Pre-Fitting Examination
A complete exam should be performed including a thorough slit lamp exam and topography. The progression of the Keratoconus will determine the first lens to select during the trial lens fitting. Typically an emerging cone will show minimal physiological and topographical keratoconic signs. As the condition progresses distinct physiological signs such as "Munson's ring", thinning of the cornea, corneal scaring and increased cornea distortion will become present. These findings should be noted at the initial fitting.

Selecting Lens Size
Lens diameter is determined by the severity of the cone progression. As a rule of thumb, the steeper the cone the smaller the lens. Typically, a 9.0 mm lens will be used on most corneas while a 8.4mm lens will be used on a more advanced cone. Custom diameters are available on special request.

Base Curve Selection
The initial base curve trial lens is determined by evaluating the patient's corneal topography. It is important to note both the "sim "K" and the color map itself. Attention should be given to how steep the cornea is at its steepest area. An average of the total corneal cylinder should be done. This average is determined by subtracting the flattest "sim K" from the steepest area on the color map. It is important to read the color grid accurately in order to determine the absolute steepest area of the cornea. Once that difference is determined, divide that number by 3 and add the answer to your flat "sim K" for your initial base curve trial lens. A properly fit base curve will have light central touch with some touch points in the mid-periphery. Once you determine base curve check the periphery.

Peripheral Fit
Trial lenses have a standard edge lift, but an increase or decrease edge lift can be ordered. The proper edge lift should show a least .5 mm of fluorescein the periphery of the lens. If the base curve looks good but the periphery is inadequate then order a flatter edge lift. Conversely, order a decrease edge lift if the periphery looks too flat.

Physical Fit And Fluorescein
A properly fit lens should move on the cornea and routinely exhibits a fluorescein pattern with three points of touch. Caution should be taken not to have a lens that shows 360 degrees of bearing. This will cause seal off and result in a lens that fits too tight. The lens should lightly touch centrally and in the mid-periphery. If your trial lens shows central touch with 360 degrees of seal off order a lens with a flatter edge lift or fit the same lens in a smaller diameter. If your trial lens shows heavy bearing go to a steeper lens; if it shows heavy central pooling go flatter.

Power Determination
The power of the lens should be determined by over refracting a properly fitting trial lens.