I have strange issue.
Look at the picture.
My avatar has eyes, but when them behind glasses, they become invisible, How to solve this?

I encountered a similar problem in the past.  Part of my character's clothing would dissappear when I looked through an automobile window at the character who was seated inside.  I don't know of a "guaranteed to work" fix, and in my case it was minor so I simply accepted it.

Here is a crazy idea...  Change the Opacity on the eyes to "99" and see if that makes it behave.

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iClone 7... Character Creator... Substance Designer/Painter... Blender... Audacity...
Desktop (homebuilt) - Windows 10, Ryzen 9 3900x CPU, GTX 1080 GPU (8GB), 32GB RAM, Asus X570 Pro motherboard, 2TB SSD, terabytes of disk space, dual  monitors.
Laptop - Windows 10, MSI GS63VR STEALTH-252, 16GB RAM, GTX 1060 (6GB), 256GB SSD and 1TB HDD