https://phys.org/news/2018-05-team-optical-microscope-atomic-accuracy.html

Now, research developments at the National Institute of Standards and Technology (NIST) enable the microscopes to measure these nanometer-scale details with a new level of accuracy.

"We put the optical microscope under a microscope to achieve accuracy near the atomic scale," said NIST's Samuel Stavis, who served as the project leader for these efforts.