Onychauxis is a uniform thickness of the toenails without deformity. Onychauxis is mostly associated with older age and poor circulation as well as repeated trauma to the nails from the footwear or a single episode of trauma a like dropping a brick on the foot. Occasionally there might be a disease process that underlies the thickening of the toenails.
There is really no way to cure onychauxis. All that can be done is to keep the nail short, which can be difficult if the nail is thick. In those cases, a Podiatrist might need to be consulted to have the thickness of the nails on a regular basis.