If you have got to my age (or had other bad luck) you no doubt need glasses. I now wear progressive frameless titanium glasses (14 grams) all the time, but I also need a spare pair in case I lose or break them. The quite lightweight case they came in from Zenni weighs 47 grams (blue below). I knew I could do better. Like this:
As you can see I have also managed to fit in a pair of clip on sunglasses, Weight 4.5 grams eg to prevent snow blindness!
This is 350 ml (12 oz) PET drink bottle I cut down with a craft knife (I should have left a tiny bit more of the neck) and some bubble wrap = 12 grams, a saving over over an ounce ie more than the weight of a muesli bar on the trail, or more than enough weight of fuel (metho) to cook a meal. Every little bit of weight saved helps lighten the load and means you can go a little bit further, easier. I could have even cut down on the (used) bubble wrap a little more.
Here it is compared with my old glasses case.
PS: I found this empty container makes an excellent ultralight glasses case.http://www.theultralighthiker.com/hormel-real-bacon-pieces/
Indeed switching to these frameless glasses (two pairs) also saved me over an ounce (28.5 grams)! I have simply rolled the glasses up in the bubble wrap and squeezed them through the neck. These flexible titanium frames are quite difficult to break anyway: you can just about stand on them, so they will be fine in the ‘possibles’ bag in my pack.
This ultralight glasses case has been safely stowed (without any due care) in my pack now for over a year and maybe a thousand miles. All its contents came out perfectly for a photo this morning. If you are a bit wary of trusting your spare glasses to such a flimsy container, you might use an empty Hormel Bacon container (which weighs 33 grams) or one of these carbon fibre cigar cases at 28 grams.