Abstract:
An ophthalmologic appliance being an ultrasound probe positioning immersion shell for use in ultrasonic measurement of axial length of the eye ophthalmology and other procedures. Support members in an upper chamber and a lower chamber each provides accommodating support along and about a central axis of the ultrasound probe positioning immersion shell and about vertically spaced regions of ultrasound probes to provide for perpendicular alignment of ultrasound probes to the corneal plane. Vents in the chamber structure allow for introduction of fluid medium and for the expelling of air from the chambers to inhibit bubble formation.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
   None. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is an ultrasound probe positioning immersion shell that positions and aligns a diagnostic or therapeutic device, such as an ultrasound transducer probe, for the purpose of immersion of the eye for ultrasound axial length measurement, anterior chamber depth measurement, retinal detail measurement, or other diagnostic or therapeutic applications requiring alignment with the long axis of the eye. 
   2. Description of the Prior Art 
   There are several situations in the treatment of an ophthalmic patient that require a diagnostic ultrasound examination providing detailed information of the anatomical structures of the eye. This information enables the physician to provide the best possible care for a large variety of ocular disorders. 
   The most frequent use of ultrasound in ophthalmology is the axial eye length A-scan used to measure the eye prior to cataract surgery. A synonym for this type of A-scan is biometry. This measurement of an eye&#39;s axial length provides one of the three important values needed to calculate the appropriate power of an intraocular lens (IOL) implant after cataract removal. An inaccurate axial length measurement of just one millimeter can result in a post-operative optical error of three diopters, enough to necessitate a second surgery. Cataract removal and insertion of an intraocular lens (IOL) is performed over 1.5 million times a year in the U.S. 
   Two of the most commonly used techniques to perform axial eye length measurements are as follows:
         a. Applanation, a contact technique; and,   b. Immersion, an ultrasound, non-contact technique.       

   With the contact method, the axial length is measured with the ultrasound probe applanated on the center of the cornea. The biometrist must ensure that neither ointment nor excess fluid (e.g., anesthetic drops or tears) are present on the cornea prior to beginning the examination, since even a small amount of fluid may lead to erroneous axial length readings. The contact technique can be performed by applanation (chin rest method) or by hand (hand-held method). Disadvantages of the contact technique include both corneal compression and the possibility of corneal abrasion. The anterior chamber depth must be evaluated in each echogram since shallowing of the chamber occurs when the cornea is indented. Further, due to examiner parallax or alignment problems, it is often difficult to be sure measurements are taken from the center of the cornea. 
   The immersion non-contact biometry method is the preferred method of accurately measuring the length of the eye using a special shell that provides a liquid bath between the front surface of the eye (cornea) and the measuring ultrasound probe. The unique feature about the immersion method is that the ultrasound probe never actually touches the eye. This has value since one of the most common errors made while performing an applanation (contact) axial eye length A-scan is the compression or flattening of the cornea, producing a falsely short measurement. This technique is also best for patients with blepharospasm and fixation difficulties. 
   The three fundamental advantages of the immersion method are the following:
         a. the capability to prevent inaccuracies due to corneal compression by eliminating the need to touch the cornea;   b. the capability to reproduce the measurement more readily; and,   c. the capability to use echoes from the cornea for aligning the sound beam along the visual axis, thereby providing additional assurance of a measurement to the macula.       

   With the advancement in IOL design and manufacturing, a more precise axial length measurement of the eye is required for determining the correct IOL power required for optimal pseudophakic correction. An inaccurate axial length measurement of only 1 mm can result in a significant post-operative refractive error. The ultrasound manufacturers have improved the A-scan equipment with upgraded hardware and software for measuring eye length with the transducer immersed in a liquid medium. The biometry instrument converts the time readings into millimeter axial length. When using the immersion technique, these A-scan improvements require that the ultrasound probe tip be placed at a fixed and specified distance from the corneal surface. For accurate measurements, it is essential that the ultrasound probe remains perpendicular to the visual axis while the transducer is submersed. It is equally important for the liquid medium between the corneal surface and the transducer to be free of trapped air bubbles. The presence of air bubbles can disrupt the sound wave transmission and interfere with axial length measurement. 
   To keep the eye submersed in a liquid medium during biometry, various cylindrical shells of different shapes are used in immersion A-scan. All have shortcomings. 
   Hansen Shell 
   The Hansen shell is simply a plastic cylinder open at both ends incorporated in a two-handed procedure requiring skill to master. The Hansen shell is inserted under the eyelids and hand-held while the liquid medium is poured from the top submerging the transducer and eye. Because the ultrasound probe is free to move, it can be easily moved vertically and tilted, resulting in erroneous measurements. Further, a viscous solution, Goniosol, is required, which is expensive and leaves a vision-blurring film. Achieving accurate measurements using this shell design is difficult to master. 
   Kohn Shell 
   The Kohn shell has an hourglass shape with the ultrasound probe inserted to the constriction. A port including a metal tube and hose is located at the bottom portion or lower chamber of the shell for introducing the liquid medium. The ultrasound probe and shell meet at one location with a larger diameter opening at the top of the shell. This can result in vertical and angled error due to a single fulcrum contact point, as with mating two cones with different dimensions and angles. Any dimensional difference between the ultrasound probe shape and the shell constriction increases the likelihood for the ultrasound probe to be tilted and/or positioned at a different height. 
