Really, glasses get smudged from a number Gun Powder and Lead gun lover shirt of things; your fingers, sweat, humidity, bugs; basically everything that would hit a fully sighted person’s eyes. For that reason I don’t mind having to occasionally clean my lenses; I’m not getting pelted by bugs, tree branches, and my own fingers. If it is a camera lens, then you might read up on how to properly clean the lens before you harm it. Knowing perhaps what is the cause of the smudge would help. There are specialized cleaning solutions and brushes and specialized lens paper for cleaning. But please do not use any commercial solutions or any thing that is not specifically recommended for camera lenses, you will just ruin the lens.
This response has been edited to add critical information. Gun Powder and Lead gun lover shirt See below. You can guard your drawings against smudges by using either a chemical or physical barrier. For the chemical route, it is important to know what fixative is and what it does. Fixative is a varnish that coats and affixes the pigment to the substrate (i.e. paper). The fixative typically comes in an aerosol can but can be found in a pump spray bottle. Fixatives are also available with special formulations for the medium. The specializations are crafted for pencil, pastel, charcoal, colored pencil, etc. Fixative is available with different levels of sheen –matte, semi-gloss, and gloss.