What does a keyhole bridge primarily do?

A keyhole bridge primarily serves to distribute weight effectively across the sides of the eyeglass frame. This design helps ensure that the frame rests securely on the wearer's nose without placing excessive pressure on any one area. By concentrating the weight on the sides, the bridge enhances comfort and stability for the wearer, especially for glasses that might otherwise slide down the nose.

A keyhole bridge is characterized by its unique shape, which typically includes a cut-out area that allows a more customized fit for various nose shapes and sizes. This design can accommodate a range of distances from the bridge of the nose to the ears, ensuring that the frame sits properly during wear.

In contrast, other designs that focus on weight distribution across the top or the entire frame may not provide the same level of comfort or stability, which is why the keyhole's specific distribution method is so important in ophthalmic dispensing.