   This Kohn shell design forms two chambers once the ultrasound probe is inserted, and a “cork effect” occurs at the contact point between the ultrasound probe and shell constriction. The liquid medium then must be injected after the shell is on the eye through the port located in the lower chamber between the constriction and the bottom of the shell contacting the eye. This reduces the ability to visually place the shell and ultrasound probe on the eye due to the port and any connected tubing blocking the view. Furthermore, due to the ultrasound probe blocking the air from escaping from the lower chamber, a large air bubble can be easily trapped in the lower chamber and prevent an ultrasound axial length measurement. 
   Prager Scleral Shell 
   Another current design is the Prager scleral shell. This is a polycarbonate plastic cylinder with a flanged end that contacts the eye. To accommodate the ultrasound probe, the upper portion of the shell is bored out in the center with an inner diameter slightly larger than the ultrasound probe to maintain orientation. A setscrew located at the top of the shell is then tightened against the probe to preclude the probe from protruding out the shell bottom and potentially contacting the cornea. The probe tip can be placed at any height from the cornea. This requires the operator to carefully inspect the ultrasound probe height position before every ultrasound exam. If the ultrasound probe tip is either too low or too high, a faulty reading will occur. Furthermore, the ultrasound probe can be easily canted from the perpendicular position in the shell when the setscrew is tightened. To fill the shell with the liquid medium, a metal port or filler tube is press fit into the shell wall. The metal port or filler tube is inserted into PVC tubing or a butterfly needle is inserted into the metal port or filler tube. Any sharp object in close proximity to the eye is considered a safety issue. Typically, multiple holes are drilled into the wall of the lower portion of the shell for air to escape as the liquid enters the lower portion of the shell. 
   SUMMARY OF THE INVENTION 
   The general purpose of the present invention is to provide an ultrasound probe positioning immersion shell. To achieve the objectives for correct ultrasound probe positioning during immersion A-scan, an ultrasound probe positioning immersion shell, a unique immersion shell, has been developed. The ultrasound probe positioning immersion shell consistently places the ultrasound probe perpendicular to and at the correct distance from the corneal plane. The ultrasound probe positioning immersion shell has a fluid flow arrangement to ensure suitable filling of a lower chamber while minimizing air bubble formation which can disrupt or otherwise influence the ultrasound measuring process. The preferred methods to achieve the perpendicular ultrasound probe position are to have one continuous guide or, preferably, to have two or more separate opposed guide rings which can be externally and internally located with each having centrally located structures providing at least three arcuate guide surfaces for intimate contact with the cylindrical or tapered shape of an ultrasound probe, respectively. The configuration of each of the externally and internally located guide rings includes centrally located arcuate guide surfaces which accommodate the ultrasound probe and, additionally, at least include three vents which can be arcuate, which are offset from the centerline of the ultrasound probe positioning immersion shell, and which intersect the centrally located arcuate guide surfaces, thereby creating a scallop-like pattern. This pattern creates at least three points of ultrasound probe contact at each guide ring location and at least three vents about the intersection of the ultrasound probe and the respective external and internal guide rings. Two or more guide rings, used for positioning the ultrasound probe, result in partial defining of separate internal upper and lower chambers, where the upper chamber is between the external guide ring, the internal guide ring and an upper cylindrical body, and where the lower chamber, which is open at one end, is bounded by the internal guide ring and a lower cylindrical body and a lip. The vents in the internal guide ring allow for the transfer of liquid medium to drain from the upper chamber to the lower chamber. The external guide ring pattern allows for air pressure equalization to ambient air when liquid medium is introduced and when the ultrasound probe is centered in the external guide ring. Self-positioning of the ultrasound probe transducer is accomplished by the arcuate guide surfaces of the external and internal guide rings contacting the ultrasound probe at a minimum of two separate body regions to ensure perpendicular positioning of the ultrasound probe in the ultrasound probe positioning immersion shell. A fluid transfer port located in the upper portion of the ultrasound probe positioning immersion shell allows for various methods of filling the liquid medium. The fluid transfer port is located away from the base of the ultrasound probe positioning immersion shell so that it will be away from the eye to improve operator visualization during placement of the instrument. The ultrasound probe positioning immersion shell can be fashioned of transparent material to monitor placement on the eye and to monitor the liquid medium level. 
   The ultrasound probe positioning immersion shell self-positions the ultrasound probe in the ultrasound probe positioning immersion shell perpendicular to the ultrasound probe positioning immersion shell lower chamber lip horizontal plane and places the ultrasound probe at a specified height from the corneal surface to optimize axial length ultrasound measurement. The geometry and size of the external arcuate guide surfaces and internal arcuate guide surfaces form an automatic stop with respect to depth and also provide a safety feature that does not allow the ultrasound probe to be placed lower than the specified depth for an optimum A-scan, thereby avoiding accidental contact with the eye. After the ultrasound probe is inserted into the ultrasound probe positioning immersion shell to the automatic stop position, the ultrasound probe positioning immersion shell is then placed on the eye. Liquid medium is filled through the fluid transfer port with low pressure to eliminate the possibility of eye tissue damage from the fluid flowing into the ultrasound probe positioning immersion shell. The external and internal arcuate vents greatly reduce the possibility of air bubble formation. 
   According to one or more embodiments of the present invention, there is -provided an ultrasound probe positioning immersion shell including external and internal support including arcuate guide surfaces on external and internal guide rings for alignment with an ultrasound probe, vents located within the external and internal guide rings, upper and lower chambers for transfer or containment of liquid or other medium, a lip for contact with the limbus or area adjacent to the cornea of an eye, and a port for introduction of liquid or other medium into the ultrasound probe positioning immersion shell, as well as other features. 
   One significant aspect and feature of the present invention is an ultrasound probe positioning immersion shell which is fully vented. 
