5.3.3 Understands techniques used in fitting complex CLs & advises pxs requiring complex correction

Question 1

Describe aphakia and contact lenses?

Answer 1

• No crystalline lens due to congenital abnormality or cataract extraction
• High plus lens (soft or hard) with UV filter
• Ultravision Aphakic and Myopic: 3 monthly lens: power range of +/- 45.00D, Base curvature 7-9.8mm, TD 12.5-16mm
• Ultravision Avanti for Astigmatism: monthly lens: power range sph +/- 20.00, cyl 8.00, axis 1 deg steps, add +4.00. Base curvature 8-9.2mm. TD 14-15mm

Question 2

Describe Albinism and contact lenses?

Answer 2

• Transition/tinted CL may reduce light sensitivity

Question 3

Describe therapeutic contact lenses?

Answer 3

• Bandage CL post LASEK, post lamellar graft, collagen cross-linkin or corneal erosions –> extended wear lens is worn.
  These lenses provide comfort and reduce mechanical trauma to the wound
  Hospital: Bausch & Lomb PureVision
  Specsavers: Opteyes/ CV Biofinity plano

Question 4

Describe high or irregular astigmatism and RGP lenses?

Answer 4

• RGP provides better and more stable vision
• Options include RGPs/ small corneal lenses, hybrid lenses, mini scleral, large scleral

Question 5

Describe hybrid contact lenses?

Answer 5

• RGP centre wht SCL skirt
• Good for those who cannot achieve good vision with SCL but cannot tolerate RGP. Irregular or distorted corneas due to grafts or keratoconus.
• Usually very stable on astigmatic eye and so excessive rotation and fluctuating vision not as common
• Replaced every 6 months due to soft outer skirt expiring
• Ultrahealth Synergeyes: 8.4mm central portion size, TD 14.5mm, DK 130 of GP & 84 of SiHy skirt

Question 6

Describe keratoconus and sxs and signs?

Answer 6

• onset in teenage years where collagen disorder of cornea causes peripheral stromal thinning, causing a connical shape
  Sxs: - frequent change in Rx causing increased myopia and astigmatism. -Blurred & distorted vision
• Glare. - Photophobia
  Signs:
• scissor reflex on retinoscopy.
• Steep K readings.
  -High/irregular astigmatic Rx which may be asymmetric.
• oil droplet on ophthalmoscopy
• Vogt striae: vertical stromal stress lines, dissapear with pressure on globe
• Fleischer ring: epithelial iron deposists around base of cone (best seen on cobalt blue)
• Munson’s sign: protrusion of lower lid on downgaze
• Acute hydrops: due to rupture of descemet’s membrane causing influx of aqueous into stroma

Question 7

What is the management of keratoconus?

Answer 7

• fitting CL keeps px from needing surgery
• GP lenses
• Hybrid lenses
• Scleral lenses

Question 8

Describe specialist fitting of CLs for keratoconus?

Answer 8

• No.7 C4/C4 design (Quasark is multi-aspheric lens with rapidly elliptical smooth surface), Menicon Rose K (‘nipple cones’ to eliminate pooling).
• Choose initial BC midway between average & steep K readings to obtain minimal apical touch & clearance
• 3 point touch has apical bearing & 2 other points of mid-peripheral touch usually 180 deg apart
  Ultravision kerasoft: to treat mild keratoconus in early stages: TD 14-15mm, SiHy, disposable or 3/6/9 monthly

Question 9

Describe piggyback RGP lenses?

Answer 9

• RGP over top of soft lens. SCL is used to smooth out surface allowing for better stability & comfort.
  Downside is 2 lenses on top of each other means amount of oxygen reaching cornea is low

Question 10

Describe CLs and refractive surgery?

Answer 10

• type of surg, wound position, corneal shape, reason for fitting, residual Rx error (is it stable), is px waiting for retreatment, irregular topography

Question 11

Describe scleral CLs?

Answer 11

• large diameter RGP, up to 25mm
• rests on sclera & creates tear-filled vault over cornea which provides new refractive surface. Allows cornea to stay hydrated as well as providing clear vision. Extremely stable on eye and do not move around.
  Useful for: - advance irregular astigmatism
• post-refractive surgery
• post-corneal surgery
• pellucid marginal degeneration
• dry eye tx
• non-tol to RPG lens due to lid irritation from lens edge

Sizes: scleral (18-24mm), mini scleral (15-18mm), cornealscleral (13-15mm)

Question 12

Describe mini-sclerals?

Answer 12

• larger than RGP, smaller than scleral
• good for corneal scarring, irregularity and dry eyes
• B&L Zenlens is v popular in hospitals and usually 1st choice for pxs w/ post surface/refractive surgery or mod-severe keratoconus
  Fitting:
• designed to vault cornea completely
• no contact with cornea means you can minimise scarring, fit irregular corneas and protect cornea surface
• fitted by sag/depth rather than curvature
• lens should clear entire cornea and limbus. Full bearing and touch of lens should be on sclera
• lenses fitted from fitting set, initial lens calculated based on topography & OCT or can be chosen based on tables according to condition
  Insertion: lens filled with saline solution, look down holding both lids and place lens directly on eye

Question 13

Describe assessment of mini-scleral lenses?

Answer 13

• fitting charatacterised by 3 zones: central clearance, limbal clearance and scleral landing
• Central Clearance Zone: lens needs to be clear by 300-400 microns. Can’t use NaFl staining. Check if iris and pupil is visible (if visible there is inadequate clearance). Compare thickness of lens (350 microns) to thickness of tear lens. Should be 1:1 ratio - cannot compare cornea as in keratoconus cornea is thinner at apex, need to ensure clearance over entire cornea. Clearance needs to be accurate at time of fit due to settling of lens into conjunctiva (sinks by approx 100-150 microns).
• Limbal Clearance Zone: NaFl should bleed out from centre to conj (observe in white light). Essential to maintain corneal health. Inadequate clearance will lead to staining and discomfort. If limbal touch increase limbal angle.
• Scleral Landing Zone: sclera is supporting entire weight on lens, its landing needs to be smooth and not impinging any vessel. Trace vessels to check for this. If vessels blanch then most likely being impinged.
• Removal: massage in an inferior bubble, scissor technique
• Care regime: soft lens solutions (not GP), non-preserved saline, alcohol based cleaner

Question 14

Describe corneosclerals?

Answer 14

• Aim to distribute weight and pressure evenly across cornea and sclera, much closer fit
• Thin NaFl central, MP and limbal clearance and sclera landing
• Lens marked with BC and sag (normal px fit flattest K, KC px fit 3 steepest BC)
  Fitting: - lens too deep/steep - central bubbles and pooling, scleral infringement (move to flatter lens).
• lens to shallow/flat - stand off edge, central corneal compressing (move to steeper lens)
• Peripheral standoff - pooling on edge & increased lens awareness, lids catching lens
• Limbal clearance - once peripheral curve and sag is set - adjust limbal clearance by altering central curver only - flatten gives greater clearance w/o changing sag. Limbal touch causes adherence, staining, poor comfort and lack of tear exchange.
• Excessive clearance may cause central staining & bubbles in limbal area.
• Fitting KC a lens whic vaults cornea and no heavy contact apex or at limbus. Sub optimal acuity may opt for flatter fit but increases possibility of scarring (mini-scleral is best)

Question 15

What is fenestration with CLs?

Answer 15

small hole which helps lens settle easier, allows easier removal of lens (forms bubbles)