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

Question 1

High anisometropia / ametropia best CL options:

Answer 1

• Ideal form of correction & may give better VA / reduce issue of aniseikonia as no magnification / minification effect
  SCLs
• Use SiHy with a high Dk/t due to thick lens and use a large lens for stability.
• Ensure strict replacement schedule, particularly if EW.
• Mark ennovy for specialist lenses – weekly/monthly/3 monthly custom lenses

RGPs
* Large diameter for stability
* 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 best CL option

Answer 2

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

Question 3

Keratoconis: Define

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

Keratoconus RGP lens type:

Answer 4

• Early stages may be able to correct with softs e.g. kerasoft
  1. Front surface aspheric/aspheric toric
  1. Large back optic diameter to allow full drapage
  1. Adjustable periphery fits any corneal shape
• Standard RGPs can be used in early stages
  1. 3 point touch fitting technique: apical bearing & two other points of mid peripheral touch 180 degrees apart
• More advance stages may require specialist lenses
  1. Rose K – smaller BOZDs to better fit the cone curvature
  1. Piggy back RGPs; RGP over plano CL to improve comfort & centration
  1. Hybrid lenses; RGP centre with soft outer skirt
  1. Semi-scleral; large diameter (14-16mm) RGP, vault whole cornea
  1. Scleral lenses; 18-23mm
  1.

Question 5

High Ametropia

What potential problems in specs?

Answer 5

• 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 6

High Ametropia

Biggest issue with high rx lens?

Answer 6

• Hypoxia Biggest Issue
  
  • 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 7

High Ametropia

Types of Lenses:

Answer 7

• 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 8

High Ametropia

Fitting rgp

Answer 8

• 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 9

Infant Aphakia

Absence or loss of the lens can occur due to:

Answer 9

• Congenital cataracts - 3-4/10,000 live births, 40-50% unilateral
• Trauma
• Lens subluxation - Marfan’s syndrome

Question 10

Infant Aphakia

Rapid change in ocular dimensions is important?…

Answer 10

• 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
  • Remember that the cornea accounts for 2/3 of the focussing power & it has an average of 43D. The lens is 1/3. Half of 43 will be the average lens focussing power i.e. 21.5D. Of course, this is only an average & varies depending on corneal curvature. Therefore, high Rx needed for aphakia.

Question 11

Advantages vs disadvantages of spex in infants:

Answer 11

• 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 12

Advantages vs disadvantages of cls in infants:

Answer 12

• 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 13

Infant Aphakia

Why IOLs are not commonly used?

Answer 13

• Because of axial elongation in first year, cornea and lens faltten, resulting in stable rx. Myopic shift in cataract surgery cannot be fully offset by corneal flattneing resulting in myopic shift, vs easily corrected by reducing [pwer of refractive lenses or spectacles
• IOL cannot focus on enar tasks for infants

Question 14

Which is more important when it goes to Dk with RGP vs scleral lenses?

Answer 14

GP lenses don’t cover entire cornea & so oxygen still being supplied to other parts of cornea due to atmosphere & not by relying on the lens, in addition to the tear exchange underneath it which also helps. With scleral, it covers the whole cornea & tear reservoir is more important therefore high DK needed (100+) whereas GP can be <100.

Question 15

Indications for Sclerals:

Answer 15

Corneal cyls
* Patients where soft toric lenses show unstable
rotation
* But RGPs are uncomfortable
* Particularly true of moderate to high cyls
Presbyopes
* Particularly astigmatic presbyopes

Question 16

Sag Fitting: Between lenses?

Answer 16

• RGP lenses are fitted by curvature - match shape of cornea
• If vaulting, curvature not as useful to use. For example, a steep cornea will have a shallow vault
• Sclerals are fitted by vault or sag, in microns

Question 17

Central Clearance: Scleral

Answer 17

• Fully clears cornea, target is 200-300 microns.
• Use wide beam & blue light to initially see no corneal contact.
• Then, use narrow beam & white light to better assess clearance
• If there is touch, go for deeper lens

Question 18

Scleral lenses: Complications

Answer 18

Conjunctival Prolapse
* Conjunctiva ‘sucked’ up under lens to cover
limbus
* Can be in anymeridian
Deposits - Progent good as it chemically cleans lenses
Excessive settling back - use larger lens
Fogging - fluid reservoir goes cloudy
- Px has to remove & refill
- Worse in first month or so but patient adapts
- Don’t over vault the limbus & peripheral cornea
- Experiment by filling lens with artificial tears - 50/50 saline & tears. Up the tears if this doesn’t work