   Another significant aspect and feature of the present invention is an ultrasound probe positioning immersion shell which eliminates or minimizes air bubble formation. 
   Still another significant aspect and feature of the present invention is an ultrasound probe positioning immersion shell which incorporates sets of guide surfaces at different levels or locations to align an ultrasound probe to its central axis. 
   Yet another significant aspect and feature of the present invention is an ultrasound probe positioning immersion shell which positions an ultrasound probe at a precise distance from the corneal plane of an eye. 
   A further significant aspect and feature of the present invention is an ultrasound probe positioning immersion shell which will not allow an ultrasound probe to positionally invade a cornea of an eye. 
   Still another significant aspect and feature of the present invention is geometry which limits the travel of an ultrasound probe along the central axis and acts as a stop. 
   A still further significant aspect and feature of the present invention is an ultrasound probe positioning immersion shell which allows for liquid medium introduction at a level distant from the eye. 
   Another significant aspect and feature of the present invention is a fluid transfer port which can accommodatingly be incorporated by itself or with the use of a Luer fitting, a fitted filler tube, an integral molded rigid filler tube, or an integral molded rigid filler tube and permanently attached flexible filler tube. 
   Another significant aspect and feature of the present invention is an ultrasound probe positioning immersion shell which can be transparent to monitor and observe liquid medium levels. 
   An alternate embodiment of the present invention involves a one-piece ultrasound probe positioning immersion shell, the significant aspects and features of which additionally include:
         a. vertically aligned guides for contacting of and for support of an ultrasound probe where the guides include upper guide edges, lower guide edges and arcuate, angled or other geometrically configured guide edges therebetween;   b. a keeper tab for ensuring the alignment of an inserted ultrasound probe against vertically aligned guides; and,   c. a keeper tab for securing an inserted ultrasound probe within the one-piece ultrasound probe positioning immersion shell.       

   Having thus described embodiments of the present invention and pointed to significant aspects and features thereof, it is the principal object of the present invention to provide an ultrasound probe positioning immersion shell. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects of the present invention and many of the attendant advantages of the present invention will b readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof and wherein: 
       FIG. 1  is an isometric view of the ultrasound probe positioning immersion shell, the present invention; 
       FIG. 2  is a re-oriented cutaway view in partial cross section along line  2 - 2  of  FIG. 1 ; 
       FIG. 3  is a cross section view of the ultrasound probe positioning immersion shell along line  3 - 3  of  FIG. 1 ; 
       FIG. 4  is a top view of the ultrasound probe positioning immersion shell; 
       FIG. 5  is a bottom view of the ultrasound probe positioning immersion shell; 
       FIG. 6  illustrates an ultrasound probe in external alignment to the ultrasound probe positioning immersion shell which is shown in cross section along with a Luer fitting also shown in cross section; 
       FIG. 7  is a view similar to  FIG. 6  but illustrating the ultrasound probe aligned within the ultrasound probe positioning immersion shell for alignment with and for ultrasound measurements of an eye (shown schematically); 
       FIG. 8  is an isometric view of an alternative embodiment ultrasound probe positioning immersion shell; 
       FIG. 9  is a re-oriented cutaway view in partial cross section along line  9 - 9  of  FIG. 8  showing additional internally located elements of the alternative embodiment; 
       FIG. 10  is a top view of the alternative embodiment ultrasound probe positioning immersion shell; 
       FIG. 11  is a cross section view of the alternative embodiment ultrasound probe positioning immersion shell along line  11 - 11  of  FIG. 10 ; 
       FIG. 12  is a cross section view of the alternative embodiment ultrasound probe positioning immersion shell along line  12 - 12  of  FIG. 10 ; 
       FIG. 13  illustrates an ultrasound probe in external alignment to the alternative embodiment ultrasound probe positioning immersion shell; 
       FIG. 14  illustrates the mode of operation where the ultrasound probe aligns within the alternative embodiment ultrasound probe positioning immersion shell incorporating the view of  FIG. 12  for vertical alignment with and for ultrasound measurements of an eye (shown schematically); 
       FIG. 15  illustrates the mode of operation where the ultrasound probe aligns within the alternative embodiment ultrasound probe positioning immersion shell incorporating the view of  FIG. 11  for vertical alignment with and for ultrasound measurements of an eye (shown schematically); and, 
       FIG. 16  illustrates the alignment and contact of the elements of the alternative embodiment ultrasound probe positioning immersion shell with the ultrasound probe. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is an isometric view of the ultrasound probe positioning immersion shell  10 , and  FIG. 2  is a re-oriented cutaway view in partial cross section along line  2 - 2  of  FIG. 1  showing additional internally located elements of the ultrasound probe positioning immersion shell  10 . Outwardly and readily visible elements of the ultrasound probe positioning immersion shell  10  include an upper cylindrical body  12  tapering to a lower cylindrical body  14 , an external guide ring  16  extending across the upper region of the upper cylindrical body  12 , a plurality of guide surfaces  18   a - 18   n , preferably being arcuate, extending through the external guide ring  16  and having a common radius centered along the central axis  20  of the ultrasound probe positioning immersion shell  10 , a plurality of external vents  22   a - 22   n , preferably being arcuate, extending through the external guide ring  16  and having like radii offset from the central axis  20  of the ultrasound probe positioning immersion shell  10  and intersecting the plurality of guide surfaces  18   a - 18   n , a lip  24  at the lower region of the lower cylindrical body  14 , and a fluid transfer port  26  extending through the upper cylindrical body  12  to communicate with an upper chamber  28  ( FIG. 2 ) of the ultrasound probe positioning immersion shell  10 . The fluid transfer port  26  can be incorporated into use by itself or with the use of a Luer fitting, a fitted filler tube, an integral molded rigid filler tube, or an integral molded rigid filler tube and permanently attached flexible filler tube. 
