Swelling and formation of hard, tender nodules years after tear trough filler treatment can be due to a few reasons. One possibility is that it could be a delayed hypersensitivity reaction to the filler material. Another possibility is that these nodules could be granulomas, which are inflammatory reactions that can occur in response to foreign material in the body. It's important to note that these symptoms should not be ignored, especially if they are recurrent. It's recommended to consult with the physician or dermatologist who performed the procedure or another qualified healthcare provider. They can evaluate the area, possibly using ultrasound or another imaging technique, and determine the best course of action. This may include treatments such as corticosteroid injections, hyaluronidase injections if the filler was hyaluronic acid-based, or in some cases, surgical removal of the nodules. Remember, it's crucial not to try and self-diagnose or self-treat these issues. Always seek professional medical advice.