Which practice best aligns with predicting GP lens power when tear layer considerations are used?

• A. Start with sphere; if unable to obtain BCVA.
• B. Use a predicted lens power that accounts for tear layer.
• C. Rely only on keratometry.
• D. Adjust by trial and error without tear layer.

Answer: (B)

Accounting for the tear layer is essential because the tear film between the cornea and the back of a GP lens acts as its own refracting surface and changes the eye’s overall optical power. Keratometry only measures the anterior corneal curvature and ignores this tear lens, so a power estimate based on keratometry alone will be off once the tear layer is in place. Using a predicted lens power that includes tear layer effects gives a more accurate starting point and reduces the need for multiple adjustments.

Relying solely on keratometry or adjusting by trial and error without considering the tear layer both miss this crucial factor, leading to less predictable vision and more fitting cycles. By incorporating tear layer considerations into the initial power prediction, the GP lens is better positioned to provide the desired refraction from the outset.