   Although the guide surfaces  18   a - 18   n  are preferably arcuate, other geometrically-shaped guide surfaces, such as planar surfaces, vertical edges or other suitably located geometrically configured elements and the like being appropriately spaced from the central axis  20 , can be utilized without departing from the teachings and scope of the instant invention. Also, the external vents  22   a - 22   n  preferably are arcuate; however, other geometrically-shaped external vents incorporating planar or other geometrically configured surfaces to form external vents and the like about the plurality of guide surfaces  18   a - 18   n  and being appropriately located outwardly from and non-interfering with the function of the plurality of guide surfaces  18   a - 18   n  can be utilized without departing from the teachings and scope of the instant invention. 
   Various materials can be used in manufacturing the ultrasound probe positioning immersion shell  10 , including, but not limited to, acrylic, polycarbonate Ultem, or other plastics which can be transparent, and stainless steel, aluminum, or other metals. The ultrasound probe positioning immersion shell  10  can be manufactured by machining or injection molding. 
     FIG. 2  reveals additional elements of the ultrasound probe positioning immersion shell  10 , including an internal guide ring  30  located substantially adjacent to and interior to a tapered region  32  between the upper cylindrical body  12  and the lower cylindrical body  14  and extending across the lower region of the upper cylindrical body  12 , as well as being co-located at the upper region of the lower cylindrical body  14 . The structure of the internal guide ring  30  relates directly to that of the external guide ring  16  and opposingly aligns in a spaced relationship thereto and differs slightly in size as described herein. A plurality of guide surfaces  34   a - 34   n , preferably being arcuate, extend through the internal guide ring  30  and have a common radius centered along the central axis  20  of the ultrasound probe positioning immersion shell  10 , where such radius is appropriately less than the radius incorporated in relation to the plurality of guide surfaces  18   a - 18   n  of the external guide ring  16 . A plurality of internal vents  36   a - 36   n , preferably being arcuate, extending through the internal guide ring  30  and having like radii offset from the central axis  20  of the ultrasound probe positioning immersion shell  10  and intersecting the plurality of guide surfaces  34   a - 34   n  are also included. 
   Although the guide surfaces  34   a - 34   n  are preferably arcuate, other geometrically-shaped guide surfaces, such as planar surfaces, vertical edges or other suitably located geometrically configured elements and the like being appropriately spaced from the central axis  20 , can be utilized without departing from the teachings and scope of the instant invention. Also, the internal vents  36   a - 36   n  preferably are arcuate; however, other geometrically-shaped internal vents incorporating planar or other geometrically configured surfaces to form internal vents and the like about the plurality of guide surfaces  34   a - 34   n  being appropriately located outwardly from and noninterfering with function of the plurality of guide surfaces  34   a - 34   n  can be utilized without departing from the teachings and scope of the instant invention. 
   The external guide ring  16  and the internal guide ring  30 , the elements of which are used for positioning an ultrasound probe, partially define the separate upper chamber  28  and a lower chamber  38 , where the upper chamber  28  is bounded by the external guide ring  16 , the internal guide ring  30  and the upper cylindrical body  12 , and where the lower chamber  38 , which is open at one end, is bounded by the internal guide ring  30 , the lower cylindrical body  14 , and the lip  24  at the outer extremity of the lower cylindrical body  14 . 
   Alternatively, the internal guide ring  30  and associated elements can be located along the central axis  20  in a position proximal to the shown position, thereby varying the size, proportion and volume of the upper chamber  28  and the lower chamber  38 . As such, being still located on the upper cylindrical body  12 , the fluid transfer port  26  could be positioned more distally toward the tapered region  32  to a position distal to the internal guide ring  30 ; i.e., the internal guide ring  30  and the fluid transfer port  26  can assume different relative positions, whereby, with the elongation of the lower chamber  38 , fluid can be introduced directly into the lower chamber  38  at a point below internal guide ring  30 , but above the tapered region  32  where fluid ingress is distanced at least by the lower cylindrical body  14 . 
   A threaded hole  40  extends through the upper cylindrical body  12  to accommodate a threaded fastening device  42 , as shown in  FIG. 4 . 
     FIG. 3  is a cross section view of the ultrasound probe positioning immersion shell  10  along line  3 - 3  of  FIG. 1 . 
     FIG. 4  is a top view of the ultrasound probe positioning immersion shell  10 . Shown in particular is the relationship of the guide surfaces  18   a - 18   n  offset from the central axis  20  to the guide surfaces  34   a - 34   n  offset from the central axis  20  where the guide surfaces  34   a - 34   n  have a lesser offset from the central axis  20  than the guide surfaces  18   a - 18   n . Such a relationship provides for guidance of an ultrasound probe  44  ( FIG. 6 ) along the central axis  20  of the ultrasound probe positioning immersion shell  10  where the guide surfaces  18   a - 18   n  and  34   a - 34   n  align the ultrasound probe  44  to the central axis  20  of the ultrasound probe positioning immersion shell  10  and where such a relationship forms a geometric configuration, which, due to diminishing offsets and corresponding geometry, forms a stop to limit travel of an ultrasound probe, such as the ultrasound probe  44 , within the ultrasound probe positioning immersion shell  10 . An optional fastening device  42 , such as, but not limited to, a thumbscrew, set screw or other suitable device or the like, can be utilized in the threaded hole  40  to bear against the ultrasound probe  44 , thus providing fixation of the ultrasound probe  44  within the ultrasound probe positioning immersion shell  10 . 
