Study of Serine Supplementation to Protect Vision in MacTel

The goal of this clinical trial is to look at the efficacy and safety of giving oral serine (an amino acid) on the progression of structural and functional changes of the retina in people with MacTel type 2. The main questions it aims to answer are: * Does serine slow the progression of MacTel? * Is long-term serine supplementation safe in people with MacTel? Researchers will compare serine to a placebo (a look-alike substance that contains no drug) to see if serine works to slow the progression of MacTel. Participants will: * Take serine or a placebo twice a day for 24 months * Visit the clinic once every 6 months for eye exam, eye imaging and blood tests * Keep a diary of their symptoms, missed doses, and changes in medications