Abstract:
An illuminator configured to deliver white light into an optical fiber includes a pump light source and a white phosphor. The pump light source configured to emit short-wavelength light. The white phosphor is disposed to receive the short-wavelength light from the pump light source and to output white light in response to the pumping light. The white phosphor is thermally isolated from the pump light source.

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. provisional application Ser. No. 61/233,388, filed on Aug. 12, 2009, the contents which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to an illuminator for use in ophthalmic surgery and more particularly to an ophthalmic endoilluminator to produce a light suitable for illuminating the inside of an eye. 
     BACKGROUND OF THE INVENTION 
     Anatomically, the eye is divided into two distinct parts—the anterior segment and the posterior segment. The anterior segment includes the lens and extends from the outermost layer of the cornea (the corneal endothelium) to the posterior of the lens capsule. The posterior segment includes the portion of the eye behind the lens capsule. The posterior segment extends from the anterior hyaloid face to the retina, with which the posterior hyaloid face of the vitreous body is in direct contact. The posterior segment is much larger than the anterior segment. 
     The posterior segment includes the vitreous body—a clear, colorless, gel-like substance. It makes up approximately two-thirds of the eye&#39;s volume, giving it form and shape before birth. It is composed of 1% collagen and sodium hyaluronate and 99% water. The anterior boundary of the vitreous body is the anterior hyaloid face, which touches the posterior capsule of the lens, while the posterior hyaloid face forms its posterior boundary, and is in contact with the retina. The vitreous body is not free-flowing like the aqueous humor and has normal anatomic attachment sites. One of these sites is the vitreous base, which is a 3-4 mm wide band that overlies the ora serrata. The optic nerve head, macula lutea, and vascular arcade are also sites of attachment. The vitreous body&#39;s major functions are to hold the retina in place, maintain the integrity and shape of the globe, absorb shock due to movement, and to give support for the lens posteriorly. In contrast to aqueous humor, the vitreous body is not continuously replaced. The vitreous body becomes more fluid with age in a process known as syneresis. Syneresis results in shrinkage of the vitreous body, which can exert pressure or traction on its normal attachment sites. If enough traction is applied, the vitreous body may pull itself from its retinal attachment and create a retinal tear or hole. 
     Various surgical procedures, called vitreo-retinal procedures, are commonly performed in the posterior segment of the eye. Vitreo-retinal procedures are appropriate to treat many serious conditions of the posterior segment. Vitreo-retinal procedures treat conditions such as age-related macular degeneration (AMD), diabetic retinopathy and diabetic vitreous hemorrhage, macular hole, retinal detachment, epiretinal membrane, CMV retinitis, and many other ophthalmic conditions. 
     A surgeon performs vitreo-retinal procedures with a microscope and special lenses designed to provide a clear image of the posterior segment. Several tiny incisions just a millimeter or so in length are made on the sclera at the pars plana. The surgeon inserts microsurgical instruments through the incisions such as a fiber optic light source to illuminate inside the eye, an infusion line to maintain the eye&#39;s shape during surgery, and instruments to cut and remove the vitreous body. 
     During such surgical procedures, proper illumination of the inside of the eye is important. Typically, a thin optical fiber is inserted into the eye to provide the illumination. A light source, such as a metal halide lamp, a halogen lamp, a xenon lamp, or a mercury vapor lamp, is often used to produce the light carried by the optical fiber into the eye. The light passes through several optical elements (typically lenses, mirrors, and attenuators) and is emitted to the optical fiber that carries the light into the eye. The quality of this light is dependent on several factors including the types of optical elements selected. 
     SUMMARY OF THE INVENTION 
     An illuminator configured to deliver white light into an optical fiber includes a pump light source and a white phosphor. The pump light source configured to emit short-wavelength light. The white phosphor is disposed to receive the short-wavelength light from the pump light source and to output white light in response to the pumping light. The white phosphor is thermally isolated from the pump light source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features and wherein: 
         FIG. 1  illustrates the anatomy of the eye in which an ophthalmic endoilluminator in accordance with embodiments of the present invention may be placed; 
         FIG. 2  illustrates in more detail an illuminator according to a particular embodiment of the present invention; 
         FIG. 3  illustrates a substrate for a white phosphor according to a particular embodiment of the present invention; 
         FIGS. 4A and 4B  illustrate optical elements used to direct light around an opaque conductive material according to particular embodiments of the present invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present invention are illustrated in the Figures, like numerals being used to refer to like and corresponding parts of the various drawings. 
