KeraKone is a multi-spherical back surface Keratoconus lens and 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.
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
toricityto 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
- 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
- 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
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)|
Why KeraKone 2?
- Suitable for all keratoconic profiles
- Aberration control optics providing excellent visual acuity
- Reduced flare and glare
- Extensive base curve and diameter range
- Familiar fitting strategy
Firstfit for irregular corneas such as KC and Post Lasik Ectasia
- Refits from other leading designs
- When soft KC lenses are no longer adequate
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|
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