I would advise you to stop keep the dragon on sand. Use newspaper. Most likely the fine sediment/silt from the sand is causing the issue.
Is the dragon well hydrated? Offer water and gets occasional warm baths? Scrub the eye area lightly with a soft bristle tooth brush.
It might have an eye infection and require solution from a vet or try an eye flush solution over-counter if money is an issue.
good luck
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