Due to the variations in Keratoconus, no one fitting regime is perfect for all cases.

Custom have been involved with Keratoconus for many years and we find that the following 3 types of fitting will work well if correctly applied for this type of patient.

Standard RGP Keratoconus lenses with diameters from 8.80  mm to 10.20 mm and base curves from 5.50 mm and up will fit for most early to middle stage keratoconus with reasonably centred cones. The problems arise for decentred cones, especially from PMD in which the cone is low and nasal or low and temporal, these require assistance to help with lens centration (Piggy back with groove)  or better still to vault the cornea using  the Stoker semi scleral lenses (13.50 or 14.50mm diameter) These are proven designs used for more than 20 years with an extremely high success rate. 

All the above types of lenses must be fitted from a diagnostic set, which is available from Custom on loan or can be purchased.

Note no 2 keratoconus patients are the same so you must be flexible in your fitting to maximise comfort and vision for your patients.

 

Do topography and note the centre of the cone. Note K readings and corneal height. Utilising the Topographers features look at the 3 D image. Next look at the fourier images for irregular astigmatism.

From the above you can feel confident in knowig the stage of the 'cone. If early to mid then utilising the standard Custom diagnostic set, fit a lens which you feel should be good. Check the fluoresceine image with the lens centred on the cornea, and assess if too steep or flat. If the picture shows excessive touch (note you will see the apex of the cone quite clearly) then go 2 or 3 steps steeper and repeat. When you just get clearance then go back (ie flatter) by one step. This should be the optimal base curve. Note the position of the lens and the amount of edge stand off. Over refract this lens and order, adjusting the edge lift as required. (increase for more edge lift and decrease for less.)

For better centration you can go larger in diameter or if dealing with tight lids smaller.  Adjust the base curve accordingly.

Note it may take more than one lens to obtain the optimum fit.

I find that if a patient is shown the topography, they get a better understanding of their problem and the complexities involved in the fitting.

If the 'cone is well off centre then consider going to a Soft lens Piggy back, (Our lens has a groove to hold the lens centred) or consider a Stoker Semi scleral design (my preference)