     FIG. 5  is a bottom view of the ultrasound probe positioning immersion shell  10  showing the lower chamber  38  and the internal guide ring  30  in which the guide surfaces  34   a - 34   n  and the internal vents  36   a - 36   n  are located. 
     FIG. 6  illustrates an ultrasound probe  44  in external alignment to the ultrasound probe positioning immersion shell  10 . Elements of the ultrasound probe positioning immersion shell  10  are designed to support the ultrasound probe  44 , which can be incorporated into use with the ultrasound probe positioning immersion shell  10 . The ultrasound probe  44  includes a constant radius body region  46 , a tapered body region  48 , and a transducer  50  at one end of the tapered body region  48 . Shown in particular is the relationship of the guide surface  18   a  located in the external guide ring  16  to the guide surface  34   a  located in the internal guide ring  30 . Guide surface  18   a  is offset from the vertical axis  20  at a distance greater than the offset of the guide surface  34   a  from the vertical axis  20 . Correspondingly and symmetrically, as shown in previous figures, guide surfaces  18   b - 18   n  are offset the same distance in correspondence to the offset of guide surface  18   a  from the vertical axis  20 . Correspondingly and symmetrically, as shown in previous figures, guide surfaces  34   b - 34   n  are offset the same distance in correspondence to the offset of guide surface  34   a  from the vertical axis  20 . Collectively, guide surfaces  18   a - 18   n  form a structure at the external guide ring  16  for supporting the constant radius body region  46  of ultrasound probe  44 , and collectively, guide surfaces  34   a - 34   n  form a structure at the internal guide ring  30  for supporting the tapered body region  48  of ultrasound probe  44 . 
   MODE OF OPERATION 
     FIG. 7  best illustrates the mode of operation where an ultrasound probe  44  aligns within the ultrasound probe positioning immersion shell  10  for vertical alignment with and for ultrasound measurements of an eye  52  which is in contact with the lip  24  of the ultrasound probe positioning immersion shell  10 . As previously described, the constant radius body region  46  of the ultrasound probe  44  aligns to the guide surfaces  18   a - 18   n  and along the central axis  20  of the ultrasound probe positioning immersion shell  10 , and the tapered body region  48  of the ultrasound probe  44  stoppingly aligns along the central axis  20  of the ultrasound probe positioning immersion shell  10  to the guide surfaces  34   a - 34   n , a distance along the central axis  20  which is predetermined by the relationship of the guide surfaces  34   a - 34   n  to the tapered body region  48  of the ultrasound probe  44 , to position the transducer  50  of the ultrasound probe  44  the correct and suitable distance from the cornea  54  of the eye  52 . Full support of the ultrasound probe  44  is provided at several levels, thus promoting stability of the ultrasound probe  44  with respect to the ultrasound probe positioning immersion shell  10 . In particular, support of the constant radius body region  46  of the ultrasound probe  44  is provided by intimate but sliding contact with the guide surfaces  18   a - 18   n , and support of the tapered body region  48  of the ultrasound probe  44  is provided by intimate contact with the guide surfaces  34   a - 34   n . A Luer fitting  56 , which can be male or female, is suitably connected to the fluid transfer port  26  for introduction of saline solution  58  or other suitable solution. 
   The invention user can directly observe correct placement of the ultrasound probe positioning immersion shell  10  on the eye  52  since the fluid transfer port  26  of the ultrasound probe positioning immersion shell  10  to which liquid filling apparatus is connected is located appropriately on the upper cylindrical body  12  away from the lower cylindrical body  14  and away from the surface of the eye  52 . Correct placement of the ultrasound probe positioning immersion shell  10  can be further enhanced by the use of a clear plastic to form it. The use of clear plastic also enhances level monitoring of the liquid medium. The fluid transfer port  26  of the ultrasound probe positioning immersion shell  10  allows for the operator to use different means of supplying the liquid medium. Liquid medium, such as a saline solution  58 , can be filled through the fluid transfer port  26  by a syringe directly through the fluid transfer port  26 , by a syringe through a fitted filler tube connected to the transfer port  26 , by an integral molded rigid filler tube, by a vial directly attached to the fluid transfer port  26 , or by the illustrated Luer fitting  56  and a flexible filler tube attached to the fluid transfer port  26 , which is connected to a container of liquid medium (not shown), or by other suitable delivery methods known in the art. 
   Introduction and flow of saline solution  58  (liquid medium) into and within the ultrasound probe positioning immersion shell  10  is unrestricted, first into the upper chamber  28 , followed by passage or draining of saline solution  58  through the internal vents  36   a - 36   n  at the internal guide ring  30  into the lower chamber  38  for suitable immersion of the lower portions of the ultrasound probe  44 , including at least the transducer  50  and preferably other portions of the ultrasound probe  44 . As saline solution  58  enters the upper chamber  28  and subsequently the lower chamber  38 , air residing in the upper chamber  28  and the lower chamber  38  is displaced by the incoming saline solution  58  and vented and expelled without restriction from the lower chamber  38 , through the internal vents  36   a - 36   n , through the upper chamber  28 , and through the external vents  22   a - 22   n  in the external guide ring  16  at the top of the upper chamber  28 . Fully vented upper and lower chambers  28  and  38  prevent back pressure buildup so that outflow of displaced air and exclusion of bubbles is not impeded. 
