Lens regeneration in newts, called Wolffian regeneration, proceeds from pigmented epithelial cells at the dorsal margin of the iris. Those cells lose pigment, re-enter the cell cycle, and rebuild a transparent lens over several weeks, without drawing on a reserved stem-cell pool.
A study published in 2011 tested whether that capacity degrades with age and repetition. Newts had their lenses removed eighteen times over sixteen years, and the regenerated lenses were examined for structure and gene expression. They matched lenses from control animals of similar age; the ability had not measurably declined, and the animals were themselves old by then.
The result is often overstated into claims about ageless newts or about immediate human application. What it shows is that a specific regenerative pathway in one species does not exhaust itself with repeated use or advancing age. Whether the same is true for other tissues, or in other species, is a separate question.