An apparatus for measuring pressure of fluid in a shunt includes a distensible member arranged adjacent to a graduated scale. The shunt includes a shunt valve and the apparatus is attachable to, or incorporated into the shunt at a location either at the shunt valve or upstream of the shunt valve. Both the distensible member and the scale include radiopaque markers. The fluid in the shunt acts directly on the distensible member and the distensible member is distensible in the direction of the scale.

A method for assembling a syringe includes supporting a syringe barrel having a stopper being movably disposed therein. A distal end of a plunger rod is inserted into the compartment of the syringe barrel. An initial digital image is taken of the stopper within the syringe barrel. The distal end of the plunger rod is coupled to the stopper located within the syringe barrel so that the plunger rod is secured to the stopper. A plurality of further digital images of the stopper within the syringe barrel are taken during or after coupling the distal end of the plunger rod to the stopper. Information determined from each of the further digital images is compared to information determined from the initial digital image using a computer processor to determine if the stopper in each of the further digital images has moved relative to the syringe barrel.

A pressure differential indicator that eliminates the risk of providing a false positive due to fluid contamination. The invention has an electrically insulated barrier between the hot pin and the grounded housing without the need for a hermetic seal. The indicator can be manufactured at a greater efficiency and lower cost than is found with prior art pressure differential indicators. It has a piston that can be easily oriented to yield either a normally closed or normally open position. The indicator has at least one protrusion on a plastic overmold to engage the swage collar and resist axial rotation of the pin. A pressure seal interrupting the plastic overmold sections and exposing the underlying metal to allow for an O-ring seal with no potential leak path between plastic and metal. Finally, the pressure differential indicator has all moving components contained within a single cavity.

A method of detecting presence or absence of a magnetic measurement probe at a measurement launch position in an electromagnetic coil of an ophthalmic instrument includes applying a temporary current pulse to the electromagnetic coil, detecting a counter-electromotive force voltage spike induced in the electromagnetic coil by the current pulse, evaluating a decay behavior of the counter-electromotive force voltage spike, and correlating the decay behavior of the counter-electromotive force voltage spike to presence or absence of the measurement probe at the measurement launch position.