Exam prep

Question 1

Problems with loose fitting lenses? (5)

Answer 1

• lens decentration
• lens awareness
• fluctuating vision
• dislodged lenses
• lens popping off eye

Question 2

Problems with tight fitting lenses? (6)

Answer 2

• lens binding
• poor tear exchange
• limbal redness
• lens indentation
• corneal dessication/staining around lens
• lens getting stuck inferiorly

Question 3

Problems with spherical RGP on highly astigmatic corneas? (5)

Answer 3

• compromised fitting relationship in one or both meridians
• corneal warpage
• spectacle blur
• inconsistent fitting dynamics
• corneal staining in tight areas

Question 4

Bennet’s design tricurve and quadcurve

Answer 4

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

Question 5

A change in radius of ___mm results in ___D of change

Answer 5

0. 1mm

0. 50D

Question 6

Symptoms of ghosting, flare or diplopia can be due to what?

Answer 6

pupil not being fully covered by optic zone

Question 7

What are characteristics of a lens that is too small (3)

Answer 7

• move freely on eye/decentre easily
• dislodge/pop off eye with quick lateral gazes
• looser fitting due to shorter sag height

Question 8

What are characteristics of a lens that is too big? (4)

Answer 8

• excessive lens tightness
• restrict movement
• limit tear exchange
• may irritate limbal area –> tearing and lens awareness

Question 9

Large lenses can be particularly problematic when associated with?

Answer 9

high Rx due to thick centre or edges

Question 10

What are the typical TD/OZ combinations?

Answer 10

<9.00mm (7.0)
9.0-9.3mm (7.5)
9.5-9.8mm (8.0)
>9.8mm (8.5)

Question 11

To counteract the BC becoming steeper when increasing TD, what should happen to the BC for every 0.5mm increase in TD?

Answer 11

BC should be made 0.05mm flatter (0.25D)

Question 12

increasing/decreasing TD makes the lens steeper/flatter causing changes in power. What rule is used to help counteract this?

Answer 12

SAM FAP

steeper add minus, flatter add plus

Question 13

increasing/decreasing TD also has an effect on what other fitting characteristic?

Answer 13

edge lift
increasing TD = increase edge lift
decreasing TD = decrease edge lift

Question 14

Summarise the effects of a large lens (5)

Answer 14

• fit more tightly
• move less
• can have higher edge lift
• can have more lid attachment
  generally more stable

Question 15

Summarise the effects of a small lens

Answer 15

• fit more loosely
• move more
• can have lower edge lift
• can have less lid attachment
  generally less restrictive to tear flow and oxygenation

Question 16

What parameter has the most influential change on edge lift?

Answer 16

changing SCR

Question 17

ideal edge lift width?

Answer 17

0.3-0.5mm

Question 18

How can you modify a high plus power RGP to counter inferior decentration?

Answer 18

add minus carrier on edge

Question 19

how can you modify a high minus power RGP to counter lid interaction problems?

Answer 19

add plus lenticular –> wedge shape

Question 20

Why is PMMA a good material to use as a trial lens? (3)

Answer 20

• scratch resistant and machineable

- has no surface charge

Question 21

When would you consider a lower Dk RGP material? (2)

Answer 21

• to reduce surface deposits

- to reduce flexure

Question 22

Dimple veiling etiology, signs and management

Answer 22

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

Question 23

Corneal warpage etiology, signs, symptoms, management

Answer 23

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

Question 24

Peripheral corneal staining (3 and 9 o’clock) etiology, signs, symptoms, Mx

Answer 24

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

Question 25

Dellen signs, symptoms, etiology, mx

Answer 25

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

Question 26

Vascularised limbal keratitis signs, symptoms, etiology, Mx

Answer 26

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

Question 27

RGP induced ptosis signs, etiology, Mx

Answer 27

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