When selecting a GP lens, the most important aspect is the appropriate sagittal depth, which is influenced by:

• A. lens color
• B. power
• C. appropriate sagittal depth (both base curve and diameter impact sagittal depth)
• D. edge design only

Answer: (C)

The key idea is that the fit of a gas-permeable lens hinges on sagittal depth—the amount the lens vaults over the cornea. This sagittal depth is set mainly by two parameters: the base curve and the overall diameter. The base curve determines how steeply the lens’ posterior surface sits against the cornea; a steeper base curve increases sagittal depth, while a flatter one decreases it. The diameter works with the base curve to shape how the lens vaults across the central and peripheral cornea, influencing edge lift and overall sagittal height. Color has no effect on this fit, and while power relates to refractive correction, it doesn’t determine sagittal depth by itself. Edge design matters for comfort and movement, but the primary drivers of sagittal depth are the base curve and diameter. That’s why the best choice is the statement that sagittal depth is influenced by both base curve and diameter.