What is the most likely cause of a gray ring observed on the edge of both irises in an 80-year-old woman with no visual changes?

The presence of a gray ring observed on the edge of both irises in an elderly individual is characteristic of arcus senilis. This condition is a common finding in older adults and is caused by the deposition of lipid material in the corneal stroma, resulting in a gray or white arc around the corneal margin. It typically does not affect vision and is often seen bilaterally.

In elderly patients, arcus senilis usually occurs without any underlying systemic diseases, and it is not indicative of hyperlipidemia in most cases, especially when occurring after the age of 50. The appearance of this ring often signifies normal aging changes rather than any acute pathological condition.

The other conditions listed do not typically present with this specific finding. Pinguecula refers to a yellowish, raised growth on the conjunctiva that usually does not form a ring around the iris. Peripheral cataracts can cause vision changes and are not typically represented as a ring on the iris. Macular degeneration affects central vision and does not present with a ring-like appearance around the iris. Hence, the correct identification of arcus senilis aligns well with the clinical presentation described.