Which keratometry measurement defines the 'on K' nomogram?

Which keratometry measurement defines the 'on K' nomogram?

• A. off K
• B. average K
• C. central K reading
• D. on K

Answer: (D)

In this context, the approach called on-K means you base the base curve decision on the keratometry value that reflects the cornea’s curvature measured by the keratometer. The lens is intended to sit on the cornea, so the reference point for selecting the initial base curve is the keratometer’s reading itself—the on-K measurement. That’s why this nomogram is defined by the keratometry measurement labeled on-K. Using an off-K approach would involve adjusting from that keratometry value (an offset), while using average K would reference the mean curvature across the cornea rather than the specific on-K reference, and a central K reading is just a single keratometry value rather than the working reference for the on-K method.

In this context, the approach called on-K means you base the base curve decision on the keratometry value that reflects the cornea’s curvature measured by the keratometer. The lens is intended to sit on the cornea, so the reference point for selecting the initial base curve is the keratometer’s reading itself—the on-K measurement. That’s why this nomogram is defined by the keratometry measurement labeled on-K.

Using an off-K approach would involve adjusting from that keratometry value (an offset), while using average K would reference the mean curvature across the cornea rather than the specific on-K reference, and a central K reading is just a single keratometry value rather than the working reference for the on-K method.