An optical mouse's "optical surface sensor" must be kept a certain distance from the table for it to function properly.
A new optical mouse's plastic base is designed to keep the "optical sensor" an optimum distance from the table.
After many hours of moving the mouse about on a table, the mouse's plastic base slowly wears away causing the optical sensor to become to close to the table's surface which then causes the sensor to malfunction (jittery, slow unresponsiveness).
The simplest way to correct this problem is to is to rebuild the base's surface. This is done by sticking on a few layers of sticky labels onto the bottom of the mouse so as to raise the optical sensor up from the table to the distance it was when the mouse was new.
As time goes by and when the labels eventually wear out from use you can just replace them.