KeraKone is a multi-spherical back surface design incorporating aberration controlled front and back aspheric optics on the optic zone diameter.

KeraKone is a rigid contact lens for keratoconus that takes advantage of a well-established approach to keratoconic lens fitting through adaptive design and optic zone control.

KeraKone has three standard peripheral systems - STANDARD, INCREASED and DECREASED. These three options should fit the majority of keratoconic patients.

To download the KeraKone fitting guide click here

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 3: 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 4: Excessive Edge Lift

Figure 5: Inadequate Edge Clearance

Fig. 4 and Fig. 5 courtesy of Keith Tempany FBDO CL FBCLA.

Design Number of Lenses BCOR Diameter Power
KeraKone 24 5.10 to 7.40mm (0.10mm steps) 8.70mm -23.00 to -2.00D (in 1.00D steps)
  • Easy-to-fit using a simple, systematic approach for all keratoconic patients that reduces chair time
  • Fits all corneal shapes, sizes and stages of keratoconus because of the unique design that changes as the base curve steepens
  • Simple to use flexible edge lift system
  • Aberration control aspheric optics providing outstanding visual acuity, reduced flare and glare and minimum lens mass
  • Extensive diameter and base curve range
Design KeraKone
Material Optimum and Boston
DK Dependent on material
Tint Dependent on material
Base Curve 4.50 to 7.50mm in 0.05mm steps
Diameter 8.70mm (standard), 8.10mm, 8.40mm, 9.00mm, 9.30mm
BVP +25.00D to -25.00D
Edge Profile Standard, 2 steps available flatter and steeper

Click to enlarge image

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