   The internal vents  36   a - 36   n  disperse the liquid flow pattern and create multiple paths for both the saline solution  58  to drain in one direction and for air to escape in another direction to and from the lower chamber  38 , minimizing air bubble formation in the lower chamber  38  to provide bubble-free saline solution  58  between the transducer  50  of the ultrasound probe  44  and the cornea  54  and surrounding surface of the eye  52 . 
     FIG. 8  is an isometric view of a one-piece ultrasound probe positioning immersion shell  60 , an alternative embodiment, and  FIG. 9  is a re-oriented cutaway view in partial cross section along line  9 - 9  of  FIG. 8  showing additional internally located elements of the alternative embodiment. The one-piece ultrasound probe positioning immersion shell  60  preferably is molded of a suitable plastic material, preferably a clear plastic material, thus being able to utilize high output production techniques at a lower per unit cost than that of labor intensive machined ultrasound probe positioning immersion shells. Outwardly and readily visible elements of the ultrasound probe positioning immersion shell  60  include an upper cylindrical body  62  tapering to a lower cylindrical body  64  via a tapered intermediate body  66 , a plurality of guides  68   a - 68   b  the greater portions of which extend inwardly from the upper cylindrical body  62  and smaller portions of which extend from portions of the tapered intermediate body  66  and the lower cylindrical body  64 , and inwardly facing upper guide edges  70   a  and  71   a  located on the inner edges of the guides  68   a - 68   b  and offset from the central axis  74  for aligned contact with portions of an ultrasound probe  72 , shown later in detail, being substantially in parallel alignment to the central axis  74  of the ultrasound probe positioning immersion shell  60  and in common to the locus of a radius centered along the central axis  74  of the ultrasound probe positioning immersion shell  60 . Also shown is one end of a keeper tab  76  aligned substantially perpendicular and flexibly to the central axis  74  of the ultrasound probe positioning immersion shell  60 , a lip  78  at the lower region of the lower cylindrical body  64 , a fluid transfer port  80  extending through the upper cylindrical body  62  to communicate with an upper chamber  82  of the ultrasound probe positioning immersion shell  60 , and a slot  84 , the upper portion of which is open, extending through the upper region of the upper cylinder body  62 . Grouped individual external and internal vents, such as previously described, are not included in this alternative embodiment; rather, the same venting function is provided by the interior of the upper cylindrical body  62 , the tapered intermediate body  66 , and the lower cylindrical body  64  and the lip  78 , which offer and form a large vent  86  extending along and about the central axis  74  being bounded by the upper cylindrical body  62  and the tapered intermediate body  66  which form the upper chamber  82 , and by the lower cylindrical body  64  and lip  78  which form a lower chamber  88  and, of course, by the interceding guides  68   a - 68   b  and the keeper tab  76  and a keeper tab arm  90  ( FIG. 9 ). 
   Various materials can be used in manufacturing the ultrasound probe positioning immersion shell  60 , including, but not limited to, plastics which can be clear, plastics including acrylic, polycarbonate Ultem, or other plastics, and stainless steel, aluminum, or other metals. The ultrasound probe positioning immersion shell  60  can be manufactured by machining or preferably by injection molding. 
     FIG. 9  in cross section reveals additional elements of the ultrasound probe positioning immersion shell  60  including the lower chamber  88  and the keeper tab arm  90 , as well as other structure.  FIG. 9  shows the upper cylindrical body  62 , the tapered intermediate body  66 , the lower cylindrical body  64 , and the lip  78  which form the upper and lower chambers  82  and  88 , respectively, which are open at opposing ends and which are in mutual communication where the upper chamber  82  is formed by and encompassed by the upper cylindrical body  62  and the tapered intermediate body  66  in combination, and where the lower chamber  88  is formed by and encompassed by the lower cylindrical body  64  and the lip  78  in combination. 
   The guides  68   a - 68   b , the keeper tab  76 , and the keeper tab arm  90  extend inwardly into the upper chamber  82  and portions of the lower chamber  88  from the surrounding structure, as previously described, thereby also extending into the vent  86 . The guide  68   a , in addition to the upper guide edge  70   a , also includes a lower guide edge  70   c  offset less than the offset of the upper guide edge  70   a  from the central axis  74  and being substantially in parallel alignment to the central axis  74  of the ultrasound probe positioning immersion shell  60  and in common to the locus of the lesser radius being offset less than the offset of the upper guide edge  70   a  from the central axis  74 . An arcuate guide edge  70   b  is located between the upper guide edge  70   a  and the lower guide edge  70   c . The guide  68   b  is fashioned similarly and includes an upper guide edge  71   a , a lower guide edge  71   c , and an interceding arcuate guide edge  71   b . The guides  68   a  and  68   b , including the guide edges described above, provide guidance and support for the ultrasound probe  72 , as later described in detail. 
   Although the upper, arcuate, and lower guide edges  70   a - 70   c  and  71   a - 71   c , respectively, are shown in their respective geometrical shapes, other geometrically-shaped guide edges, such as arcuate surfaces, vertical edges, or other suitably located geometrically configured elements separately or in combination and the like being appropriately and similarly spaced from the central axis  74 , can be utilized to accommodate the particular geometrical configuration of an ultrasound probe; i.e., the arcuate guide edges  70   b  and  71   b  could be angled surfaces or notched surfaces or other geometric configurations to suitably mate with and stoppingly accommodate the ultrasound probe geometrical configuration, without departing from the teachings and scope of the instant invention. 
