It is generally accepted that the intraocular pressure is determined directly by the rate of formation of aqueous humor, the resistance to outflow, and the recipient venous back pressure. The relationship during steady state conditions has been expressed in the following equation: Equation 1 (Fis the rate of flow of aqueous humor in the steady state,Pois the intraocular pressure,Pvis the recipient venous back pressure, andRis the resistance to outflow.) A sustained alteration of the intraocular pressure may result from a sustained change in the rate of formation of aqueous humor, in the resistance to outflow, or in the recipient venous back pressure. To study physiological and pharmacological effects upon the intraocular pressure ideally requires a technique of manometry which avoids irritation of the eye (and attendant breakdown of the blood aqueous barrier) and permits measurement of the intraocular pressure not only