If we fit a GP lens flatter than the K, a minus/plus tear layer is formed (SAM FAP). What is the tear layer sign?

If we fit a GP lens flatter than the K, a minus/plus tear layer is formed (SAM FAP). What is the tear layer sign?

• A. Plus tear layer (SAM FAP)
• B. Zero tear layer (SAM FAP)
• C. Minus tear layer (SAM FAP)
• D. Unspecified tear layer (SAM FAP)

Answer: (C)

When a GP lens is assessed for fit, the tear layer under the lens shows how the lens relates to the cornea. If the lens is flatter than the cornea (base curve less curved than the cornea, more apical clearance), the tear film between the back of the lens and the cornea ends up with a negative power, which is observed as a minus tear layer sign. This negative tear layer indicates the flatter-than-K fit in SAM FAP terms. Conversely, a steeper lens would produce a plus tear layer, and a perfect match would give little to no tear-layer sign. So the tear layer sign in this scenario is minus tear layer.

When a GP lens is assessed for fit, the tear layer under the lens shows how the lens relates to the cornea. If the lens is flatter than the cornea (base curve less curved than the cornea, more apical clearance), the tear film between the back of the lens and the cornea ends up with a negative power, which is observed as a minus tear layer sign. This negative tear layer indicates the flatter-than-K fit in SAM FAP terms. Conversely, a steeper lens would produce a plus tear layer, and a perfect match would give little to no tear-layer sign. So the tear layer sign in this scenario is minus tear layer.