A hitch assembly for connecting a front end 21 of a low-loader trailer to a tow vehicle 10 is disclosed. A first portion of the gasket is shaped to fit within a groove or recess of the corrugated pipe. In addition, methods of filling a cavity of a lens with transparent fluid, methods of adjusting the pressure of fluid in the cavity, and methods of sealing such a cavity are described, as well the use of such lenses in adjustable spectacles.