       FIG. 1  illustrates the anatomy of the eye into which the improved design for ocular implant provided by the present invention may be placed. Eye  100  includes cornea  102 , iris  104 , pupil  106 , lens  108 , lens capsule  110 , zonules, ciliary body  120 , sclera  112 , vitreous gel  114 , retina  116 , macula, and optic nerve  120 . Cornea  102  is a clear, dome-shaped structure on the surface of the eye acts as a window, letting light into the eye. Iris  104  is the colored part of the eye, called the iris, is a muscle surrounding the pupil that relaxes and contracts to control the amount of light entering the eye. Pupil  106  is the round, central opening of the iris. Lens  108  is the structure inside the eye that helps to focus light on the retina. Lens capsule  110  is an elastic bag that envelops the lens, helping to control lens shape when the eye focuses on objects at different distances. Zonules are slender ligaments that attach the lens capsule to the inside of the eye, holding the lens in place. The ciliary body is the muscular area attached to the lens that contracts and relaxes to control the size of the lens for focusing. Sclera  112  is the tough, outermost layer of the eye that maintains the shape of the eye. Vitreous gel  114  is the large, gel-filled section that is located towards the back of the eyeball, and which helps to maintain the curvature of the eye. Retina  116  is a light-sensitive nerve layer in the back of the eye that receives light and converts it into signals to send to the brain. The macula is the area in the back of the eye that contains receptors for seeing fine detail. Optic nerve  118  connects and transmits signals from the eye to the brain. 
     Ciliary body  122  lies just behind the iris  104 . Attached to the ciliary body  122  are tiny fiber “guide wires” called zonules  124 . Lens  108  is suspended inside the eye by the zonular fibers  124 . Nourishment for the ciliary body  122  comes from blood vessels which also supply the iris  104 . One function of ciliary body  122  is to control accommodation by changing the shape of the lens  108 . When the ciliary body  122  contracts, the zonules  124  relax. This allows the lens  108  to thicken, increasing the eye&#39;s ability to focus up close. When looking at a distant object, ciliary body  122  relaxes, causing the zonules  124  to contract. The lens  108  then becomes thinner, adjusting the eye&#39;s focus for distance vision. 
       FIG. 1  also shows a cross sectional view of an ophthalmic endoilluminator  200 , which may be an endoilluminator according to various embodiments of the present invention, located in an eye.  FIG. 1  depicts illuminator  200  coupled by an optical fiber to a handpiece  202  with probe  204  in use. Probe  204  is inserted into eye  100  through an incision in the pars plana region. Probe  204  illuminates the inside or vitreous region  114  of eye  100 . In this configuration, probe  204  can be used to illuminate the inside or vitreous region  114  during vitreo-retinal surgery. 
     Ophthalmic endoilluminators have been previously based either on halogen tungsten lamps or high pressure arc lamps (metal-halides, Xe). The advantages of arc lamps are small emitting area (&lt;1 mm), color temperature close to daylight, and longer life than in halogen lamps—400 hours vs. 50 hours. The disadvantage of arc lamps is high cost, decline in power, complexity of the systems and the need to exchange lamps several times over the life of the system. 
     LED based illuminators may provide considerably lower cost and complexity, and characteristic life times of 50,000 to 100,000 hours that would allow operating ophthalmic fiber illuminator for entire life of the instrument with very little drop in output and without a need of exchanging LEDs. A typical white LED may include a short-wavelength (ultra violet (UV)/violet/blue) LED exciting a white phosphor cap that emits white light, the source of light exciting the white phosphor layer being referred to as a “pump light source.” One limit to the output brightness of the white LED is that the quantum efficiency of the white phosphor, i.e., the number of photons emitted per photon incident on the phosphor material, depends on the temperature of the phosphor material. Specifically, as the temperature of the phosphor material increases, the quantum efficiency decreases. One significant drawback of existing systems is that the short-wavelength LED must operate at a relatively high temperature in order to produce sufficiently bright short-wavelength light for an adequate output brightness of the white phosphor. But this in turn limits the efficiency of the white phosphor layer. 
