Patent Application
20050143637
The invention relates to the measurement of intraocular pressure and, in particular, to methods and apparatus for measuring intraocular pressure using applanation tonometry.
The measurement of intraocular pressure (IOP) is essential to the diagnosis and management of glaucoma, a major cause of blindness in the United States and around the world. Although direct measurement of intraocular pressure can be obtained by inserting a pressure sensitive probe into the eye, clinical methods must rely on indirect methods of obtaining intraocular pressure. There are two popular methods for obtaining these indirect measurements. In a first method, the eye is indented using a tonometer, popularized by Schiotz, wherein gram weights are placed on a central post that exerts pressure on a globe relative to a curved plate that covers an anesthetized cornea. This method has several disadvantages, which include the requirement that the patient remain in a supine position in addition to errors in measurement related to scleral rigidity. Also, the Schiotz tonometer requires a normogram to interpret the measured pressure.
The second method for obtaining an indirect measurement of intraocular pressure is the applanation technique, wherein a portion of the cornea is flattened by a mechanical device. In applanation techniques, the force required to produce a flattening of the cornea is related to intraocular pressure, so the intraocular pressure can be determined indirectly by measuring the flattening of the cornea and the pressure required to produce that flattening. Goldmann determined the exact area required such that one gram of force is equivalent to one mm Hg of intraocular pressure. McKay and Marg developed an electronic tonometer based on differential applanation between a central post and a surrounding annulus. This principle is utilized by the TONO-PEN™ electronic tonometer, patented by Feldon et al. in U.S. Pat. No. 4,747,296. A variant of the applanation methodology requires no direct contact with the patient's eye. This “air puff” technique involves directing a calibrated packet of pressurized air onto the corneal surface, which causes corneal flattening. This corneal flattening is then measured indirectly by measuring the deflection of light reflected from the corneal surface.
Of the various types of tonometers available for clinical use, the Goldmann applanation tonometer is considered the “gold standard.” However, there are several shortcomings to this technique. First, the device, as originally designed, is not portable, but is attached to a slit lamp. This issue has been addressed by the Perkins and Kowa tonometers that incorporate a Goldmann-type tonometer in a portable design. Second, these tonometers are manual devices that rely upon a highly trained observer to obtain reliable results. Third, the prolonged amount of time required to position the patient as well as poor patient tolerance make Goldmann tonometry inefficient and sometimes impossible to perform. Finally, a Goldmann tonometer touches the eye with a non-disposable device that is difficult to sterilize between uses. This increases the likelihood of transmitting infectious diseases or causing chemical damage to the cornea from residual antiseptic coming into contact with the patient's eye.
An applanation tonometer and method for measuring intraocular pressure are described herein, and particularly a new disposable tip for the tonometer. The invention allows for accurate measurement of intraocular pressure while addressing some of the deficiencies of existing tonometers.
An applanation tonometer for flattening the cornea of an eye is provided, wherein the applanator comprises a fiberoptics array; a force transducer for measuring forces applied by the applanator; an image transducer for obtaining data regarding an image of the applanated eye; and a processing circuit configured to calculate an intraocular pressure of the eye from at least a measured force and corresponding measured geometrical property. In aspects of the preferred embodiment, the geometrical property of the image may comprise an area, diameter, or major and minor axes of the cornea of the applanated eye. The tonometer may further comprise a light source for illuminating the eye, and a lens system adapted to focus an image of the applanated portion of the eye from the applanator to the image sensor. The tonometer calculates an intraocular pressure using a plurality of corresponding forces and geometrical properties of the applanation image as more particularly described in the above Ser. No. 10/137,234. As an important aspect of a preferred embodiment, the tonometer is provided with a new form of disposable tip that covers the applanator, thereby providing an improved replaceable, sterile interface between the tonometer's applanator and a patient's eye.
Thus more, particularly, the present invention is directed to a new form of disposable tip cover for use with an applanation tonometer and which comprises a light transmitting applanating region adapted to fit over the tip of a fiber optic applanator of the tonometer. The applanating region has a surface adapted to optically couple with an applanator and another surface adapted to contact the eye, and an attachment mechanism is provided for detachably attaching the tip cover to the tip of the fiber optics array. The disposable tip cover preferably comprises a thin optically diffusing translucent film, and the film preferably is sandwiched between an inner ring which is adapted to be disposed on the fiber optic array cylinder of the tonometer, and an outer ring for securing the film onto the inner ring for facilitating and providing intimate contact of a surface of the film with the outer surface of the cylinder.