     FIG. 10  is a top view of the ultrasound probe positioning immersion shell  60  illustrating the offset of the upper guard edge  70   a  and the upper guard edge  71   a  from the central axis  74  and of the lesser offset of the lower guard edge  70   c  and the lower guard edge  71   c  from the central axis  74 . Also shown is the vent  86  extending along and about the central axis  74 . Also shown is the keeper tab  76  in angular opposition to the guides  68   a  and  68   n.    
     FIG. 11  is a cross section view of the ultrasound probe positioning immersion shell  60  along line  11 - 11  of  FIG. 10  showing the keeper tab  76  and the keeper arm  90  which supports the keeper tab  76 . The keeper arm  90 , which is flexible, is angled inwardly toward the central axis  74  in order to springingly and forcibly engage the ultrasound probe  72  by the interceding keeper tab  76 , such as shown in  FIG. 15 . The keeper tab  76  includes an arcuate surface  76   a  which serves multiple uses, as shown in and as described in connection with  FIG. 15 . 
     FIG. 12  is a cross section view of the ultrasound probe positioning immersion shell  60  along line  12 - 12  of  FIG. 10  showing the profile of the guide  68   a  including the upper guide edge  71   a , the arcuate guide edge  71   b  and the lower guide edge  71   c  where the profile of the guide  68   a  and  68   b  are geometrically similar. 
   During insertion of a probe, such as ultrasound probe  72 , the arcuate guide surface(s)  71   b  and  70   b  urge the lower region of the ultrasound probe  72  toward and into alignment along the central axis  74  of the ultrasound probe positioning immersion shell  60 , as well as offer support to the ultrasound probe  72 . Additional support of the ultrasound probe  72  is described later in detail. 
     FIG. 13  illustrates an ultrasound probe  72  in external alignment to the ultrasound probe positioning immersion shell  60 . Elements of the ultrasound probe positioning immersion shell  60  support the ultrasound probe  72  which is shown exterior to and which can be incorporated into use with the ultrasound probe positioning immersion shell  60 . The ultrasound probe  72 , as could other suitable probes, includes geometrically-shaped elements which are fittingly accommodated and positively engaged by the ultrasound probe positioning immersion shell  60 , including elements of varying size and radii aligned along a central axis; however, other suitably-shaped elements incorporating other geometric configurations can be incorporated and shall not be deemed to be limiting as to the scope of ultrasound probes that can be incorporated into use with the present invention. One ultrasound probe that can be incorporated into use with the ultrasound probe positioning immersion shell  60 , such as the ultrasound probe  72 , is shown for purposes of demonstration and example, and includes an arrangement of geometrically configured elements including a lower constant radius body region  92  being generally cylindrical in shape, an arcuate annular region  94  extending from the lower constant radius body region  92 , an annulus  96  having a smooth radiused edge extending from the arcuate annular region  94 , an annular groove  98  extending from the annulus  96 , an annulus  100  having smooth radiused edges extending from the annular groove  98 , an upper constant radius body region  102  being generally cylindrical in shape extending from the annulus  100 , and a transducer  104  at one end of the lower constant radius body region  92 . Also included is a cable housing  106  and a passageway  108  for the conveyance of connection wire from the transducer  104  to external monitoring equipment. 
   MODE OF OPERATION 
     FIGS. 14 ,  15  and  16  best illustrate the mode of operation of the alternative embodiment where an ultrasound probe  72  aligns within the ultrasound probe positioning immersion shell  60  for vertical alignment with and for ultrasound measurements of an eye  110 , including a cornea  112  where the limbus or area adjacent to the cornea  112  is in contact with the lip  78  of the ultrasound probe positioning immersion shell  60 . 
   Insertion and guidance of the ultrasound probe  72  is initiated by alignment of the lower constant radius body region  92  with the ultrasound probe positioning immersion shell  60 , such as indicated in  FIG. 13 . 
     FIG. 14  is the same view of the invention shown in  FIG. 12  showing the accommodation of an ultrasonic probe, such as ultrasound probe  72 . During insertion of the ultrasound probe  72 , the lower constant radius body region  92  is initially guided and urged in one or more of several contactual situations. One such situation is where the lower constant radius body region  92  and/or the arcuate annular region  94  slidingly and guidingly can contact the keeper tab  76  ( FIG. 15 ) and be urged toward and in a direction along the central axis  74 . Such previous contact situation, which does not always occur but which can occur, is generally followed by the following contactual situation which can occur by itself or in following of the first contactual situation. Such a contactual situation is where the lower constant radius body region  92  and/or the arcuate circular region  94  can slidingly and guidingly contact the upper guide edge  70   a  and/or the upper guide edge  71   a , where the lower constant radius body region  92  and/or the arcuate circular region  94  can slidingly and guidingly contact either or both of the arcuate guide edges  70   b  and/or  71   b  (arcuate guide edge  70   b  not shown), where the lower constant radius body region  92  slidingly and guidingly contacts the lower guide edge  71   c  and the lower guide edge  70   c  (lower guide edge  70   c  not shown) for guided and urged positioning toward and in a direction along the central axis  74 . Any of the above situations separately, together, or in concert, guide, align and or support the ultrasound probe  72  in a position along and about the central axis  74 , such as shown in  FIG. 14 , where the guides  68   a  and  68   b  provide support for an ultrasound probe, such as ultrasound probe  72 . More specifically, the ultrasound probe  72  is supported at two or more elongated sites where the lower guide edges  70   c  and  71   c  provide for support of the lower constant radius body region  92 , where the arcuate guide edges  70   b  and  71   b  provide for support of the arcuate annular region  94 , and where the upper guide edges  70   a  and  71   a  provide for support of the annulus  96  and the annulus  100 .  FIG. 16  illustrates the alignment and contact of the elements of the ultrasound probe positioning immersion shell  60  with the ultrasound probe  72 . Additional support and a securing means is also utilized with respect to  FIG. 15 . 
