US 3893447 A
Simultaneous angiography of the separate retinal and choroidal circulations of the human eye is accomplished following a single intravenous injection of a mixture of at least two dyes having differing spectral characteristics. In a preferred embodiment of the invention, a single injection of a mixture of sodium fluorescein and indocyanine green dyes is administered intravenously to the subject. Angiograms of the separate retinal and choroidal circulations are then taken simultaneously with a fundus camera modified to separate the electromagnetic radiation emanating from the eye which is respectively attributable to the sodium fluorescein dye and to the indocyanine green dye.
Description (OCR text may contain errors)
United States Patent 1 Hochheimer et al.
[451 July 8,1975
[ SIMULTANEOUS ANGIOGRAPHY OF THE SEPARATE RETINAL AND CHOROIDAL CIRCULATIONS  Inventors: Bernard F. l-Iochheimer, Lineboro;
Robert W. Flower, Timonium, both [2|] Appl. No.: 366,408
 US. Cl. 128/2 A; 128/2 T; l28/303.l; 351/9; 356/51  Int. Cl. A6IB 5/00  Field of Search 128/2 A, 2 T, 303.1; 351/9; 356/51  References Cited UNITED STATES PATENTS 3,313,290 4/l967 Chance et l28/2 A 3,327,l l9 6/l967 Kamentsky l28/2 A 3,461,856 8/l969 Polanyi 128/2 L 3,497,690 2/1970 Wheeless, Jr. et a1 356/5l X 3,542,457 1 H1970 Balding et al 351/9 X OTHER PUBLICATIONS Hochheimer, B. F., Arch. Opthal, Vol. 86, Nov. 1971,
Kogure et al., Arch. Opthal., Vol. 83, Feb. I970, pp. 209-2l4.
McCready, V. R. et al., Brit. Journ. of Radiology, Vol. 44, Nov. [971, pp. 870-877.
Primary Examiner-Kyle L. Howell Attorney, Agent, or FirmRobert E. Archibald; Kenneth E. Darnell [5 7] ABSTRACT Simultaneous angiography of the separate retinal and choroidal circulations of the human eye is accomplished following a single intravenous injection of a mixture of at least two dyes having differing spectral characteristics. In a preferred embodiment of the invention, a single injection of a mixture of sodium fluorescein and indocyanine green dyes is administered intravenously to the subject. Angiograms of the separate retinal and choroidal circulations are then taken simultaneously with a fundus camera modified to separate the electromagnetic radiation emanating from the eye which is respectively attributable to the sodium fluorescein dye and to the indocyanine green dye.
11 Claims, 2 Drawing Figures PMFF-FTFHJUL R 7 SHEET SIMULTANEOUS ANGIOGRAPHY OF THE SEPARATE RETINAL AND CHOROIDAL CIRCULATIONS STATEMENT OF GOVERNMENT INTEREST The invention herein described was made in the course of work under a grant or award from the Department of Health, Education, and Welfare.
BACKGROUND OF THE INVENTION 1. Field of the Invention The invention generally relates to angiography of the human ocular circulations, thereby providing diagnostic information useful in the treatment of a variety of disorders of the eye, such as glaucoma, choroidal melenoma, etc.
2. Description of the Prior Art Previous information concerning the dynamics of the retinal and choroidal circulations of the eye was derived to a large degree from fluorescein angiographic studies. The spectral characteristics of sodium fluorescein dye, the substance injected into the body in the practice of fluorescein angiography, make this angiographic technique effective as a routine clinical tool only for the study of normal and pathological human retinal circulations. Except for the very earliest choroidal arterial filling, visualization of the choroidal circulation is limited by the spectral characteristics of eye pigments and tissue which inefficiently transmit the excitation and emission energies of fluorescein and by the rapid extravasation of fluorescein from the choriocapillaris.
