Diameter and Base curve choice for the first contact lens
- 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
- Determine the contact lens diameter ØT
- Determine of the Base curve r0 = rcfl + BCf (rcfl = flattest central K)
- Orbis (ØCornea + 2.10 mm / BCf = 0.60 mm)
- Toris Bal – Torelis Bal – Borelis (ØCornea + 2.30 mm / BCf = 0.70 mm)
- Toris Int/Ext – Torelis Int/Ext (ØCornea + 2.50 mm / BCf = 0.80 mm)
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
- 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).
- Biomicroscopy (× 10 to 15) white light: observe the lens with patient looking straight ahead and during eye movement.
- Mobility by eyelid movement, (Push up test).
- Sag of the lens should be from 1 to 2 mm downwards.
- Appearance of the front optic zone: tear film, hydration, lubrication, deposit.
- Keratometry on the contact lens: (deformation of the mires).
- Check for corneal and conjunctival staining with fluorescein after lens removal.
- 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
- Centre near vision in most cases
- Peripheral near vision if distance vision is poor, high myopia or decentrated pupil
- 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|
|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||√|
|Anisometropy > 2.00 dpt||√||√|
|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|
For non standard pupil size or for distance/near preference, fit the Zoc in steps of 0.25 mm