In a well-made prosthetic eye, tears should flow evenly across the prosthesis just as they do over the natural eye — in a sheet-like fashion, rather than collecting in droplets. We call this type of behavior hydrophilic — “water loving.” Hydrophobic (“water fearing”) artificial eyes repel water, much like the surface of a waxed car.

The difference between a hydrophilic and a hydrophobic piece can have dramatic differences in the satisfaction for the patient. Hydr...