Both eyes or one? The first clue
Start with the pattern, because it narrows the cause faster than anything else. Both eyes swollen and sealing shut together usually mean something systemic — the whole body is short of something, or an infection is working through the whole animal. One puffy eye, especially with the other bright and normal, points to a local problem: a scratch from a sharp stem or enclosure fitting, a particle of substrate trapped under the lid, or an injury from a cage-mate. Timing adds the second clue. A tortoise that wakes from brumation with mildly puffy eyes that clear within a day or two of warmth and soaking is showing a common, transient pattern; eyes that stay shut, worsen, or come with discharge and appetite loss are a different matter and should not be filed under 'just woke up'.
The vitamin A connection
The most common cause of both-eyes swelling is a diet short on vitamin A. Without enough of it, the glands in the eyelids and the surface of the eye change and swell until the lids press the eyes closed — and the deficiency builds over months on a narrow diet of low-nutrient greens and little variety. The fix is dietary breadth — dark leafy greens and orange vegetables in regular rotation — confirmed and guided by a vet, because the same vitamin in excess, particularly by injection or heavy supplementation given blindly, can damage a tortoise too. That balance is why 'just add a supplement' is not a safe home answer: a vet who knows the diet history can correct the deficiency at the right pace while checking that the eyes themselves have not been damaged by weeks of being sealed.
Air, dust and infection
Indoor enclosures create the third family of causes. Substrate that is very dry and dusty irritates tortoise eyes day after day, and low humidity compounds it until the lids swell in protest; a tortoise rubbing its eyes with its front legs is showing you irritation in real time. Respiratory infection runs alongside eye trouble often enough that the two should always be checked together: a swollen-eyed tortoise with a runny nose, bubbles at the nostrils, or audible breathing is likely dealing with one illness showing in two places. At home, the supportive steps are warm shallow soaks once or twice daily, substrate checked for dust and refreshed where needed, and a review of humidity — never prising the lids open, and never borrowing human eye products, neither of which helps and both of which can injure delicate tissue.
When the vet cannot wait
A tortoise navigates its world by sight and smell, and one that cannot open its eyes will not graze, so sealed eyes plus refused food is a combination that should be seen within days at the latest. Thick discharge, breathing noise, lethargy, or eyes swollen shut in a tortoise that has recently brumated all move the appointment sooner. Bring the working details with you: what the tortoise eats in a real week, what substrate it lives on, its soak routine and when the eyes first changed — the cause of this symptom lives in those answers more often than in the eye itself. Diet notes, soak routine and vet findings recorded in your tortoise's KinsLe Pet Passport let you hand over that history precisely instead of estimating it in the waiting room.