For spherical corneas, nomograms start relative to K as:

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Multiple Choice

For spherical corneas, nomograms start relative to K as:

Explanation:
Starting point relative to the corneal curvature is flatter for spherical corneas. This means choosing a base curve that is less steep than the Korneal (K) reading. The reason is to create just enough clearance over the central cornea so a stable tear lens forms and the lens centers evenly without bearing. A flatter base curve gives predictable initial alignment and movement, allowing you to refine the fit by adjusting steeper or flatter as needed based on movement, centration, and tear film. Starting on K would risk a tighter, bearing fit on a uniformly curved surface, and starting steeper would further crowd the apex.

Starting point relative to the corneal curvature is flatter for spherical corneas. This means choosing a base curve that is less steep than the Korneal (K) reading. The reason is to create just enough clearance over the central cornea so a stable tear lens forms and the lens centers evenly without bearing. A flatter base curve gives predictable initial alignment and movement, allowing you to refine the fit by adjusting steeper or flatter as needed based on movement, centration, and tear film. Starting on K would risk a tighter, bearing fit on a uniformly curved surface, and starting steeper would further crowd the apex.

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