Patient compliance and the "usefulness product" of timolol.

The practical value of any therapy depends upon a combination of effectiveness of the agent (or procedure) and the extent to which the patient complies in its proper administration. Thus, it might be said that the multiple of effectiveness times compliance equals the "usefulness product." Among the various glaucoma therapies, this product seems to range from about 30%--90%. Timolol's effectiveness in lowering intraocular pressure combined with its low incidence of side effects yields a high usefulness product, and this may decrease the incidence of surgery required for the treatment of the open-angle glaucomas.