I've seen a lot of people very frustrated by the eye puzzle in LINC (when you're trying to get the tuning fork). I was, too, so I thought I'd document the process that helped me reliably solve it, as a lot of the other answers on here are somewhat less specific.

1. Turn of FX in the menu. I've noticed that the sound effect playing seems to keep my cursor from appearing for just a second longer than without the FX. This may be superstition, but it can't hurt!

2. After you've blinded the eye in the first room (the entry room), exit right and walk up to the second eye.

3. Turn your game speed ALL THE WAY DOWN. This will help!

4. Use blind on the eye, and then immediately HOVER your cursor over the North exit.

5. As soon as you get the exit cursor back click ONCE on the exit. Not twice. Not three times. Once. (This is what kept getting me zapped).

6. DO NOT TOUCH ANYTHING. If you've done it correctly you should be going through the portal just as the eye unblinds.

7. After this, it's pretty much cake. Ignore everything but getting to the tuning fork (there's only one set of unblocked doors, so it should be pretty clear). You should get there just in time to pick it up. Again DO NOT HESITATE. Click it ONCE as soon as possible. You should be able to pick it up just as the first eye unblinds.

Hope this helps folks who were having problems!