Question 19

keratoconus signs, early vs moderate vs advanced

Answer 19

• Signs (early)
  
  • Asymmetric Rx with high cyls (progressive) - frequent spex changing
  • Steep K’s (progressive) - worth measuring each visit
  • Scissor & oil drop on ret
  • Prominent corneal nerves
• Signs (moderate)
  
  • Vogt’s striae - put little pressure globe & should disappear (vertical lines in the posterior stroma of Descemet’s membrane)
  • Munson’s sign - down gaze on slit lamp
  • Fleischer’s ring - ring caused by iron deposits at base of cone in epithelium but another type is Keiser ring caused by copper deposits —> sign of Wilson’s disease
• Signs (Advanced)
  
  • Extreme corneal thinning
  • Stromal scarring (following hydrops)

Question 20

Keratoconus: When to fit wht CL?

Answer 20

Poor spectacle VA from irregular astigmatism caused aberrations and haloes

Question 21

Fitting and eye with keratoconus:

Answer 21

• Early: Soft torics or spherical RGPs (e.g. Kerasoft IC, Ultravision)
  Moderate: Aspheric or bi-elliptical lens design (e.g. Quasar K, No7)
  Advanced: Special keratoconic designs (e.g. Rose K, Menicon)
• CL needs to vault apex of cone!
  
  • 3 Point Touch
    
    • Aim to distribute weight of lens across cone and peripheral cornea
      Divided support:
      2-3mm apical touch (‘feather’ touch)
      Mid-peripheral ring of touch
      Usual edge clearance
    • Most accepted fitting philosophy
    • Particularly good for oval cones
  • Always follow fitting guides! This is especially the case for Rose K lenses

Question 22

Management of Keratoconus summary types:

Answer 22

• CXL - considered if CCT above 400 micrometres!
• Intacs - Little corneal, stromal ring segments to create incision and creating channel going all the way around. Corneal ring flattens steep cones to get CLs in better & potentially improve vision. Implanted into the corneal stromal tunnel created by mechanical or femtosecond laser techniques.
• PK - PK is a full-thickness transplant procedure - only if prev graft fails; last resort!
• DALK - DALK (Deep anterior lamellar keratoplasty) is a partial thickness graft that preserves the TWO inner most layers of the cornea: Descemet’s membrane and the endothelium. The goal of the procedure is to retain the endothelial layer of the host.
• Piggyback lenses - RGP worn on top of soft CL for better comfort if non tol to RGPs or persistant staining after adaptation period to RGPs. Must make px aware of increased risk of infection from piggyback. Must use dd lenses & if possible, NaFL with higher molecular weight to assess
• Kerasoft - front surface aspheric with peripheral curves to adjust to corneal shape. Good for early KC or pxs intolerant to RGPs
• Hybrid - Elements Hybrid (No7); RGP centre with soft skirt, RGP portion: crisp, stable vision
  Soft skirt: comfort, centration and overall wearability
• Corneo-scleral - Good for non tol RGP wearer, aim for 0.2 mm on blink. 1.5-2.0mm of mid peripheral corneal clearance & 1.0-1.25mm scleral coverage

Question 23

Post-surgical for keratoconus?

Answer 23

• Eye is too vulnerable so need healing. Need to wait for VA to improve after surgery.
  Basically, wait for consultant to say you can fit. Normally 6-12 months after surgery
  
  • Want to avoid putting lens onto graft-host junction. Want to try RGP with TD of 11-14mm. If soft, then piggyback, kerasoft, hybrid but with O2 as the priority!
  • Will be high corneal astigmatism (>5.00DC), graft may be sunken or protruding or tilted (high cyl)
  • What does graft rejection look like?
• Scleral/Corneo-scleral lenses
• Soft chosen if RGP not tolerated
• Kerasoft IC
• Piggyback

Question 24

Post-refractive

Answer 24

• Bandage contact lens
  
  • Bandage lenses protect the cornea not only from potential exterior sources of injury, but also from a patient’s own eyelids. The shearing effect created by the lids during the blink can inhibit re-epithelialization and cause pain. Use of a bandage lens facilitates corneal healing in a pain-free environment post surgery. Worn normally for 3-4 days after. SiH for EW
    
    • Showering - have to close your eyes really hard
• Reverse geometry
  
  • Flat central portion. Good for sunken (flat) grafts after surgery. Also for ortho K. Must have really high Dk
• Rose K - Complications, how it fits, when to use
• Scleral - universities, HES. You wouldn’t necessarily fit yourself