LINK

Aims and Ideal Fit

• The aim of fitting KeraKone is to fit a lens which provides good acuity whilst being comfortable and maintaining corneal integrity.
• The ideal fit (Fig. 1) will have:
  • Light feather touch at the apex of the cone
  • A small amount of apical clearance is acceptable
  • As close to alignment as possible over the cornea
  • Edge clearance producing a fluorescein band of 0.5 to 0.8mm.
  • Good centration

Figure 1 – Ideal Fit

Trial Lens Selection

• Topography fitting:
  • Start with a trial lens which has a base curve close to the measurement at the temporal 4mm position
• Keratometer fitting:
  • Start with a trial lens 0.20mm steeper than mean K

Fitting and Troubleshooting

• We recommend the use of a short-acting topical anaesthetic to reduce tearing and enable accurate fluorescein assessment.
• After instilling fluorescein, wait at least 2 minutes for the excess fluorescein to dissipate before assessing the fit, or a false fitting pattern may be observed.
• Central fit assessment:
  • Aim for light feather touch at the apex.
  • Excessive apical clearance (Fig. 2) may result in reduced visual acuity; flatten the base curve until very light apical touch can be discerned.
  • Excessive apical bearing (Fig. 3) increases the risk of corneal abrasion and scarring; steepen the base curve until light feather touch is seen.

 Figure 2 – Excessive Apical Clearance

Figure 2 – Excessive Apical Bearing

Peripheral fit assessment:

• There will usually be some toricity to the edge clearance so it should be assessed along both the flat and steep meridians.
• Excessive edge lift (Fig. 4) will result in a lens which moves too freely.
• Inadequate edge clearance (Fig. 5) will be seen as a fluorescein band of less than 0.5mm and a dark ring of touch near the edge of the lens. The lens may be uncomfortable and may not move freely.

Edge profile adjustments:

• Fitting sets are supplied with standard edge lift
• 2 steps of increased and 2 steps of decreased edge lifts are available
• Each increment has been calculated to produce a clear and noticeable change in the fit

Lens Diameter:

• The standard diameter is 8.7
• Lens diameter should only need to be altered in advanced cones or very toric corneas
  • If the lens is riding low, increase the total diameter
  • If the lens is riding high, decrease the total diameter

Lens Power:

• Over-refract initially using 1D steps and then refine using 0.50D and 0.25D steps

Figure 3 – Excessive Edge Lift

Figure 4 – Inadequate Edge Clearance