If the center of gravity of a GP lens is more posterior, centration tends to be better. True or False?

• A. True
• B. False
• C. Depends on lens diameter
• D. Depends on pupil size

Answer: (A)

The way a GP lens sits on the eye is influenced by how its weight is distributed. If the center of gravity is more posterior, gravity tends to pull the lens so that its heavier mass sits toward the back, which helps the lens settle more evenly over the central cornea. This stabilizes the contact with the corneal surface and reduces the tendency for the lens to ride toward the edge, so centration stays better.

If the center of gravity were more anterior, gravity would pull the lens forward, making it more prone to edge lift and decentration due to eyelid and tear-film interactions during blinking. So, a posteriorly located center of gravity promotes better centration.