▁hum our ▁in ▁the ▁posterior ▁segment ▁has ▁a ▁relatively ▁fixed ▁volume ▁and ▁thus ▁does ▁not ▁affect ▁int ra oc ular ▁pressure ▁reg ulation . ▁ ▁An ▁important ▁quant itative ▁relationship ▁( G old mann ' s ▁equation ) ▁is ▁as ▁follows : ▁ ▁Where : ▁▁ ▁is ▁the ▁I OP ▁in ▁mill im eters ▁of ▁mer cur y ▁( mm H g ) ▁▁ ▁the ▁rate ▁of ▁a que ous ▁hum our ▁formation ▁in ▁mic rol it ers ▁per ▁minute ▁( μ L / min ) ▁▁ ▁the ▁res or ption ▁of ▁a que ous ▁hum our ▁through ▁the ▁u ve os cler al ▁route ▁( μ L / min ) ▁▁ ▁is ▁the ▁facility ▁of ▁out flow ▁in ▁mic rol it ers ▁per ▁minute ▁per ▁millimeter ▁of ▁mer cur y ▁( μ L / min / mm H g ) ▁▁ ▁the ▁epis cler al ▁ven ous ▁pressure ▁in ▁mill im eters ▁of ▁mer cur y ▁( mm H g ). ▁ ▁The ▁above ▁factors ▁are ▁those ▁that ▁drive ▁I OP . ▁ ▁Me asure ment ▁ ▁In tra oc ular ▁pressure ▁is ▁measured ▁with ▁a ▁t onom eter ▁as ▁part ▁of ▁a ▁compreh ensive ▁eye ▁exam ination . ▁ ▁Me as ured ▁values ▁of ▁int ra oc ular ▁pressure ▁are ▁influenced ▁by ▁cor ne al ▁thick ness ▁and ▁rig id ity . ▁As ▁a ▁result , ▁some ▁forms ▁of ▁ref ract ive ▁surg ery ▁( such ▁as ▁phot ore f ract ive ▁ker ate ct omy ) ▁can ▁cause ▁traditional ▁int