Even with the ability now available to the practitioner of viewing the ocular circulations through the separate use of sodium fluorescein and indocyanine green dyes, confusion and inaccuracy characterized attempts to evaluate angiograms produced in the infrared. Conflicting reports and statements concerning the basic understanding of the effects and mechanics of induced ocular hypertension further confused the situation and produced controversy over which of the two circulatory systems closes at the higher critical pressure. One major reason for the confusion has been defined by us to be the inability to evaluate both the retinal and choroidal circulations simultaneously. The solution to this problem is embodied in the present invention. In a first instance, the simultaneous practice of both retinal and choroidal angiography allows evaluation of the less well-understood choroidal circulation in light of the better understood retinal circulation which has been viewed simultaneously, thereby resulting in the ability to more quickly and efficiently raise the level of infrared angiographic evaluation of the choroidal circulation to a precise science. In this sense, the comparison of angiograms taken of the retinal circulation with sodium fluorscein in the visible spectrum with angiograms taken of the choroidal circulation with indocyanine green in the infrared allows a determination of the particular choroidal blood dynamics which prove to be most beneficial for differentiating normal and abnormal circulation patterns. In a second instance, the ability to view the ocular circulations simultaneously has produced modification of the manner in which wellknown fluorscein angiograms are evaluated. In the treatment of ocular disorders such as glaucoma wherein hypertension is induced in the eye, the present invention allows visualization of the respective filling characteristics of the two circulations simultaneously, thereby providing significantly more valuable information for diagnostic evaluation than would be available from the separate visualizations of the retinal and choroidal circulations.
SUMMARY OF THE INVENTION The invention generally comprises intravenous injection of a dye mixture into the body and the simultaneous recordation of the passage of the respective dyes through the ocular vasculatures with at least two cameras. The dyes employed in the mixture are chosen for their varying spectral characteristics, one of the dyes being chosen for its ability to emit or absorb electromagnetic radiation in one region of the spectrum and a second dye being chosen for its ability to emit or absorb electromagnetic radiation in a different region of the spectrum. Two such dyes are sodium fluorescein and indocyanine green which are additionally desirable due to their proven safe use in the human body. Through use of this dye composition of matter, an angiogram in the visible portion of the spectrum can be produced of the retinal circulation and one or more angiograms in the infrared can be produced of the choroidal circulation, the angiograms being related due to having been produced simultaneously.
The angiograms of the separate circulations are simultaneously produced by at least two cameras mounted on a fundus camera equipped with an optical separation device. The optical separation device splits the light energy returning from the ocular fundus during each flash tube firing into two or more separate beams, one of said beams corresponding to the spectral range of sodium fluorescein dye fluorescence in the retinal circulation and a second beam corresponding to the spectral range of the indocyanine green absorption band in the choroidal circulation. The presence of each of the two dyes is thus detected by different cameras.
Accordingly, it is a primary object of the invention to simultaneously view the separate retinal and choroidal circulations.
It is also an object of the invention to produce angiograms of the separate retinal and choroidal circulations simultaneously.
Further objects and advantages of the invention will become more apparent from the following detailed description of the preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic illustrating a fundus camera fitted with an optical splitter and two separate recordation cameras for respectively photographing the emission spectra of sodium fluorescein and the absorption spectra of indocyanine green; and,
FIG. 2 is a schematic illustrating a fundus camera fitted with two optical splitting devices and three separate recordation cameras for respectively photographing the emission spectra of both soduim fluorescein and indocyanine green and the absorption spectra of indocyanine green.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The separate choroidal and retinal circulations may be separately photographed due both to the distinct anatomical differences between the two vasculatures and to differing spectral characteristics of indocyanine green and sodium fluorescein dyes. The anatomical differences present conditions in the choroid which are suitable for photographing indocyanine green dye but are detrimental for photographing sodium fluorescein. In the retina, the situation is reversed. Any dye combination having the same or similar dye characteristics could also be used to practice the invention.
The characteristics of the eye and of the dye itself which cause sodium fluorescein to be useful in retinal angiography are:
I. the absorption and emission spectra of sodium fluorescein are in the visible portion of the spectrum, i.e., near 490 nm and 520 nm, respectively;
2. the pigment epithelium and macular xanthophyll which overlie the choroid inefficiently transmit visible light energy up to 700 nm;
3. although fluorscein is a fluorsecent dye of high quantum efficiency fluorescence occurs most efficiently in a thin surface layer due to the ability of hemoglobin in blood to efficiently absorb the excitation and emission energies affecting fluorescein molecules in deeper layers; and,
4. sodium fluorescein dye is about 40% unbound to blood protein constituents but does not leak" from normal blood vessels in the retina due to the tight normally endothealial cell junctions of the vessel walls.
