Abstract: A pneumatic pressure probe for use in measuring pulsatile ocular blood flow comprises a housing consisting of an air tight bearing defining a pressure chamber, a piston having an axial bore communicating with the pressure chamber, the proximal end of the piston carrying a counter balancing weight and being received in the pressure chamber and the distal end of the piston extending outwardly of the housing and carrying a disposable sensing head. A transparent membrane is integrally attached to the sensing head and is substantially perpendicular to the piston axial bore and an interior channel through which light is emitted to the membrane from an LED mounted in the housing. The probe allows the patients visual axis to be aligned with the axial bore of the piston by focusing on the light source during measurement enabling the applanated comae and sensing membrane to be maintained substantially parallel and substantially perpendicular with the axial bore of the piston.