<prompt> Tonography is used to determineThe lOP at different timesThe facility of aqueous outflowThe rate of formation of aqueousNone of the above  <response>: Tonography Tonography is a non-invasive technique for determining the facility of aqueous outflow C-value. The C-value is expressed as aqueous outflow in microlitres per minute per millimetre of mercury. It is estimated by placing Schiotz tonometer on the eye for 4 minutes. For a graphic record the electronic Schiotz tonometer is used. C-value is calculated from special tonographic tables taking into consideration the initial IOP P0 and the change in scale reading over the 4 minutes. Ref:- A K KHURANA; pg num:-481 