In an ideal GP lens fit, how much movement is expected?

• A. 0 mm
• B. 4-5 mm
• C. 1-3 mm
• D. 5-6 mm

Answer: (C)

Movement with each blink is essential for a healthy GP lens fit. Gas-permeable lenses sit on a thin tear film, so a little movement shows there’s adequate tear exchange and proper tear film dynamics under the lens. In an ideal fit, the lens should shift a modest amount on the eye—approximately one to three millimeters with a blink. This range provides enough mobility to maintain comfort and tear exchange while keeping the lens well-centered. If there’s no movement, the fit is too tight and tear exchange is limited; if movement is excessive, the lens is too loose and stability and comfort suffer. So, about 1–3 mm of movement reflects the best balance for a well-fitting GP lens.