1. Refract patient (convert to minus cylinder if necessary).

  2. Obtain Keratometry readings.

  3. Select B - Design trial lens closest to flat "K."

  4. Over-regract patient.

  5. Adjust base curve of lens to be ordered.

Final RGP Rx should be the sphere power (adjusted for vertex) of patient's spectacle Rx.


"K"​  43.25 / 44.00

Rx  -2.00 -1.00 x 180

Trial B - Design  43.50

Over Refraction  -2.25

Final Lens Rx  43.25 -2.00 9.0

Using the B – Design system you can see that this patient had an over-refraction of -0.25 stronger than their spectacle Rx caused by a tear lens of +0.25 so you would flatten the base curve and keep the Rx the same as their spectacle Rx.

Minus over-refraction = flatter base curve

Plus over-refraction = steeper base curve