Abstract:
A cylinder axis control knob for a lens battery of a subjective ophthalmic refractor comprises at least one shaped pointer formed integrally with the knob to avoid assembly problems associated with printed pointers on the knob and provide a better indication to the operator.

Description:
FIELD OF INVENTION  
         [0001]    The present invention relates generally to the field of ophthalmic instruments, and more particularly to subjective ophthalmic refractors for evaluating refractive characteristics of a patient&#39;s eye.  
         BACKGROUND OF THE INVENTION  
         [0002]    Subjective ophthalmic refractors of the prior art typically comprise left-eye and right-eye lens batteries each having a defined viewing path along which an operator selectively introduce one or more testing lenses having known refractive properties. During examination, the patient is positioned in a darkened room with his or her eyes aligned to view a projected target chart along the viewing paths of the left-eye and right-eye batteries. The operator then performs well-known refracting procedures, including refraction using astigmatic charts and the Jackson cross-cylinder test. A goal of the examination procedure is to determine the sphere power, cylinder power, and cylinder axis of each eye so that suitable corrective lenses may be prescribed.  
           [0003]    With specific regard to determining the cylinder axis, it is well known to provide a rotatable cylinder axis control knob that is mechanically connected through a gear train to rotatable lens cells which hold cylinder testing lenses selectively aligned in the viewing path. When the cylinder axis control knob is rotated, a corresponding 1:1 rotation of the cylinder lens cells occurs, thereby causing the angular orientation of the cylinder axis to change. A fixed angular scale is arranged coaxially with the rotated lens cells on the viewing path, or coaxially with the cylinder axis adjustment knob. In the former arrangement, two diametrically opposite index pointer markings are applied to an outer cylinder lens in alignment with the true cylinder axis, and the pointer markings rotate with the lens cell relative to the fixed angular scale to visually indicate the precise angular orientation of the cylinder axis. An example of this type of arrangement is found in U.S. Pat. No. 2,968,213. In the latter arrangement, two diametrically opposite index pointer markings are applied to the cylinder axis adjustment knob for rotation relative to the fixed angular scale. An example of this latter type of arrangement, as well as the former type, is found in the Ultramatic RX Masters™ PHOROPTOR® refracting instrument and the Illuminated PHOROPTOR® refracting instrument offered by Reichert Ophthalmic Instruments, a division of Leica Microsystems Inc.  
           [0004]    Under current manufacturing procedure, pointer markings are applied to an annular flange on the cylinder axis control knob by a printing process. A problem recognized by applicant is that limitations in the precision and accuracy of the printing process cause slight variations in the position of the pointer markings relative to the control knob and to each other. Consequently, during assembly, a technician often must try several knobs to find an acceptable knob having pointer markings in correct alignment with the fixed angular scale markings and with each other. This slows assembly and adds cost to the instrument.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    Therefore, it is an object of the present invention to provide a cylinder axis control knob that can be manufactured in production lots without giving rise to downstream assembly delays associated with difficulties in aligning the cylinder axis pointers relative to an angular cylinder axis scale on a refractor lens battery.  
           [0006]    The present invention is embodied in a subjective ophthalmic refractor lens battery having a viewing path, means for positioning at least one cylinder lens in the viewing path, a rotatable cylinder axis control knob operatively connected to the cylinder lens or lenses for rotating same about the viewing path in response to rotation of the cylinder axis control knob, and an angular cylinder axis scale coaxial with the cylinder axis control knob. In accordance with a preferred embodiment of the present invention, the cylinder axis control knob includes two integrally formed and diametrically opposite pointers that extend in a radial direction of the knob and overlap with the cylinder axis scale. The pointers are preferably tapered in three dimensions to provide an accurate reading regardless of the angle at which the operator views the cylinder axis scale and superimposed pointers. A recess is preferably provided near each pointer in alignment with a radial direction of the pointer for receiving paint or other marking material. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    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:  
         [0008]    [0008]FIG. 1 is a front elevational view of a subjective ophthalmic refractor formed in accordance with a preferred embodiment of the present invention;  
         [0009]    [0009]FIG. 2 is a front elevational view of a right-eye lens battery of the ophthalmic refractor shown in FIG. 1;  
         [0010]    [0010]FIG. 3 is a perspective view of a cylinder axis control knob of the lens battery shown in FIG. 2;  
         [0011]    [0011]FIG. 4 is a top plan view of the cylinder axis control knob; and  
         [0012]    [0012]FIG. 5 is a cross-sectional view of the cylinder axis control knob taken generally along the line A-A in FIG. 4. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    Attention is directed initially to FIG. 1 of the drawings, wherein a subjective ophthalmic refractor incorporating the present invention is shown and designated broadly by the reference numeral  10 . Refractor  10  is conventional in that it generally comprises a right-eye lens battery  11 A and a left-eye lens battery  11 B that are mirror images of each other. Lens batteries  11 A and  11 B comprise respective housings  12 A and  12 B, as well as respective viewing paths  14 A and  14 B along which a patient facing a back side of refractor  10  gazes during examination. The construction and operation of ophthalmic refractor  10  are generally and substantially as taught in U.S. Pat. Nos. 2,968,213 and 2,995,065, both these patents being incorporated herein by reference.  
