Soft contact lens fitting

Parameters
Fitting advice
Multifocal
Observation

Diameter and Base curve choice for the first contact lens

  1. Measurement of the corneal diameter (HVID + 0.6 mm)* and K-readings. Note: 80% of the corneal diameters are statistically between 11,3 and 12,1 mm
  2. Determine the contact lens diameter ØT
  3. Determine of the Base curve r0 = rcfl + BCf (rcfl = flattest central K)

Example: Parameter for Toris Ballast

Cornea parameters: ØCornea = 11.70 mm / Kreading = 7.80 / 7.70 mm

  • ØT = 11.70 mm + 2.30 mm = 14.00 mm
  • r0 = 7.80 mm + 0.70 mm = 8.50 mm
  • for 0.40 mm delta K, reduce 0.10 mm on r0
  • Definitive 74: 0.10 mm steeper

Progress of the adaptation

  1. Insert trial lens for a duration of between 30 minutes and 2 hours. Over refraction (you can use the autorefractometer for getting an idea of cyl/axis).
  2. Biomicroscopy (× 10 to 15) white light: observe the lens with patient looking straight ahead and during eye movement.
  3. Mobility by eyelid movement, (Push up test).
  4. Sag of the lens should be from 1 to 2 mm downwards.
  5. Appearance of the front optic zone: tear film, hydration, lubrication, deposit.
  6. Keratometry on the contact lens: (deformation of the mires).
  7. Check for corneal and conjunctival staining with fluorescein after lens removal.
  8. Order the definitive lens on the basis of the SN.

Multifocal soft contact lens fitting advice

Progression system and central optic zone (Zoc)

Reading zone choice

  1. Centre near vision in most cases
  2. Peripheral near vision if distance vision is poor, high myopia or decentrated pupil

Procedure

  • Determine dominant eye
  • Find maximum convex (+) correction for distance vision
  • Find the best acuity in distance vision to optimise Zoc diameter choice
  • Determine the patients needs for: distance / intermediate / near

Multifocal design choice


Requirements Bf Bifocal Sp Simple progressive Mp Multi progressive
Hyperopia
Myopia Addition < 1.75 dpt.
Myopia Addition ≥ 1.75 dpt.
Priority in distance vision
Priority in near vision
Priority in intermediate vision (computer)
Use in low light in distance vision
Use in low light in near vision
Good contrast
Low Halos
Anisometropy > 2.00 dpt
Amblyopia (√)
Modified monovision care (√)

Central optic zone, position and diameter: recommendations for the 1st choice:

standard pupil (3.50–4.00 mm) with normal lighting


Position Bf center near Bf center distance Sp center near Sp center distance Mp center near
Dominant eye 2.25 3.75 2.50 4.00 1.50
Non-dominant eye 2.75 3.25 3.00 3.50 1.75
Undefined 2.50 3.50 2.75 3.75 1.5

For non standard pupil size or for distance/near preference, fit the Zoc in steps of 0.25 mm


Observation

Primary Position

Upward Position

Nasal Position

Good Fit

  • Comfortable
  • Good centration with full coverage of limbus, even in upward gaze and vertical movments
  • Adequate smooth movement in all directions of gaze of 1- 2 mm
  • Good recovery on push-up test
  • Reasonable over-refraction

good_primary-position good_lens-up-position good_lens-nasal-position

Flat Fit

  • May give poor centration
  • Contact lens drops down > 2 mm
  • Contact lens follow not the eye movement, or delayed
  • May give unstable vision
  • Can cause discomfort
  • Try steeper base curve (If available)
  • Non-reasonable /Fluctuating over-refraction (after blinking bad->good)

flat_lens-position flat_lens-up-position flat_lens-nasal-position

Steep Fit

  • Displays inadequate or no movement < 1 mm
  • Resists push up test with lower lid
  • Contact lens stay centred on cornea with eye movements
  • Can cause blanching
  • Non-reasonable /Fluctuating over-refraction (after blinking good -> bad)

steep_lens-position steep_lens-up-position steep_lens-nasal-position