Allergan agreed to buy an interocular lens maker.

The pending purchase of American Medical Optics, the nation’s third-largest maker of plastic lens replacements for cataract patients, was seen as Allergan’s best way to enter the lens market and expand its line of eye-care products. Terms of the deal, expected to close next month, were not disclosed. Allergan, of Irvine, is a subsidiary of SmithKline Beckman; American Medical Optics is a unit of Baxter Travenol Laboratories.