Today is my birthday. One of the good things that happened is that my TJack faceshell+lenses combo arrived! Talk about a sweet gift. To celebrate, here's a tutorial on how to cut the eye holes for your masks.
How to cut the eye holes:
You may need a stand-in head to mount your mask and faceshell. I bought this one in particular:
Amazon.com: Case Pack of 1 Giell Styrofoam Foam Mannequin Wig Head Display Male White: Beauty
Step 1: Mount your mask on the styrofoam head
WITH THE FACESHELL (really important if you want to get the eye measurements right). Make sure that the center webbing of the mask is at the center of the head, just right above the nose bridge.
Take your time aligning the mask. It's really important that it's aligned correctly.
Step 2: Measure the distance between your eyes. Take that distance and divide it by two. That number will then be the center of your mask (Thanks, Lunaman, for this info). For example, my distance was 8cm. Which means 4 is my center. Refer to the picture:
Step 3: Using a fabric marker, make little circles to mark where you're going to cut your mask. Use the measurement you took above to gauge the distance from the center of the mask for each eye. Make small ones first. You can always adjust the size later when you get it right (Thanks again, Lunaman, for the info). I used an orange marker.
Step 4: Remove the mask from the stand-in head. Flip it inside out. Depending on what marker you used, you will see some sort of a mark. Use that as your reference point for cutting the eye holes.
Again, cut small holes first!
Step 5: Flip the mask over again and you're done! This is what the eye holes look like.

The fabric will not unravel if you used 4-way stretch Lycra. If you want, you can reinforce the holes by stitching them or putting glue to be sure they don't grow any bigger.
Now if you'll excuse me, I will be celebrating my birthday as Spider-man!
Thanks for reading