Abstract:
A model human eye suitable for practicing surgical procedures, comprising a hemispherical-shaped bottom assembly having a bowl-shaped substrate disposed therein, a retinal layer disposed on the bowl-shaped substrate, and a hemispherical-shaped top portion attached to the bottom portion, the top portion comprising a visually transparent cornea portion and a visually opaque sclera portion, wherein the cornea portion and the sclera portion are integrally molded, wherein the cornea portion comprises a posterior corneal surface, wherein a distance from the posterior corneal surface to the retinal layer is an axial length. The model human eye is particularly suited for practicing A-scan ultrasound biometry and optical coherence biometry.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation-In-Part claiming priority from U.S. Utility application Ser. No. 12/163,838, filed Jun. 27, 2008, which is a Continuation-In-Part and claims priority to U.S. Utility application Ser. No. 11/770,653 filed Jun. 28, 2007. U.S. Utility application Ser. No. 12/163,838 is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a model human eye for pedagogical use by medical professionals. 
       BACKGROUND OF THE INVENTION 
       [0003]    Medical students, interns, residents, and fellows, specializing in diagnosing and treating injuries to, and the diseases of, the eye must necessarily practice certain surgical techniques prior to actually operating on human patients. Prior art training methods often use animal eyes, such as, for example human cadaver eyes or pig eyes. 
         [0004]    The use of human cadaver and/or animal eyes (collectively “biological eyes”) is burdened with many procedural issues. The biological eyes must be refrigerated before use, and even when refrigerated suffer from a short “shelf life” due to inevitable biological decomposition. The handling of such biological eyes requires compliance with, among other regulations, the Blood Born Pathogens Standard promulgated under the federal Occupational Health and Safety Act. After use, the biological eyes must be properly disposed of. 
         [0005]    What is needed is a model human eye that closely mimics the anatomy and physiology of the human eye, but which does not require refrigeration and other special handling procedures. 
       SUMMARY OF THE INVENTION 
       [0006]    Applicants&#39; invention comprises a model human eye that can be used for surgical training purposes, and in particular for practicing A-scan ultrasound biometry and optical coherence biometry. The model human eye comprises a hemispherical-shaped bottom assembly having a bowl-shaped substrate disposed therein, a retinal layer disposed on the bowl-shaped substrate, and a hemispherical-shaped top portion attached to the bottom portion, the top portion comprising a visually transparent cornea portion and a visually opaque sclera portion, wherein the cornea portion and the sclera portion are integrally molded, wherein the cornea portion comprises a posterior corneal surface, wherein a distance from the posterior corneal surface to the retinal layer is an axial length. 
         [0007]    Applicants&#39; invention further comprises a method to practice surgical techniques on a model human eye. The method comprises providing a model human eye having a hemispherical-shaped bottom assembly having a bowl-shaped substrate disposed therein, a retinal layer disposed on the bowl-shaped substrate, and a hemispherical-shaped top portion attached to the bottom portion, the top portion comprising a visually transparent cornea portion and a visually opaque sclera portion, wherein the cornea portion and the sclera portion are integrally molded, wherein the cornea portion comprises a posterior corneal surface, wherein a distance from the posterior corneal surface to the retinal layer is an axial length. The model human eye provided is structurally suited for practicing medical procedures including A-scan ultrasound biometry and optical coherence biometry. The method further comprises practicing a medical procedure using the model human eye. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention will be better understood from a reading of the following detailed description taken in conjunction with the drawings in which like reference designators are used to designate like elements, and in which: 
           [0009]      FIG. 1  illustrates a human eye; 
           [0010]      FIG. 2  is a perspective view of Applicants&#39; model eye; 
           [0011]      FIG. 3  is a cross-sectional view of Applicants&#39; model eye showing three retinal layers; and 
           [0012]      FIG. 4  is a cross-sectional view of Applicants&#39; model showing the axial length. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    This invention is described in preferred embodiments in the following description with reference to the Figures, in which like numbers represent the same or similar elements. Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. 
         [0014]    The described features, structures, or characteristics of the invention may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are recited to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. 
         [0015]    Applicants&#39; invention comprises a model human eye that closely mimics the anatomy, physiology, and size of the human eye and is structurally suited to allow physicians to meaningfully practice surgical procedures utilizing their own equipment and instruments. By “structurally suited” Applicant means that the present invention is so configured that training methods utilizing Applicants&#39; model human eye closely mimic surgical procedures performed on actual patients. 