These same characteristics are responsible for the ineffectiveness of sodium fluorescein in choroidal angiography. Increased distance of travel through a solvent attenuates the intensity of both excitation and emitted light energies in the deeper layers thereof; light energy emitted from sodium fluorescein deep in a solution being reabsorbed before reaching the surface of the solution. In this fashion the presence of sodium fluorescein in the retinal circulation reduces the amount of fluorescein fluorescence in the choroidal circulation and ability to be transmitted to the recording media. indocyanine green dye has its absorption spectrum in the near infrared portion of the spectrum, i.e., near 800 nm, where the pigment epithelium and macular xanthophyll are relatively transparent. When infrared light is used, the absorption of energy by indocyanine green dye is detectable in both the retinal and choroidal circulations. However, the greater volume of indocyanine green dye in the choroidal circulation has a greater absorptive capacity than the lesser retinal volume, thereby resulting in the visualization of only the major retinal vessels superimposed on the choroidal vasculature in infrared absorption angiograms.
In general absorption angiography differs from fluorescent angiography in that the latter involves a reemission process following absorption of the incident light energy. A small body, such as a capillary, can be photographed even though it is below the resolution limits of the optical system in use if the body is selfluminous, as in fluorescent angiography. In absorption angiography, the resolution limit is determined by the characteristics of the entire optical system, including the eye, camera, and film.
It can be demonstrated that for equal amounts of input light to the retina, approximately four times the amount of light energy is absorbed in the spectral range of sodium fluorescence (-500nm) than in the spectral range of indocyanine green (-800nrn),. In addition, upon reaching the pigment epithelium and choroid, approximately twice the amount of light energy is absorbed in the spectral range of sodium fluorescein than in the range of indocyanine green. Consequently, for choroidal angiography, infrared energy is more efficient than visible light energy. Considering the separate requirements of the two dyes primarily used herein, a differing choice of dyes or other substances may be employed as long as the relative spectral requirements are adhered to and the substances are safe for use in the human body.
Since sodium fluorescein absorption and emission spectra occur in not completely overlapping regions of the spectrum from indocyanine green absorption and emission spectra, the light energy characteristically reflected or absorbed from each of them may be optically detected in blood when the dyes are present simultaneously. Accordingly, the invention may be practiced by the intravenous injection into the body of a mixture of sodium fluorescein and indocyanine green, the two substances being chosen inter alia due to their long history of clinical application without harmful effects to human beings. The dye substances comprising the mixture are chemically inert. Mixing of the substance does not alter the physical or spectroscopic characteristics normally exhibited by either of the substances.
A typical injection of the aforementioned mixture consists of 20-40 mg. of indocyanine green dissolved in 2-3 ml of 10% sodium fluorscein, i.e., 200-300 mg of sodium fluorescein. The mixture is administered by rapid injection into the patient's cubital vein followed by a 5 ml normal saline flush. A rapid injection of a small bolus of the mixture maximizes the amount of that bolus which is directed to the head on the first pass through the arteries thereof through the heart. In lieu of the saline flush, the patient may be instructed to hold his breath for several seconds after the needle containing the mixture has been inserted into the vein. The breath is then expelled coincidentally with a slow count to four. On the count of two, the mixture is rapidly injected. In this fashion, venous blood flow away from the cubital vein injection site is slowed by elevated intrathoracic pressure, this condition tending to prevent the mixture from flowing rapidly from the injection site until the entire volume of the mixture has been introduced into the vein. At the count of four the patient inhales, producing a rapid drop in the intrathoracic pressure and thereby permitting the mixture in the vein to flow rapidly to the heart in as small a bolus as possible.
After injection of the mixture as described above, angiograms are produced using a fundus camera structured to provide at least two separate optical paths, the paths being provided for separately recording the respective retinal and choroidal circulations. Given the structure of the fundus camera as will be provided hereinafter, the separate angiograms are produced in a well-known fashion over an appropriate period of time. At least two sets of angiograms are simultaneously produced, one set recording the fluorescence of sodium flourescein, an indication of the filling of the retinal vasculature, while the second set of angiograms records absorption of indocyanine green, an indication of filling of the larger vessels of the choroidal circulation. A third set may also be produced which records the emission spectra of indocyanine green, an indication of the filling of the choroidal arteries and choriocapillaris.
These simultaneously produced sets of angiograms enable simultaneous observation of the two major ocular vaculatures responsible for maintenance of the sensory retina.
