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An ophthalmic de-centration block is a specialized mounting device used in optical labs during the lens surfacing process. It is used to position the lens blank off-center on the surfacing machine to meet the wearer's precise pupil distance (PD) requirements.
read more about ophthalmic de centration block ...The main function is to align the optical center. Since the lens must be cut precisely for the individual wearer, the de-centration block makes sure the lens is mounted at the correct distance from the machine's center axis, guaranteeing the prescription is centered for the patient's eyes.
De-centration is directly related to the wearer's PD. If the PD is different for each eye (monocular PD), the block is adjusted differently for the right and left lenses. This ensures both lenses are properly aligned to the wearer's unique facial anatomy.
The de-centration block prevents prismatic effect. If the lens is not centered correctly, the wearer looks through an area of the lens that acts like a prism. The block eliminates this error by making sure the lens is ground and finished with the optical center in the correct spot.
The de-centration block shows the level of precision needed in spectacle production. This tool ensures that the optical quality of the finished lens meets the required standard, which is important for comfortable and distortion-free vision.
Yes, the block is designed to be reusable after the finished lens is removed in the deblocking process.
Yes, every spectacle lens must be blocked and mounted using a method that accounts for the wearer's pupil distance.
Yes, positioning the lens off-center can increase the overall thickness of the final lens.
If your pupils are very close together or very wide, the lab must use "de-centration." This can result in one side of the lens being much thicker. If you experience dizziness, the de-centration might be inducing prism; a doctor must verify the optical centers.
The Vision Council. Laboratory Processing Standards (thevisioncouncil.org). 2024.
ABDO. Spectacle Lens Centration (abdo.org.uk). 2023.
Review of Optometry. Errors in PD and Centration (reviewofoptometry.com). 2024.
College of Optometrists. Verifying Spectacle Accuracy (college-optometrists.org). 2024.