         [0016]    Referring now to  FIG. 1 , the human eye comprises outer layers which include the cornea and the sclera. These layers enclose an anterior chamber disposed in front of the lens, and a larger posterior chamber disposed behind the lens. The anterior chamber is filled with a watery aqueous humor, and the posterior chamber is filled with a jelly-like vitreous body. 
         [0017]    Referring now to  FIG. 2 , Applicants&#39; model human eye  100  is formed from subassemblies  105  and  130 . Sub-assembly  105  comprises cornea portion  110  and sclera portion  120 . In certain embodiments, assembly  105  is molded as an integral part. In certain embodiments, assembly  105  is formed by liquid injection molding. In certain embodiments, assembly is formed by injection molding a silicone resin. In certain embodiments, that silicone resin comprises polydimethylsiloxane. In certain embodiments, that silicone resin comprises an elastomeric polydimethylsiloxane. 
         [0018]    In certain embodiments, the portion of the mold used to form sclera portion  120  comprises a plurality of microscopic protuberances, i.e. a relatively “rough” surface microscopically. As a result, the molded sclera portion  120  diffracts visible light, and therefore, is visually opaque. In contrast, the portion of the mold used to mold cornea portion  110  does not comprise such microscopic roughness. As a result, cornea portion  110  comprises a smooth surface and does not diffract visible light, and is visually transparent. Border  107  defines the intersection of transparent cornea portion  110  and visually opaque sclera portion. 
         [0019]    Referring now to  FIG. 3 , a human cornea comprises a varying thickness, wherein that thickness is greatest at the periphery and decreases to a minimum thickness in the middle. Cornea portion  110  is formed to mimic the varying thickness of the human cornea. Cornea portion  110  comprises center point  312 . Cornea portion  110  is formed to comprise a minimum thickness between about 0.45 mm and about 0.55 mm at center point  312 . Cornea portion  110  is formed to comprise a maximum thickness of between about 0.6 mm and about 0.8 mm at periphery  314  of cornea  110 . 
         [0020]    Applicants&#39; model eye  100  further comprises iris  315  and a lenticular bag  320  disposed therein.  FIG. 3  shows iris portion  315   a  and iris portion  315   b . As those skilled in the art will appreciate, iris portions  315   a  and  315   b  are each disposed in a continuous, annular iris element, wherein that annular iris element is continuously attached to an inner surface of assembly  105  along border  107 . In certain embodiments the distal ends of iris portions  315   a  and  315   b  are separated by a distance  316 . Distance  316  can be varied. In certain embodiments, distance  316  is 8 mm. 
         [0021]    Lenticular bag  320  is continuously attached to iris  315 . Iris  315  in combination with lenticular bag  320  and with a portion of the inner surface of assembly  105  disposed above the iris define anterior chamber  310 . Anterior chamber  310  is filled with a first fluid having a first viscosity. In certain embodiments, the first fluid comprises a viscosity of water. 
         [0022]    Filled lenticular bag  320  mimics the capsule surrounding the lens in the human eye. In a normal human eye, the lens is surrounded by a capsule which separates the lens from the vitreous, which is a third fluid disposed in chamber  330  located in the back of the eye, and the aqueous, which is the first fluid disposed in anterior chamber  310  located in the front of the eye. The second fluid disposed in posterior chamber  330  comprises a second viscosity, wherein the second viscosity is greater than the first viscosity. This capsule comprises an anterior portion separating the lens from the aqueous humor, and a posterior portion separating the lens from the vitreous humor. 
         [0023]    The human eye comprises a plurality of retinal layers disposed along the posterior interior surface. Applicants&#39; model eye  100  similarly comprises a plurality of layers, namely layers  350 ,  360 , and  370 , disposed in a stack disposed on the curved surface  340  of posterior chamber  330 . In certain embodiments, layer  370  comprises a blue color. In certain embodiments, layer  360  comprises a white color. In certain embodiments, layer  350  comprises a red color. In certain embodiments, each layer  350 ,  360 , and  370 , are separately formed. In certain embodiments, layers  350 ,  360 , and  370 , comprise a thickness between about 0.0002 to about 0.0006 inches. 
