What device is essential for holding a block on a lens securely?

The blocker is an essential device used in the lens fabrication process for securely holding a block on a lens. A block is a piece that is attached to a lens so it can be manipulated during various stages of manufacturing, such as edging. The blocker ensures that the lens is firmly secured, minimizing movement and ensuring precision when shaping or fitting the lens into frames. This level of stability is crucial for achieving accurate prescription lenses, as even slight movements can lead to misfits or errors in the final product.

Understanding the role of the blocker highlights its significance in the overall process and maintains the quality and accuracy desired in the optical industry. Other devices listed, such as the carrier, caliper, and optometer, serve different purposes in optometry and dispensing but do not function specifically to secure a block to a lens. For instance, a carrier may transport lenses, a caliper measures thickness or dimensions, and an optometer is used for measuring visual acuity or refractive errors. Each plays its part but does not fulfill the specific need for securely holding a block on a lens, demonstrating the unique role of the blocker in lens processing.