5.3.3. Understands the techniques used in the fitting of complex contact lenses and advises patients requiring complex correction.

Question 1

correcting: High anisometropia / ametropia

Answer 1

• Ideal form of correction & may give better VA / reduce issue of aniseikonia as no magnification / minification effect
• SCLs
  o Use SiHy with a high Dk/t due to thick lens and use a large lens for stability.
  o Ensure strict replacement schedule, particularly if EW.
  o Mark ennovy for specialist lenses – weekly/monthly/3 monthly custom lenses
• RGPs
  o Large diameter for stability
  o High plus RGPs have a centre of gravity which is further forward, so need to check fit in something close to px’s actual Rx, as just using a standard +3.00 fitting set will not give an accurate representation of how the high plus lens will sit

Question 2

Aphakia

Answer 2

 High + lens with SiHy / large diameter RGP c UV filter

Question 3

Keratoconus

Answer 3

• Non-inflammatory progressive ectasia of the cornea causing an irregular thinned corneal appearance; due to collagen disorder
• Late teens/early twenties; bilateral but often asymmetric
• Risk factors: eye rubbing, atopy, higher incidence in Asians, familial link, systemic disorders
• Presentation: blurred vision, frequent rx changes (myopia/astigmatism), glare
• Signs: scissor reflex on ret, oil droplet reflex on ophthalmoscopy, Munson’s sign (cornea protruding forward), mod-high degrees of myopia/astigmatism, low CCT, irregular mires/topography, striae in posterior stroma
• Tx; corneal cross-linking done as soon as possible (routine referral) – UV light to strengthen bonds between collagen fibres of cornea

Question 4

TX of keratoconus based off of stages

Answer 4

• Early stages may be able to correct with softs e.g. kerasoft
  o Front surface aspheric/aspheric toric
  o Large back optic diameter to allow full drapage
  o Adjustable periphery fits any corneal shape
• Standard RGPs can be used in early stages
  o 3 point touch fitting technique: apical bearing & two other points of mid peripheral touch 180 degrees apart
• More advance stages may require specialist lenses
  o Rose K – smaller BOZDs to better fit the cone curvature
  o Piggy back RGPs; RGP over plano CL to improve comfort & centration
  o Hybrid lenses; RGP centre with soft outer skirt
  o Semi-scleral; large diameter (14-16mm) RGP, vault whole cornea
  o Scleral lenses; 18-23mm

Question 5

Post-surgical

Answer 5

• Be aware of abnormal corneal shape, may require topography.
• Corneal grafts tend to be slightly nasal, and so the CL will be centred slightly nasally.
• Abnormal NaFl patterns.
• May fit large diameter bandage CL on leaking bleb following trabeculectomy.

Question 6

Post-LASIK

Answer 6

• May fit normal CL, try it & see - more likely to be successful if pre-LASIK Rx was fairly low. If Rx was more than -10.00DS then >100um of stroma was removed, and a reverse geometry lens may be required (as standard RGP will give central pooling).

Question 7

High Ametropia

• ± 10.00D or above
  
  • What potential problems in specs?

Answer 7

• Unilateral —> anisometropia, aniseikonia
• Plus lenses —> magnification, ring scotoma
• Minus lenses —> minification, peripheral ghosting
• General —> lens weight, cosmesis, cost
• Possible need for lentics?
• High index = lower V value = more dispersion = fringing
  BVD

Question 8

High Ametropia

Hypoxia Biggest Issue

Answer 8

• RGPs - best option for maximum visual correction (and best tear flow). Hypoxia not as much of issue.
  
  • Lenticular and single-cut designs
    
    • Lenticular has minus lens carrier with big positive centre. Carrier for better lid hitch. Can be ordered without carrier.
      Single cut = like lenticular. Very curved design so heavier and more prone to decentering.
• Silicone hydrogels – lense becomes thicker at high power but still good Dk/t
• High water content hydrogels (close monitoring needed)

Question 9

High Ametropia

Types of Lenses:

Answer 9

• Mark’ennovy (VERY EXPENSIVE!!!) reusable sphere goes from -30D to +30D with diameters from 13-16 in 0.50mm steps. Resusable toric goes to 30D with 8D max of cyl
• No7
• Bioinfinity reusable sphere goes from +15D to -20D
• Proclear reusable sphere goes up to +/- 20D

Question 10

High Ametropia

Fitting

Answer 10

• Larger TD (~0.5mm larger than usual) (helps centering)
• Fit on mean K (better apical clearance)
• Lid hitch (lens then stays where it should even on blink otherwise lens goes all the way down on blink and so optic zone not centered!)
• Reduced optic (reduced weight of CL as a result, as smaller region in centre that normally holds that thick portion in place. Reducing weight = more lid hitch and better centering)

Question 11

High Ametropia

Fitting

Answer 11

• Larger TD (~0.5mm larger than usual) (helps centering)
• Fit on mean K (better apical clearance)
• Lid hitch (lens then stays where it should even on blink otherwise lens goes all the way down on blink and so optic zone not centered!)
• Reduced optic (reduced weight of CL as a result, as smaller region in centre that normally holds that thick portion in place. Reducing weight = more lid hitch and better centering)

Question 12

Infant Aphakia

Answer 12

• Absence or loss of the lens can occur due to:
  
  • Congenital cataracts - 3-4/10,000 live births, 40-50% unilateral
  • Trauma
  • Lens subluxation - Marfan’s syndrome
• Rapid change in ocular dimensions
  
  • Average corneal radius of curvature in new-born = 6.9mm, flattening rapidly in 1st 6 months
  • Axial length of 17mm —> 21mm over first 6 months of life
  • Aphakic Rx approx +25DS —> +15DS in first few years of life
    
    • Spex/CLs require very frequent changes

Question 13

Advantages/ Disadvantages of Spex wear:

Answer 13

• Advantages of Spex wear:
  
  • No risk of infection
  • Well tolerated
• Disadvantages of Spex wear:
  
  • Challenging in unilateral cases
  • Expensive & easy to break
  • Cosmesis worse
  • Heavy
  • Peripheral distortions

Question 14

Advantages/ Disadvantages of CL wear:

Answer 14

• Advantages of CL wear:
  
  • Not heavy
  • Easier for patients once inserted
  • Cosmesis better
• Disadvantages of CL wear:
  
  • Risk of infection if cleaning regime not followed
  • Challenging for parents

Question 15

Initial scleral lens choice

Answer 15

• SiH, 3/12 replacement, some available in wide range of parameters (up to +50DS), Ultravision CLPL
• Advantages: increased modulus, better stabilising, reduced hypoxia

Question 16

Why IOLs are not commonly used?

Answer 16

• The human eye usually experiences 3–4 mm of axial elongation during the first year of life. Concurrently, the cornea and crystalline lens flatten, resulting in a relatively stable refractive error. The myopic shift induced by axial elongation following infantile cataract surgery cannot be fully offset by corneal flattening resulting in overall myopic shift. In aphakic eyes, the myopic shift can easily be corrected as needed by reducing the power of corrective contact lenses or spectacles. Similarly small myopic shifts can also be corrected with contact lenses or spectacles in pseudophakic eyes. However large myopic shifts may necessitate an IOL exchange
• IOL also can’t change focus for near tasks for the infant
• Does the IOL become dislodged with growth of the eye overtime?