As used in this part:

Ophthalmic drug product. A drug product, which should be sterile in accordance with § 200.50, to be applied to the eyelid or instilled in the eye.

Astringent. A locally acting pharmacologic agent which, by precipitating protein, helps to clear mucus from the outer surface of the eye.

Buffering agent. A substance which stabilizes the pH of solutions against changes produced by introduction of acids or bases from such sources as drugs, body fluids, tears, etc.

Demulcent. An agent, usually a water-soluble polymer, which is applied topically to the eye to protect and lubricate mucous membrane surfaces and relieve dryness and irritation.

Emollient. An agent, usually a fat or oil, which is applied locally to eyelids to protect or soften tissues and to prevent drying and cracking.

Eyewash, eye lotion, irrigating solution. A sterile aqueous solution intended for washing, bathing, or flushing the eye.

Hypertonicity agent. An agent which exerts an osmotic gradient greater than that present in body tissues and fluids, so that water is drawn from the body tissues and fluids across semipermeable membranes. Applied topically to the eye, a hypertonicity agent creates an osmotic gradient which draws water out of the cornea.

Isotonicity. A state or quality in which the osmotic pressure in two fluids is equal.

Vasoconstrictor. A pharmacologic agent which, when applied topically to the mucous membranes of the eye, causes transient constriction of conjunctival blood vessels.