The cleaning of camera window is a delicate process as the window material is quite soft. It is recommended NOT to use standard paper towels or workshop wipes, as these often contains abrasive materials. If the window of the camera is fouled with "normal dirt" from the sea, say salt, fish-blood, etc. it is probably just as good to use clean fresh water on a microfiber cloth.
Do not clean with any petroleum based chemicals (white spirit).