I actually thought optical microscopy worked just fine at this scale.

I know it’s not the case for this photo, but if a 7 μm red bloodcell is reflecting red light (700nm, aka 0.7μm) under a bright white light, wouldn’t the smallest discernable detail of the red blood cells be about a 10th of its width? Is that not roughly the detail we have in this image?

I’m making an assumption that the distance between discernable parts roughly parallels the wavelength’s width. I could be wrong tho