Ophthalmologic Applanation Prism Replacement System for Eye Examining Instrument

Abstract

A replaceable prism for an eye examining instrument is made to be discarded after each use. A bendable tab molded on the prism is deformed by a strain gauge as the prism is inserted into a prism holder, and a signal from the strain gauge is used to verify that a previously unused prism has been inserted into the holder. A microprocessor is programmed to recognize the signal produced by initial deformation of the prism tab so as to proceed with an eye examination only after receiving the strain gauge signal verifying that a previously unused prism has been inserted.

1 . A system ensuring replacement of a molded resin prism used in an eye examining instrument having a microprocessor and a holder for receiving the prism in an operating position, the system comprising: 
 the prism being molded to have an element that is deformable in a direction of insertion of the prism into the holder;    a strain gauge arranged in the holder to engage the element as the prism is being inserted into the holder and before the prism reaches the operating position;    the strain gauge being arranged to deform the element from its initial position to a deformed position as the prism is moved fully into the holder to the operating position;    the strain gauge being arranged to produce a strain signal delivered to the microprocessor representing the strain involved in deforming the element from its initial position to its deformed position;    the element being configured so that a first deformation of the element from its initial position to its deformed position requires more stress than any subsequent deformation of the element from its initial position to its deformed position;    the microprocessor being programmed to distinguish between a strain signal from the strain gauge representing the first deformation of the element and a strain signal from the strain gauge representing the subsequent deformation of the element; and    the microprocessor being programmed to proceed with an eye examination only if a prism inserted into the holder causes the strain gauge to produce a strain signal representing the first deformation of the element.    
   
   
       2 . The system of  claim 1  wherein the prism has a location projection that detents in the holder when the prism is in the operating position.  
   
   
       3 . The system of  claim 1  wherein the element is a bendable tab and the deformation is a bending of the tab.  
   
   
       4 . The system of  claim 1  wherein the prism has a grippable tab by which the prism is inserted into the holder.  
   
   
       5 . An eye examining instrument having a microprocessor and a prism holder combined with a molded resin prism insertable into the holder in a way that requires prism replacement before proceeding with an eye examination, the combination comprising: 
 the prism being molded with an element extending transversely of a direction of insertion of the prism into the holder;    the element being deformable from an initial position to a deformed position as the prism is inserted into the holder and into an operating position within the holder;    the element being configured so that a first deformation of the element requires more stress than any subsequent deformation of the element;    the holder including a strain gauge positioned to engage and deform the element as the element is inserted into the holder;    the strain gauge being arranged to produce a signal representing the strain encountered in deforming the element as the prism is inserted into the holder;    the microprocessor being programmed to recognize the strain gauge signal representing the first deformation of the element;    the microprocessor being programmed to proceed with an eye examination whenever insertion of a prism into the holder causes the strain gauge to produce the signal representing the first deformation of the element; and    the microprocessor being programmed not to proceed with an eye examination whenever insertion of a prism into the holder causes the strain gauge to produce a signal distinguishably smaller than the signal representing the first deformation of the element.    
   
   
       6 . The combination of  claim 5  wherein the prism has a locator projection that seats in the holder in a detented position when the prism is in its operating position.  
   
   
       7 . The combination of  claim 5  wherein the prism has a gripping tab by which the prism is inserted into the holder.  
   
   
       8 . The combination of  claim 5  wherein the element is a hinged tab.  
   
   
       9 . A method of ensuring that a molded resin prism is replaced in an eye examining instrument before each eye examination, the method comprising: 
 forming prism replacements that each have a tab that is initially deformable in response to a predetermined stress;    inserting one of the prism replacements into a prism holder of the instrument so that the deformable tab engages a strain gauge in the holder and becomes deformed by the strain gauge as the prism is moved into an operating position within the instrument;    using the strain gauge to produce a signal representing the strain encountered in initially deforming the tab as the prism is inserted into the holder;    transmitting the strain gauge signal to a microprocessor in the instrument and programming the microprocessor to recognize the strain gauge signal representing the initial deformation of the tab; and    programming the microprocessor to proceed with an eye examination only upon receiving the strain gauge signal representing the initial deformation of the tab.    
   
   
       10 . The method of  claim 9  including programming the microprocessor not to proceed with an eye examination and to indicate to the instrument user upon receiving a strain gauge signal distinguishably smaller than the strain gauge signal representing initial deformation of the tab.  
   
   
       11 . A method of insuring that an eye contacting prism is replaced before each examination of a pair of eyes, the method comprising: 
 molding the prism of resin with a deformable element that is deformable to a predetermined extent without breaking away from the prism;    configuring the deformable element to have an initial resistance to an initial deformation to the predetermined extent and a reduced resistance to any subsequent deformation to the predetermined extent;    arranging a strain gauge within an eye examining instrument to measure deformation resistance of the deformable element as the prism is inserted in the instrument;    arranging the strain gauge to produce a strain signal delivered to a microprocessor in the instrument as representative of the deformation resistance of the deformable element; and    programming the microprocessor to proceed with the examination of the pair of eyes only when the strain signal coincides with the strain representing the initial resistance.    
   
   
       12 . The method of  claim 11  including programming the microprocessor not to proceed with the examination of the pair of eyes and to indicate to the instrument user when the strain signal distinguishably differs from the strain representing the initial resistance.  
   
   
       13 . An eye examining instrument and an eye contacting prism combined to ensure replacement of the prism before proceeding with examination of a pair of eyes, the combination comprising: 
 the prism having a deformable element configured to have a larger resistance to an initial deformation and a smaller resistance to a subsequent deformation;    the instrument having a strain gauge arranged to cause deformation of the deformable element as the prism is inserted into the instrument;    a microprocessor in the instrument receiving a deformation signal from the strain gauge and being programmed to recognize an initial deformation signal corresponding to the strain encountered during the initial deformation of the deformable element; and    the microprocessor being programmed to proceed with the examination of the pair of eyes only upon receiving the initial deformation signal.    
   
   
       14 . The combination of  claim 13  wherein the deformable element is a bendable tab oriented transversely to a direction of insertion of the prism into the instrument.  
   
   
       15 . The combination of  claim 13  wherein the deformable element is configured not to break away from the prism.  
   
   
       16 . The combination of  claim 13  wherein the prism includes a location projection that snap fits into a seated position when the prism is in an operating position within the instrument.  
   
   
       17 . A disposable molded resin prism useable in an eye examining instrument, the prism comprising: 
 a bendable tab formed of the molded resin of the prism to extend from a body of the prism;    the tab being configured to be bent from an initial position to a bent position as the prism is inserted into the instrument;    the tab being formed to survive bending without breaking off from the prism body during insertion of the prism into the instrument and removal of the prism from the instrument for disposal; and    the tab being formed to have a resistance to an initial bending to the bent position that is larger than any resistance of the tab to a subsequent bending to the bent position.    
   
   
       18 . The prism of  claim 17  wherein the tab is formed with a thin hinge line allowing the tab to bend.  
   
   
       19 . The prism of  claim 17  wherein the tab extends from a non-optical surface of the prism body.  
   
   
       20 . The prism of  claim 17  wherein the tab extends transversely of the direction of insertion of the prism into the instrument.