Non-contact tonometer having improved air pump

#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 system 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 is arranged in flow communication with the plenum chamber.

#A common fluid pump system found in non-contact tonometers includes a rotary solenoid having a driven armature, a piston rod pivotally coupled to the solenoid armature, a piston fixed to the end of the piston rod for travel therewith, and a cylinder receiving the piston in close slidable fit to allow axial movement of the piston relative to the cylinder during a compression stroke. An example of this type of fluid pump system can be seen in U.S. Pat. No. 3,585,849 issued Jun. 22, 1971. In fluid pump systems of the type described, the driven armature, piston rod, and piston are connected in series, and thus the radial position of the piston in the cylinder is influenced by the driven armature and piston rod. Consequently, the solenoid, piston rod, piston and cylinder must be manufactured and located according to close tolerances to ensure that the piston moves in axial alignment with the cylinder during a compression stroke.

#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. NCT 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.

#As a prerequisite to testing, it is necessary for an operator 8 to align NCT 10 in three dimensions (X-Y-Z alignment) relative to the patient's eye. The patient is instructed to gaze at a target image presented along optical axis OA by a target light source 23 and a beam splitter 29. The operator 8 is preferably guided in coarse alignment of NCT 10 by viewing the patient's eye through operator eyepiece 16 along an optical axis OA that coincides with test axis TA. A planar-planar objective lens 19 on optical axis OA cooperates with front window 18 to support fluid discharge tube 24 without blocking the operator's view of the patient's eye. In a preferred embodiment, an opto-electronic position detection system 40 associated with nosepiece 25 senses the position of an outlet orifice 42 of fluid discharge tube 24 relative to a corneal vertex V and provides signal information used to drive an instructive “heads up” display 44 providing real time X, Y, and Z alignment cues. An image of instructive display 44 is projected to the operator along optical axis OA by a beam splitter 46, such that the instructive display image is optically superimposed with an image of the patient's eye as viewed by the operator. Proper alignment is confirmed by position detection system 40. Reference numerals 48 and 50 respectively denote an emitter and a detector of position detection system 40. Commonly owned U.S. patent application Ser. No. 09/992,875, filed Nov. 6, 2001 and incorporated herein by reference in its entirety, describes a preferred alignment system in greater detail at paragraphs [0022] through [0036] and FIGS. 3-10.