How do we measure corneal shape during GP lens pre-fit assessment?

• A. Slit-lamp examination only
• B. Wavefront aberrometry only
• C. Ultrasound pachymetry only
• D. Manual keratometry, stimulated keratometry, auto-keratometry, topography

Answer: (D)

Measuring corneal shape for GP lens pre-fit requires getting accurate data on the anterior corneal curvature, since the base curve and overall fit of a GP lens depend on how steep or flat the cornea is and where curvature varies across the surface. Manual keratometry, stimulated keratometry, auto-keratometry, and topography together provide that information. Keratometers (in its manual, stimulated, and automated forms) quantify curvature along meridians and give radii of curvature that guide base curve selection. Corneal topography expands on this by mapping curvature across the entire corneal surface, revealing mean curvature, astigmatic axis, and any irregularities or localized steepening that might affect fit or lens optics.

Slit-lamp examination can show surface quality and health but doesn’t supply reliable numerical curvature data. Wavefront aberrometry analyzes optical aberrations rather than direct corneal shape, and ultrasound pachymetry measures corneal thickness, not curvature. Therefore, relying on a combination of keratometry measurements plus topography provides the most complete and actionable picture of corneal shape for GP lens pre-fit.