The short version
14 companies supply this market — deep enough that no single failure threatens the supply. The generic price has fallen 35% in a year, to $10.70 per mL — and generics that get this cheap tend to get abandoned rather than defended. The brand (Alphagan P) runs $37.33 per mL — 3.7× more. Put together: this looks like a healthy supply — the boring kind, which is exactly what you want.
The numbers behind every sentence are on this page below — and the Watch button emails you when any of them move.