I'm Asian, and our faces are (obviously) somewhat differently shaped than the standard mould that has been used by most eyeglass manufacturers. Recently, some makers like Oakley have started making select styles in an "Asian Fit" that modifies the frames and lenses to better fit our faces. Sadly, not all styles are available.
In this project, I took a pair of Oakley Half X glasses and cut the lenses so that they no longer touched my cheekbones.
Yes, these are $300+ sunglasses and I took a belt sander to them.
Step 1: See Where They Glasses Are Hitting.
The only suitable frames for this project are ones in which there is an exposed lens edge to modify. (in other words semi-rimless frames.
Put the frames on and note where the lenses are touching your face. It's a judgement call as to whether it is feasable to remove enough material to make the lens fit, how much to remove, and whether the remaining shape will be aesthetically pleasing.
Step 2: Mask the Lenses
You need to find a tape that will stick to the lenses, but not so much that it will remove any coatings. I used 3M blue painters tape, but found that it did not stick very well to the Oakley treated lenses and did not have quite enough stretch to conform to the wrap lens.
On the other hand, it worked well enough.
Your main goal in masking the lens is to delineate exactly how much lens you will be grinding off. Put the tape on the part of the lens you will be KEEPING and leave the part you will be grinding unmasked. This way you can measure/eyeball the masking on both sides to make sure that you have masked symmetrically.
In this case, I'm removing just enough material to eliminate the "Polarized" etching on the corner of the lens, then blending the corners back in to match.
Step 3: Grind
Next, Grind off the excess lens material. Polycarbonate tends to melt and form a burr if you go too fast, so take it slow.
You can either freehand it using a dremel-type tool and an abrasive drum (the kind that comes in almost every dremel kit), or do what I did and take it to a beltsander with a relatively fine grit belt. I chose the belt sander to ensure that the bottom edge had a nice straight line to it.
Step 4: Keep Grinding
This may take a while. Every so often, check to make sure that you haven't gone past the tape. If you have, you're going to need to re-evaluate you final lens shape, or buy new lenses, so go slowly.
If you build up a burr because you went too quickly, lightly grind on a slight angle towards the burr to cut it off, then continue. Alternately, you can stop grinding and roll the burr back over the edge with your fingernail if it isn't too thick yet.
Step 5: Test Fit
Once you have both sides done symmetrically, you can take off the tape and try them on. Don't do this after having done only one side. Remember, you're using the tape as your guideline to make sure that both lenses are the same shape. If you remove the tape before you've done both sides, you're going to be back to eyeballing it.
If you find that you need to remove more material, go back to the beginning and re-mask the lenses.
Step 6: Finish the Edges
I finished the edges of the glasses freehand, initially with the dremel to finalize the shape of the lenses at the corners, and then to round the edges of the lens to match the original profile. Use a low speed and get it rounded slightly, then switch to a sanding stick.
During this step, I removed the masking tape. Yes, there was more risk to the lenses, but I found it easier to make sure I was removing the burr from the lens edge without the tape there. Surprisingly, I found that the dust from grinding the lens did not scratch the coating at all, which makes sense since the surface coating of the lenses is much harder than the actual lens itself.
In this picture, you can see how nicely the edge comes out. There is no damage to the mirror coating, and if you take your time, it will look like a factory edge.
Step 7: Finished Product
Here's the finished product. You can see from the inset image how much the profile has changed.
It was actually much much much easier than I expected. Practice on a pair of dime store glasses first until you get the hang of working with polycarbonate.