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Lens slippage is a defect that occurs when the lens moves out of its secure position inside the edging machine while the grinding wheel is cutting the perimeter. This slippage destroys the lens because the final cut shape is incorrect.
read more about eyeglass lens slippage during edging ...The main cause is poor adhesion of the blocking pad. If the pad is old, dirty, or has insufficient adhesive, the rotational force of the grinding wheel can overcome the holding force, causing the lens to slip. Using an incorrect blocking speed is also a factor.
Slippage drastically affects vision quality because it results in the lens being cut off-center. This shifts the optical center away from the pupil, creating unwanted prism and causing eye strain, headaches, and blurred vision for the wearer.
The technician's role is important. They must make sure the lens surface is completely clean before applying the blocking pad. They must also check the clamping pressure to ensure the lens is held tightly during the high-speed grinding process.
When slippage occurs, the lens shape is incorrect, but more importantly, the center of the lens is shifted. Since the optical center determines where light passes straight through, a small shift makes the lens unusable and requires the lab to produce a completely new lens.
No, once a lens slips during edging, the lens shape is ruined, and it must be remade from a new blank.
No, slippage is almost always a failure of the blocking process or technician error, not the lens material.
Yes, if the lens shifts, it can hit the grinding wheel at the wrong angle and cause damage to the machine.
If your lenses are "off-axis" (the astigmatism correction is in the wrong spot), the lens likely "slipped" during the manufacturing process. If you feel dizzy or your vision is distorted in one eye with new glasses, have your provider check the lens axis with a lensometer.
College of Optometrists. Verifying a Prescription (college-optometrists.org). 2024.
The Vision Council. ANSI Z80.1 Standards for Axis (thevisioncouncil.org). 2024.
Review of Optometry. Errors in PD and Axis (reviewofoptometry.com). 2024.
ABDO. Manual Focimetry (abdo.org.uk). 2023.