         [0014]    The present invention involves the cylinder axis adjustment system found in each lens battery  11 A and  11 B. For sake of simplicity, the invention is described with respect to right-eye lens battery  11 A only, it being understood that left-eye lens battery  11 B is a mirror image of right-eye lens battery  11 A.  
         [0015]    As best seen in FIG. 2, lens battery  11 A includes a cylinder axis control knob  16  rotatable about a central axis  17  and surrounded by an angular cylinder axis scale  18  that is fixed relative to housing  12 A and positioned to be coaxial with rotational axis  17  of cylinder axis control knob  16 . Cylinder axis control knob  16  is operatively connected by way of a gear train (not shown) contained within housing  12 A to lens cells  20  aligned along viewing path  14 A. The lens cells  20 , only one of which is visible in FIG. 2, are rotatable about viewing path  14 A by way of the gear train such that rotation of cylinder axis control knob  16  causes a corresponding 1:1 rotation of lens cells  20  about viewing path  14 A. Lens cells  20  each carry a cylindrical lens  22  of known power or no lens for zero power. It is well known to those skilled in the art to align a selected cylindrical lens of relatively strong power and a selected cylindrical lens of relatively weak power along viewing path  14 A to achieve a desired resultant cylinder power for test purposes. The respective cylinder axes of cylindrical lenses  22  have the same angular orientation with respect to viewing path  14 A, and thus the cylinder axes may be referred to as simply the cylinder axis. Thus, when cylinder axis control knob  16  is rotated, the cylinder axis associated with viewing path  14 A rotates in corresponding fashion about the viewing path to change the angular orientation of the cylinder axis.  
         [0016]    The orientation of the cylinder axis is indicated on cylinder axis scale  18 . In accordance with a preferred embodiment of the present invention, and with reference to FIGS.  3 - 5 , cylinder axis control knob  16  includes a pair of pointers  24 A and  24 B integrally formed therewith and arranged in diametrically opposite relation to each other about rotational axis  17 . More specifically, knob  16  includes an annular flange  26  sloped toward cylinder axis scale  18  as the flange expands radially outward from a cylindrical main body  28  of knob  16 , and pointers  24 A and  24 B project radially outward from flange  26  to overlap with cylinder axis scale  18 . As will be appreciated, the slope of flange  26  is continued over the projecting pointers  24 A and  24 B such that the pointers can be considered to be tapered in three-dimensions rather than merely two-dimensions. This feature is important because it minimizes possible error in viewing the true location of the pointer tip on cylinder axis scale  18  due to differences in operator viewing angle.  
         [0017]    It is preferred that pointers  24 A and  24 B protrude radially from cylinder axis control knob  16  sufficiently to overlap with scale line markings located at regular angular intervals about cylinder axis scale  18 , as can be seen in FIG. 2. This gives the operator a better indication of the cylinder axis orientation, as compared with the prior art, especially when the pointers are between scale line markings. This feature is particularly helpful where the cylinder axis scale is bright and the scale markings are dark, such as when the cylinder axis scale is illuminated or is formed of photoluminescent material, as taught for example in commonly owned U.S. patent application Ser. No. 10/037326 filed Nov. 9, 2001, which patent is hereby incorporated by reference. As will be appreciated, a silhouette of each pointer will be readily visible against the illuminated or luminous scale.  
         [0018]    As an additional structural feature of the preferred embodiment, cylinder axis control knob  16  includes recesses  30 A and  30 B formed in flange  26  and aligned along a radial pointing direction of pointers  24 A and  24 B, respectively. The recesses are intended to receive paint or other marking material as an added indicator.  
         [0019]    Cylinder axis control knob  16  further includes a pair of threaded holes  32 A and  32 B extending radially through main body  28  for receiving set screws (not shown) for securing the knob to an actuating shaft (not shown) on which knob  16  is mounted. Threaded hole  30 A is angularly aligned with pointer  24 A, while threaded hole  30 B is spaced 90° from threaded hole  30 A. Currently, it is preferred to manufacture cylinder axis control knob  16  from aluminum by precision machining a length of cylindrical bar stock.