Absence of fluorescein in the secondary or peripheral area may be due to the lens sealing off. Carefully note the location, size and persistence of any air bubbles under the lens. A central bubble may indicate that the lens is too steep. Paracentral air bubbles, on the other hand, may indicate that the optic zone is too large. Patience is a virtue in trial fitting You must let diagnostic lenses settle for at least 15 to 20 minutes to avoid fitting errors.
Keratoconic corneas are very pliable, especially if the previous lens was flat.
A lens that looked appropriate at the diagnostic fitting and again on dispensing may look too flat at the progress visit. But you'll compound the error if you simply place another lens on the eye, evaluate it quickly and then reorder. Because you're not allowing the cornea time to recover and the lens time to settle. You may find that new lenses are substantially steeper when diagnostic lenses are given ample time to settle. Diagnostic fitting for a keratoconus patient may take one to two hours to allow ample time for the effects of previous contact lenses to be neutralized.