporarily
- change to conservative wearing time
- redesign lens for moderate edge lift
- possibly reduce lens diameter
RGP induced ptosis signs, etiology, Mx
etiology
- mechanical interaction of lid riding over lens edge
- oedema of lid tissue
- inflammation
- lid hypertrophy
- nerve dysfunction
- dehiscence of the aponeurosis of levator tarsal
signs
- characterised by lowering of upper lid, reducing PA over time in RGP wearer
- assoc thickened and red lids
Mx
- temporary discontinuation of lens wear (4-12 wks)
- refit with SCLs
- review lens edge profile
- refer for lid surgery
- rule out other causes
