Non-contact tonometer

#The present invention relates generally to ophthalmic instruments, and more particularly to non-contact tonometers that measure intraocular pressure (IOP) by directing a fluid pulse at an eye to transfigure the cornea.

#Non-contact tonometers are well-known in the field of ophthalmology for measuring intraocular pressure (IOP) by directing a fluid pulse at the cornea to cause observable deformation of the cornea. Most commonly, the observable deformation is a flattening of a predetermined area of the cornea, a condition known as applanation. In prior art non-contact tonometers, the fluid pulse is generated by a fluid pump mechanism defining a plenum chamber for pressurized fluid. In order to direct the fluid pulse at the patient's cornea, a narrow cylindrical fluid discharge tube (also commonly referred to in the art as a “nozzle”) has an inlet orifice in flow communication with the plenum chamber and an outlet orifice that is aligned relative to the eye during testing.

#Since the early 1960s, when non-contact tonometers underwent initial development, through the present day, in which non-contact tonometers are very widely used by ophthalmic practitioners as a fundamental diagnostic tool, the shape of the fluid discharge tube has remained the same. Specifically, a length of narrow cylindrical tubing having flat ends and an axial flow passageway has been used faithfully as a de facto standard in non-contact tonometers to direct a fluid pulse from the plenum chamber to the eye. For example, U.S. Pat. No. 3,585,849 issued Jun. 22, 1971 gives an illustration of this universally adopted style of discharge tube at FIGS. 1 and 2, and further examples of this basic configuration can be readily found throughout the patent literature. While this type of discharge tube is inexpensive to manufacture and delivers a well-directed fluid pulse, it is not optimal from the standpoint of efficient fluid dynamics because of “vena cava” inlet losses and accompanying flow instability.

#The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which:

#FIG. 1 is a perspective view of a non-contact tonometer formed in accordance with a preferred embodiment of the present invention;

#FIG. 2 is a schematic diagram of the non-contact tonometer shown in FIG. 1;

#FIG. 1 of the drawings shows a non-contact tonometer (NCT) 10 embodying the present invention. NCT 10 is depicted as being a handheld instrument having a handle portion 12 and a head portion 14 at the top of the handle portion. While the present invention is described in the context of a handheld NCT, it can also be embodied in a table-top NCT. Handle portion 12 houses a rechargeable power source for energizing alignment and tonometric measurement systems carried by head portion 14. Also visible in FIG. 1 is an operator eyepiece 16 at one end of head portion 14, a front window 18 at an opposite end of head portion 14 for facing a patient, and a liquid crystal display 20 with pushbutton control overlay 22 angled toward the operator near operator eyepiece 16.

#FIG. 2 provides a schematic representation of the alignment and tonometric measurement systems housed by head portion 14. Non-contact tonometer 10 is operable to discharge a fluid pulse through a fluid discharge tube 24 aligned along a test axis TA to cause observable deformation of a patient's cornea C for purposes of measuring intraocular pressure. The fluid pulse is generated by a fluid pump system 26 communicating with fluid discharge tube 24, which extends through a nosepiece 25 fixed to a mounting member 27 seen in FIG. 3. A currently preferred fluid pump system is shown in FIG. 3 and comprises a linear solenoid 28 having a plunger 30, a piston 32 driven by plunger 30 and slidably received by a corresponding cylinder 34 to compress air within a compression chamber 35 when solenoid 28 is energized, and a plenum chamber 36 in flow communication with compression chamber 35 by way of a fluid conduit 38. Fluid discharge tube 24 extends into and communicates with plenum chamber 36.

#Of course, those familiar with the art of non-contact tonometers will realize that other fluid pump systems are also possible. By way of example, a pump system comprising a rotary solenoid connected to a piston by a pivotal linkage may be employed to compress fluid within a plenum chamber of the pump system with which the fluid discharge tube communicates. Other systems are also possible, including systems wherein a piston is driven by force supplied by a mechanical spring. It will be understood that the term “fluid pump” is not limited to the preferred fluid pump system described herein, and includes any system that functions to compress fluid.