         [0024]    A vitrectomy is a surgery to remove some or all of the vitreous humor from the eye and may be performed when the retina has detached from the wall of the eye. During a vitrectomy a surgeon inserts a small instrument into the eye and suctions out some or all of the vitreous gel. After the vitreous humor is removed, the surgeon may treat the retina by photocoagulation, by removing fibrous or scar tissue from the retina, by flattening areas where the retina has become detached, or by repairing tears or holes in the retina or macula. Embodiments of Applicants&#39; model human eye  100  can be used to practicing performing a vitrectomy. 
         [0025]    Referring to  FIG. 4 , in certain embodiments Applicants&#39; model human eye  100  closely mimics the dimensions of an adult human eye. In such embodiments, distance  311  from the posterior surface  309  of cornea portion  110  to the end of chamber  330 , here retinal layer  370 , of Applicants&#39; model eye  100  corresponds to the axial length of the human eye. For such embodiments distance  311  is between approximately 18 mm and approximately 33 mm. By “approximately” Applicant means±10%. In such embodiments diameter  319  at border  107  of cornea portion  110  and scleral portion  120  is greater than approximately 10.5 mm. In certain such embodiments, distance  311  is approximately 24 mm and diameter  319  is approximately 12 mm. 
         [0026]    The axial length, corresponding to distance  311  in  FIG. 4 , is a major determinant in common sight disorders and must be measured to calculate the power of an intraocular lens to be implanted following a cataract surgery. A-scan ultrasound biometry, commonly referred to as A-scan, is routinely used to measure the axial length of an eye and can employ either applanation or water immersion techniques. In performing an applanation A-scan, an anesthetic drop is instilled in the patient&#39;s eye and the patient is instructed to look at a target at the end of the probe, or transducer, which is placed directly on the cornea surface. 
         [0027]    Because the applanation probe applies pressure to the eye, some compression of the cornea will occur, which can result in an underestimate of the axial length. Typically multiple measurements are taken until an acceptable degree of consistency is obtained, however, when the corneal compression is inconsistent, the measurements can vary substantially from one another. Further inaccuracies can be introduced by the presence of a fluid meniscus between the probe tip and the cornea, which can result in a falsely long axial length. It is estimated that the difficulties in using applanation A-scan to measure the axial length result in only 25% of patients having accurate outcomes. Corneal compression and the presence of a fluid meniscus result in as much as 40% of patients having intraocular lenses which are more myopic than expected and another 25% being more hyperopic than expected. Applicants&#39; model eye  100 , preferably having at least one retinal layer, can be used to practice accurately measuring the axial length by applanation A-scan ultrasound biometry. 
         [0028]    In performing an immersion A-scan, a scleral shell, cup, or other device is placed on the eye and holds the probe a fixed distance from the cornea, surrounded by a coupling fluid. The coupling fluid can be, and without limitation, saline solution, hydroxypropyl methylcellulose, balanced salt solution, or artificial tears. While the immersion A-scan produces more accurate readings, because the probe is not in direct contact with the eye, the sound waves must pass through the coupling fluid before reaching the back of the eye, making it more difficult to judge the layers of the internal eye, especially when a dense cataract is present. Applicants&#39; model eye  100 , preferably having at least one retinal layer, can be used to practice accurately measuring the axial length by immersion A-scan ultrasound biometry. 
         [0029]    A third method for measuring the axial length of the eye is by optical coherence biometry (OCB), also termed partial coherence interferometry (PCI), laser interference biometry (LIB), or laser Doppler interferometry (LDI), which relies on a laser Doppler technique to measure the echo delay and intensity of infrared light reflected back from tissue interfaces. Applicants&#39; model eye  100 , preferably having at least one retinal layer, can be used to practice accurately measuring the axial length by OCB. 
         [0030]    In certain embodiments, Applicants&#39; invention includes a set of two or more model human eyes  100 , wherein each eye comprises a different axial length  311 . The actual axial length of each of the model eyes  100  in the set has been previously determined. 
         [0031]    Practitioners using Applicants&#39; set of model eyes are given an opportunity to access their skills using multiple model eyes, where each of the model eyes has a different known axial length. By providing model eyes having known axial lengths, and in particular known axial lengths which differ from one another, practitioners will readily be able to determine if they have correctly measured the axial length using any known technique, including, but not limited to A-scan ultrasound biometry and OCB, by comparing the known axial length with the measured axial length. 
         [0032]    While the preferred embodiments of the present invention have been illustrated in detail, it should be apparent that modifications and adaptations to those embodiments may occur to one skilled in the art without departing from the scope of the present invention as set forth in the following claims.