FIG. 1 is a diagrammatic view of a fundus camera structured to allow the production of two sets of angiograms as described above. The main body 12 of the camera 10 houses wellknown optical components typically used in prior art cameras of this type. One modification to structure within the main body 12 comprises the provision of a shutter 14 which acts to prevent light from focusing lamp 16 from reaching the eye 18 of a patient. An infrared absorbing filter 20 is placed between the lamp 16 and the shutter 14 to protect the shutter blades from heat damage. When a picture is taken, the shutter 14 is closed in a manner to be described. Otherwise, the shutter 14 is kept open for focusing purposes. A second modification involves disposition of a filter 22 in front of flash lamp 24. These modifications allow white" light to be used for focusing without interfering with the blue illuminating light needed for film exposure.
A practitioner using the camera It] focuses the camera through an eyepiece 26 and a movable mirror 28, the eyepiece 26 being rotated 90 in FIG. 1 (for ease of illustration). On achieving a desired focus, the practitioner activates a microswitch 30 which electrically closes the shutter 14, thus preventing light from the focusing lamp 16 from mixing with the light from the flash lamp 24. Activation of the microswitch 30 also causes movement of the mirror 28 from the optical path between the eye 18 and the photographic devices to be described hereinafter. On movement of the mirror 28 from the aforesaid optical path, a second microswitch 32 activates two motorized cameras 34 and 36 and causes the lamp 24 to flash, thereby initiating the photographic sequence.
The output of the flash lamp 24 is filtered by the filter 22 to remove electromagnetic energy in the wavelength range between 500 and 700 nm and also in the wavelength range above 800 nm. These wavelength ranges correspond respectively to the fluorescence bands of sodium fluorescein and indocyanine green. The electromagnetic energy passing through the filter 22 is directed by a well-known arrangement of optical components to the eye 18, a mirror 38 finally directing the energy to the eye. The mirror 38 has a hole 39 disposed therein which lies in the optical path existing between the eye 18 and the camera 36, the hole 39 being necessary to allow passage of light energy emanating from the eye 18 therethrough. Light thus emanating from the eye 18 and passing through the hole 39 in the mirror 38 is focused in a well-known fashion onto a filter 40 which transmits only the electromagnetic energy of wavelengths above 500 nm. The light energy thus transmitted through the filter 40 is focused on lens 42 which concentrates the light energy on a beam splitter 44. The lens 42 is disposed at a point at which the standard camera optics in the main body 12 forms a real image of the retina of the eye 18. The lens 42 is disposed in this image plane in order to relay an intermediate image of the iris of the eye 18 into the aperture stop of relay lenses lying in the respective optical paths leading to the cameras 34 and 36, thereby to prevent vignetting of the images in the film planes of the cameras 34 and 36. This light energy above 500 nm is split by the beam splitter 44 into two separate beams of electromagnetic energy. Electromagnetic energy of a wavelength range between 500 and 700 nm is reflected by the beam splitter 44 along an optical path leading to the camera 34. Electromagnetic energy of a wavelength range above 700 nm is transmitted through the beam splitter 44 along an optical path leading to the camera 36.
The light beam reflected along the optical path leading to the camera 34 is focused by a well-known arrangement of optical components onto a film strip 46 which is sensitive to visible light and is thus exposed within the camera 34 by the reflected light beam.
The light beam comprised of electromagnetic energy above 700 nm is filtered by a filter 48 to allow only a relatively narrow wavelength band around 800 nm to pass therethrough. The relatively narrow wavelength band of infrared energy passing the filter 48 is focused by well-known optical components onto an infraredsensitive film strip 50 in the camera 36, the film strip 50 being thus exposed by the infrared beam transmitted thereto.
The cameras 34 and 36 thus used to produce angiograms on the film strips 46 and 50 are standard, motordriven devices such as 35 nm Nikon cameras. Angiograms are taken at least every one-half second in order to adequately record the dynamic changes in the respective circulations. Battery and cable connections between the cameras 34 and 36 and the microswitch 32 are not shown for simplicity. The film strips 46 and 50 may comprise Kodak" Tri-X" film and Kodak" High-Speed Infrared film respectively. Development times and procedures are within the standard practices for the use of these films. The fluorescense of sodium fluorescein in the retinal circulation is recorded on the film strip 46 and the absorption of indocyanine green in the ehoroidal circulation provides the image resolution on the film strip 50. On the film strip 50, the areas of said film strip which receive the least exposure correspond to the areas of the fundus where light energy was absorbed by indocyanine green rather than being reflected back toward the camera 36. Therefore, the lightened film areas of the strip 36 correspond to the ehoroidal vessels.
