If it's not on the surface but is in the eye, as that's what it appears to be in the photo, it's likely uveitis caused by the parasite e. cuniculi. This parasite gets into the eye due to it being passed to a kit while developing in the doe prior to birth. A scratched cornea may also be a possibility.
Encephalitozoon cuniculi is a small pathogen that is spread in urine and mainly affects the nervous system (brain and spinal cord) and kidneys. The disease is very common in the pet rabbit population and can be carried by other animals including wild rabbits.
You would need to consult with an experienced rabbit vet to determine what treatment is needed, immediately if it's painful and causing a lack of appetite, as your rabbit will need to be put on eye meds, pain/anti inflammatory meds, and will need assisted syringe feeds (to prevent GI stasis). Your rabbit will also likely need to receive the month long oral fenbendazole treatment for e cuniculi, which your vet should prescribe, or will need antibiotic eye drops if it's a scratched cornea.