The lens inside your eye holds the highest protein concentration of any tissue in the body, and no blood supply at all. Over decades those crystallin proteins oxidise, unfold and clump together. The clumps scatter light. That is a cataract, and the only fix is taking the lens out. Modern removal is phacoemulsification, and it is a genuinely strange piece of engineering: - A 2.2 mm incision is cut into clear cornea in two planes, so internal pressure presses the flap shut against itself. No sutures. - The anterior capsule, a basement membrane around 14 microns thick, is torn in a continuous circular curve roughly 5 mm across. Torn, not cut. A controlled tear follows the collagen and resists propagating under stress. - Fluid is injected beneath that opening to float the lens free of its shell. - A titanium needle oscillating at 28 to 45 kHz enters. Stroke length is only 50 to 100 microns, but at those frequencies the tip destroys lens material through direct impact and through cavitati...