For people with celiac disease hidden gluten in their diets is the main cause of elevated Tissue Transglutaminase IgA Antibodies (tTG-IgA), but there are other conditions, including cow's milk/casein intolerance, that can also cause this, and here is an article about the other possible causes:    

Eye irritation can be so frustrating, especially when you're already adjusting to life with celiac disease. It’s great that you’ve seen an eye doctor and taken steps like using a heat mask and drops, which seem to have helped with the dryness. Sometimes, lingering irritation can be linked to inflammation as your body heals, or even to other factors like allergies or environmental irritants (like dust or mold that might increase in colder months). Do you use lubricant eye drops like "Refresh"? I use this often, because I also have dry eye issues at times. It might also be worth reviewing your diet and environment for hidden gluten or allergens, as cross-contamination could contribute to systemic inflammation and affect your eyes. Some celiacs report lingering or unusual symptoms during the first year of healing—it’s a process, but you’re on the right track. If it persists, consider a follow-up with your doctor or an allergist to rule out anything else. Hang in there—you’re doing everything right to support your recovery!

PS - This article has more info:  

Thanks for sharing this! One of our long time authors share this one a few years back, but I haven't tried it:  

Welcome to the forum! Keep in mind that if you quit eating gluten before all testing is done, you may have inaccurate, possibly false negative, test results.  When you stop eating gluten, your body stops making the antibodies which are measured in the blood tests.  Stopping gluten before an endoscopy may make the intestinal damage harder to detect, and a false negative biopsy may result.  As uncomfortable as it is, finish all testing before going gluten free.