What can I do to fix my negative canthal tilt? (Photo)

It will likely require lower eyelid retraction surgery with canthoplasty and possibly upper eyelid ptosis surgery to have effective, safe, long lasting results. Canthoplasty by itself will not work. These are very specialized procedures. Seek an expert.

Great question and thank you for providing a great photo.
I think you hit the nail on the head with your diagnosis. However, the treatment of choice is not always completely black and white. I believe you would likely require some sort of canthoplasty (addressing the lateral corner of the eyelids where they meet), but may also require additionally procedures like upper blepharoplasty and/or brow lift to improve symmetry and ensure best possible outcomes.  
Hope this helps and best of luck!Kyle Kimura, MD

An upper eyelid procedure along with the lateral tightening of the lower lids can possibly help improve your issues. It is best to consult a board certified facial plastic surgeon in person and discuss your goals and options after a physical examination.Hope this helps,Ali Rıza Öreroğlu, MD FEBOPRASEuropean and Turkish Board Certified Aesthetic, Plastic and Reconstructive SurgeonIstanbul, Turkey

As you have correctly noted you have a negative canthal tilt to your eyes and they are asymmetrical. The exact nature of the problem is difficult to determine without an examination. However, from your photo alone, you appear to have an orbital asymmetry with the orbit on the right side of the photo being displaced inferiorly. While a canthopexy would improve the downward tilt of each of the lower lids, it would not create greater symmetry. The most effective, permanent correction for a bony abnormality would be surgical repositioning of the orbits. More conservative treatments may be available to camouflage the problem. Consult an occuloplastic surgeon for a thorough evaluation.

The ptosis can be repaired and the lateral canthal angles reset. This will make the eyes more almond shaped. A detailed personal assessment is the next step when you are ready. Recognize that not all surgeons are the same. You need an aesthetically oriented eyelid surgeon.