If we fit a GP lens flatter than K with a minus tear layer, this will require more plus or minus to neutralize? (SAM FAP)

• A. Minus tear layer (SAM FAP)
• B. Zero tear layer (SAM FAP)
• C. Plus tear layer (not SAM FAP)
• D. Plus tear layer (SAM FAP)

Answer: (D)

When a GP lens sits flatter than the cornea (flat relative to keratometry), the tear film that fills the space between the posterior lens surface and the corneal surface forms a lens of its own. The sign of that tear lens depends on how the lens sits: a flatter fit tends to create a tear layer with minus power, which makes the overall system less convergent than the cornea alone.

To bring the eye back toward the target refraction, you must offset that minus tear lens by adding more plus power to the overall optical setup. In the SAM FAP framework used here, that compensating tear layer is described as a plus tear layer. So, when the lens is flatter than K and the tear layer is minus, neutralizing the effect requires plus power, corresponding to a plus tear layer (SAM FAP).