I'm afraid your USB microscope will not do the trick. You need high magnification with a large depth of field and special lighting to see the wear. This is an expensive device, over $1000. The best way to do this is to take a picture of the stylus when new then a new one every year until you spot wear then replace it. The "cats eyes" refers to wear on spherical and elliptical styluses. With modern stylus profiles you will see squinting cat's eyes, more slit like. This is looking straight down on stylus. Traditionally I used a medical microscope with special lighting. The problem is a very low depth of field so you have to look at each view like you would a CT scan, one slice at a time.
Testing stylus wear.
I have an Ortofon 2M Blue stylus that I’ve had for 3.5 years. They advise up to 1000 hours of useful life but that’s just a rough estimate. I have not kept track of my hours of play. I’ll go for 3 weeks with lots of use and then a few more weeks of very little analog use and mostly digital use with my DAC. I just bought a lot of mint vinyl LP’s and got scared that my stylus may be worn, even though it sounds fine to me.
So, I have a new stylus and usb microscope on order. I just found an interesting article (http://www.pspatialaudio.com/stylus_wear.htm) that suggests something other than a visual inspection, since the tip is the only part of the stylus that gets worn and it’s apparently too small to judge even with a microscope.
The new method is to make two identical digital recordings--one with the older stylus and a second one with a new stylus. Then you A-B the two recordings. Since I already have a new 2M Blue coming tomorrow and another one on my turntable with unknown wear, I think I’ll give this method a try.
Has anyone heard of this? Any better ways to test if i should junk the old 2M Blue or somehow test it?