     FIG. 15  is the same view of the invention shown in  FIG. 11  showing the securing of an ultrasonic probe, such as ultrasound probe  72 , within the ultrasound probe positioning immersion shell  60 . The keeper tab  76 , including arcuate surface  76   a , performs several uses and functions. One such use and function is for possible insertion and placement assistance of the lower region of ultrasound probe  72  by the keeper tab  76  during probe insertion into the ultrasound probe positioning immersion shell  60 , as previously described. Another use and function is to forcibly secure the ultrasound probe  72  within the ultrasound probe positioning immersion shell  60 ; and another use and function is to force the ultrasound probe  72  against the guides  68   a  and  68   b  of the ultrasound probe positioning immersion shell  60  for alignment. 
   The ultrasound probe  72  is inserted into the ultrasound probe positioning immersion shell  60 , as previously described, where during such insertion and alignment the keeper tab  76  is held toward the central axis  74  by the keeper arm  90 . When the keeper tab  76  is in sliding contact with the transiting ultrasound probe  72 , the keeper arm  90 , which is oriented inwardly, maintains a position and orientation toward the central axis  74 , so that the keeper tab  76  contacts the lower constant radius body region  92 . Then, the keeper tab  76  subsequently and slidingly contacts the arcuate annular region  94 , and finally intimately comes into forced tangential contact with the annulus  96  and the annulus  100  to reside generally in the annular groove  98  therebetween to force the probe  72  toward firm accommodated engagement with the guides  68   a  and  68   b  and appropriate elements thereof. 
   As previously described, the lower constant radius body region  92  of the ultrasound probe  72  aligns to the guide edges of the guides  68   a - 68   b  and along the central axis  74  of the ultrasound probe positioning immersion shell  60  a distance along the central axis  74  which is predetermined by the relationship of the arcuate guide edges  70   b  and  71   b  to the arcuate annular region  94  and the length of the lower constant radius body region  92  of the ultrasound probe  72  to position the transducer  104  of the ultrasound probe  72  the correct and suitable distance from the cornea  112  of the eye  110 . Correspondingly, the arcuate edge guides  70   b  and  71   b  act as stops which stoppingly engage the arcuate annular region  94  of the ultrasound probe  72 . Full support of the ultrasound probe  72  is provided at several areas, promoting stability of the ultrasound probe  72  with respect to the ultrasound probe positioning immersion shell  60 , as described. 
   A filler tube  114 , such as shown in  FIG. 15 , can frictionally engage the fluid transfer port  80 , or can frictionally engage and incorporate adhesive to permanently secure to the fluid transfer port  80  for introduction of saline solution or other suitable solution, such as, but not limited to, such method previously described. The invention user can directly observe correct placement of the ultrasound probe positioning immersion shell  60  on the eye  110  since the liquid filling apparatus and the fluid transfer port  80  of the ultrasound probe positioning immersion shell  60  are located on the upper cylindrical body  62  away from the lower cylindrical body  64  and away from the surface of the eye  110 . Correct placement of the ultrasound probe positioning immersion shell  10  can be further enhanced by the use of a clear plastic to form the structure of the invention. The use of clear plastic also enhances level monitoring of the liquid medium. The fluid transfer port  80  of the ultrasound probe positioning immersion shell  60  allows for the operator to use different means of supplying the liquid medium. Liquid medium, such as a saline solution, can be filled through the fluid transfer port  80  by a syringe through the fluid transfer port  80  or by a syringe through the filler tube  114 . Alternatively, the fluid transfer port  80  could be simply a hole, such as the fluid transfer port  26  shown in  FIGS. 1 and 2 , and utilized in the same fashion incorporating the use of the hole itself as an injection port, or by the use of other devices connected thereto, thereby incorporating the use of a Luer fitting, a fitted filler tube, a vial directly attached to the fluid transfer port  80 , a Luer adapter and tubing attached to the fluid transfer port  80  which is connected to a container of liquid medium, or by other suitable delivery methods known in the art. 
   Introduction and flow of saline solution (liquid medium) into and within the ultrasound probe positioning immersion shell  60  is unrestricted, first into the upper chamber  82 , followed by passage or draining of saline solution through and along the vent  86  into the lower chamber  88  for suitable immersion of the lower portions of the ultrasound probe  72 , including at least the transducer  104  and preferably other portions of the ultrasound probe  72 . As saline solution enters the upper chamber  82  and subsequently the lower chamber  88 , air residing in the upper chamber  82  and the lower chamber  88  is displaced by the incoming saline solution and vented and expelled without restriction from the lower chamber  88 , and through the upper chamber  82 , and through the top of the upper chamber  82  (i.e., through the vent  86 ). Fully vented upper and lower chambers  82  and  88  prevent back pressure buildup so that outflow of displaced air and exclusion of bubbles is not impeded. 
   The large volumetric capacity of the internal vent  86  disperses the liquid flow pattern and creates a sufficiently large path for the saline solution to drain in one direction and for air to escape in another direction to and from the lower chamber  88  simultaneously, thereby minimizing air bubble formation in the lower chamber  88  to provide bubble-free saline solution between the transducer  104  of the ultrasound probe  72  and the cornea  112  and surrounding surface of the eye  110 . 
   Various modifications can be made to the present invention without departing from the apparent scope thereof.