     Unlike conventional illuminators, various embodiments of the present invention thermally isolate the white phosphor from the short-wavelength LED. For purposes of this specification, “white phosphor” refers not only to broad band white phosphor materials but also to wavelength converting materials that either combine with light from the pump light source or combine light of different colors from multiple materials to produce bright light in a relatively broad region of the visible spectrum. For purposes of this specification, “thermally isolated” means that heat from the pump light source is either prevented from conducting directly to the white phosphor layer by the use of intervening insulators, heat sinks, air gaps, or other techniques known in the art or conducted away in a sufficient amount that the temperature of the white phosphor layer is primarily determined by the equilibrium temperature of another structure than the pump light source. Because the white phosphor is thermally isolated from the short-wavelength pump light source, the quantum efficiency of the white phosphor can be preserved even when the short-wavelength pump light source operates at a relatively high efficiency. While conventional illuminators would suggest that the intimate contact of the short-wavelength LED to the white phosphor is necessary for adequate incidence of short-wavelength light on the white phosphor, various embodiments of the present invention have demonstrated that allowing thermal isolation between the short-wavelength LED and the white phosphor can allow for sufficiently increased quantum efficiency to produce greater brightness even given the additional complications involved in thermally isolating the components. 
       FIG. 2  illustrates a particular embodiment of the illuminator  200  in greater detail. In the illustrated embodiment, illuminator  200  includes a pump light source  206  separated from a white phosphor  208  by a light collector  210 . The pump light source  206  and white phosphor  208  are held at a distance from one another by thermally insulating mounts  212 , so that the pump light source  206  and white phosphor  208  are thermally isolated from one another. The light collector  210  helps to compensate for the increased separation by collecting light emitted by the pump light source  206  and directing it onto the white phosphor  208 . 
     The white phosphor  208  is mounted on a substrate  214  of material transparent to the short-wavelength light of the pump light source  206 . A base of the substrate  214  is connected to the thermally insulating mount  212  by a thermoelectric cooler  216  and a cooling plate  218 . The cooling plate  218  provides additional mass to take up heat that can be conducted, convected, or radiated away, which may advantageously be formed from a thermally conductive material such as a metal. The thermoelectric cooler  216  is an electrical heat pump that is commonly used as an active cooling device for semiconductors and in this case is used to remove heat from the white phosphor  208 . Although the specific example of a thermoelectric cooler  216  is illustrated, it should be understood that any sort of active or passive cooling device suitable for use in relatively small spaces could be used, including liquid or air cooling systems. More generally, any type of “heat sink,” referring to any combination of elements or materials that actively or passively remove sufficient heat from the white phosphor  208  so as to primarily determine the temperature of the white phosphor  208  as compared to the pump light source  206 , may be employed to assist in thermally isolating the white phosphor  208   
       FIG. 3  illustrates a particular embodiment of the present invention using a substrate  214  that includes a thermally conductive material  220 . The conductive material  220  may be any suitable material with a higher thermal conductivity than the substrate  214 , including but not limited to metals such as copper or carbon nanotubes. Liquid and/or thermoelectric cooling may also be used in conjunction with conductive material  220 . In the depicted embodiment, the conductive material  220  is formed into a grid covering an area substantially equal to the area of a back surface of the white phosphor  208  facing the substrate  214 . This advantageously increases the thermal contact area with the white phosphor  208  in order to provide more efficient cooling. 
     In principle, conductive material  220  may be transparent to short-wavelength light from the pump light source  206 , but many materials that are desirable in terms of having a high thermal conductivity are opaque. The use of such materials can cause loss of light incident on the white phosphor  208  due to shadowing of the white phosphor  208  by the opaque conductive material  220 .  FIGS. 4A and 4B  illustrate embodiments of the substrate  214  that can help to prevent light loss from absorption by the opaque conductive material  220 . In  FIG. 4A , the substrate  214  includes a plurality of lenses  222  having planar back surfaces. The planar back surfaces of the lenses  222  extend across the back surface of the substrate  214  so as to allow light to be collected across substantially the entire back surface. The lenses  222  then focus the light into gaps between the conductive material  220 , so that light hitting the back surface of the substrate  214  does not hit the conductive material  220 .  FIG. 4B  illustrates a similar configuration of the substrate  214  in which lenses  224  are placed between conductive material  220 . In  FIG. 4B , the conductive material  220  has a wider cross-sectional area near the white phosphor  208  to improve the thermal contact area and to make cooling of the white phosphor  208  more efficient. Conversely, the lenses  224  have a wider cross-sectional area facing the pump light source  206  at the back surface of the substrate  214 , allowing light to be collected over a wider area and to be directed between gaps in the conductive material  220 . 
     The present invention is illustrated herein by example, and various modifications may be made by a person of ordinary skill in the art. Although the present invention is described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the scope of the invention as claimed.