Is there any discharge from the eye?
Is just one affected or both?
Does the nictitating membrane (the translucent inner eyelid) appear and cover part of the eye?
What is Dexter doing right before this happens?
Without seeing what is happening it's hard to say what is causing it. It's possible a loose hair or dust is getting in his eye, could be a cold virus etc.
Have you mentioned this to your vet?
Avoid biting when a simple growl will do
The Spirit Lives As Long As Someone Who Lives Remembers You - Navaho Saying
Vindication ~ For all those pets who became sick or lost their lives from tainted pet food