The present application is directed to a new form of disposable tip, tip cover, and method of assembly for a handheld applanation tonometer. The above-identified application discloses the details of an applanation tonometer with which the present tip can be used, and also shows and describes a similar disposable tip which is retained on an elongated fiber optic array cylinder thereof which extends outward from the tonometer.
The ring assembly 17 comprises an inner ring 18 and outer ring 20 as illustrated in
The fiber optic array cylinder 12 provides a number of important optical and mechanical characteristics for the tonometer system. It is rigid and transfers the force of the applanation to a force sensor (not shown) within the tonometer 10 directly and without corruption. It provides collimation and therefore produces even and uninterrupted conduction of illumination to the interior surface of the tip cover 14. The optical properties of fiber optics naturally exclude ambient light which allows maintenance of even and optimized illumination for high image contrast while miminizing the effects of ambient illumination which may be present. It provides a sealed and long-protruding image conduit from the body of the tonometer 10 to allow the contact area thereof to be located some distance away from delicate interior components of the tonometer, and transfers the eye contact image through a solid interface into the interior of the instrument without distortion or loss of contrast. It provides a mechanically stable mounting surface for the disposable tip cover 14.
An active light source (not shown) within the tonometer does not illuminate the eye directly or require any fluorescent dyes, but rather illuminates the tip cover 14 distal surface. The tip cover 14 is translucent, and the tip cover provides certain unique optical characteristics. It suppresses the iris image and other image artifacts caused by reflection from structures located behind the cornea as a result of the diffusing properties of the film of the tip cover 14. The material preferably is an EMA film which is thin, preferably less than one mil, which is necessary to prevent distortion of the force signal. It is a neutral color, which helps to produce maximum image contrast. It is translucent which is necessary to allow light to be coupled out during contact with the cornea of the eye. It is diffusing to prevent spurious imaging of structures not in contact with the tonometer tip. It is impermeable to moisture which helps to maintain the tip 14 and fiber optics array 12 interface optical properties. It is non-wetting to prevent the collection of moisture and producing spurious images. It resists mechanical deformations of stretching, creasing or folding, to thereby prevent optical distortion of the contact image. It resists shearing or tearing to facilitate normal handling. It has low adhesion to allow convenient handling and avoid adhesion to the fiber optics array 12. It is biocompatible and non-allergenic and non-irritating which facilitates minimizing adverse reaction with a patient's cornea. It is low in cost to allow economic disposability, and disposable to prevent cross-contamination. It maintains its properties after sterilization, and allows radiation (gamma) sterilization to prevent infection. The present system with the tip cover 14 does not require the use of any imaging dyes as with other systems.
Preferably the tip cover film 14 is Ethyl Acrylate Copolymer film, preferably about 0.9 mil. in thickness. An example is Chevron Ethylene Methyl Acrylate Copolymer grade SP2255. The material is translucent and optically diffusing, thereby reducing depth of field of the imaging system while still passing a contact eye image. This material is very tough for its thickness and provides a barrier between the patient contact area and the tonometer tip 12. The tip cover 14 is meant to be low cost and disposable. It provides protection of the patient during patient to patient procedures.
Turning back to the drawings,
Turning again to
The inner ring 18 is attached to a mandrel 26. The mandrel is concentrically aligned with the cavities 64, 66 and 68 such that when lowered into the cavities, the inner ring 18 pushes the EMA film 14 over the outer diameter of the inner ring 18 as the inner ring is gradually pushed into the outer ring 20. The desired result is for the EMA film to be tightly secured between the two rings 18 and 20.
In this new 3-piece device the tip cover 17 must first be assembled with the film 14 as described above. After the tip cover is assembled to form the tip cover 16, it is placed into a cavity in a plastic clear copolyester compartmentalized tray 30 of
Thus, the film 14 is sandwiched between the outer ring 20 and inner ring 18 followed by application of the assembly onto the distal tip of the film cylinder 12.
Returning again to
While embodiments of the present invention have been shown and described, various modifications may be made without departing from the scope of the present invention, and all such modifications and equivalents are intended to be covered.
The present application is related to U.S. patent application Ser. No. 10/137,234 filed Apr. 30, 2002, the disclosure of which is fully incorporated herein by reference. The present application is a regular utility application claiming priority from U.S. provisional patent application Ser. No. 60/532,485, filed Dec. 24, 2003, the disclosure of which is fully incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60532485 | Dec 2003 | US |
