> Despite the often longer life-expectancies, nuclear pacemakers quickly became a part of the past when lithium batteries were developed. Not only did the technology improve, allowing for lighter, smaller, and programmable pacemakers, but doctors began to realize that this excessive longevity of nuclear pacemakers was excessive.
"The History of Nuclear Powered Pacemakers" - http://large.stanford.edu/courses/2015/ph241/degraw2/
> Despite the often longer life-expectancies, nuclear pacemakers quickly became a part of the past when lithium batteries were developed. Not only did the technology improve, allowing for lighter, smaller, and programmable pacemakers, but doctors began to realize that this excessive longevity of nuclear pacemakers was excessive.
https://en.wikipedia.org/wiki/Betavoltaic_device says betavoltaic "devices include a 100 μW tritium-powered device weighing 20 grams".
That's about 5x the weight of a glass eye - https://www.muellersoehne.com/907.html .
Assuming linear scaling, an energy budget of 2μW isn't going to provide much light.