Through the use of the apparatus thus described, simultaneous angiograms of the retinal and ehoroidal circulations are produced. The two circulations are separately pictured in the two angiograms thus produced but are produced on the same time scale, thereby providing the practitioner information not available from the separate practices of fluorscein and infrared absorption angiography.
FIG. 2 diagrammatically illustrates a second angiographic arrangement whereby three sets of angiograms of the separate retinal and ehoroidal circulations can be produced. A camera body such as 12 in FIG. 1 is employed to produce a beam of electromagnetic energy emanating from an eye of a patient. The beam of electromagnetic energy is split by beam splitter 52 into two component beams, a first beam of a wavelength range between 500 and 600 nm is transmitted through the beam splitter 52 and is recorded on a film strip 54 sensitive to visible light in camera 56. Electromagnetic energy of a wavelength above 700 nm is reflected by the beam splitter 52 to a second beam splitter 58. The beam splitter 58 transmits electromagnetic energy above 800 am through a filter 60 and to an image intensifier 61, the visible output of which is relayed to film strip 62 where the light energy is recorded in camera 64, the filter 60 acting to further filter out electromagnetic energy of a wavelength less than 800 nm. Electromagnetic energy of a wavelength below 800 nm is reflected by the beam splitter 58 to a bandpass filter 66 which passes only that energy having a wavelength of 790 nm. The energy transmitted through the filter 66 is recorded on a film strip 68 in a camera 70.
Three sets of angiograms are thus produced. The image recorded on the film strip 54 corresponds to the fluorescence of sodium fluorescein and essentially pictures the retinal circulation. The images recorded on the film strips 62 and 68 respectively corresponds to the fluorescence and absorption of indocyanine green. The angiogram produced by the absorption of indocyanine green provides information relating to the filling of the choroidal circulation, particularly the veins. The angiogram produced by the fluorescence of indocyanine green provides information relative to the filling of the choroidal arteries and capillaries of the choriocapillaries. Visualization of the choriocapillaries is possible in this fashion since indocyanine green does not rapidly extravasate from the choriocapillaris and since dye fluorescence is primarily a surface phenomenon.
The composition of matter employed in the practice of the invention is described as being a mixture of sodium fluorescein and indocyanine green. The mixture may be stabilized with serum albumin. As previously mentioned, these two substances are preferred due to their spectral characteristics and due to the ability to safely use these substances in the human body. It is to be understood that sodium fluorescein could be replaced by any substance exhibiting fluorescence in the visible portion of the spectrum, particularly between 500 to 600 nm, and which is safe for use in the human body. Similarly, indocyanine green could be replaced in the mixture by any substance exhibiting absorption in the near infrared, particularly around 800 nm, and which is safe for use in the human body. Any replacement in the mixture for indocyanine green would prove more valuable if it also exhibited fluorescence in the infrared portion of the spectrum above 800 nm. Any dye combination having separable characteristics, even if the spectral characteristics overlap, could be employed in the practice of the invention.
It is understood that the invention may be practiced, other than as specifically described hereinabove, the invention being limited as recited in the following claims.
What is claimed is:
l. A method for the simultaneous angiography of the separate retinal and choroidal circulations of the eye, comprising the steps of:
injecting a mixture of substances into the circulatory blood system of the human body, the substances of the mixture transmitting electromagnetic radiation in different portions of the electromagnetic spectrum;
irradiating the eye with electromagnetic radiation;
splitting the electromagnetic radiation transmitted from the eye into at least two components having different wavelength ranges; and,
recording the separate radiation components independently of each other.
2. The method of claim 1 wherein the mixture of substances comprises a first substance which transmits electromagnetic radiation in the visible portion of the spectrum on irradiation thereof and a second substance which transmits electromagnetic radiation in the infrared portion of the spectrum on irradiation thereof.
3. The method of claim 1 wherein the mixture of substances comprises sodium fluorescein dye and indocyanine green dye.
4. The method of claim 3 wherein the electromagnetic radiation transmitted from the eye is split into a first component in the visible portion of the spectrum which corresponds to the emission spectra of sodium fluorescein dye and a second component in the infrared portion of the spectrum which corresponds to the absorption spectra of indocyanine green dye.
5. The method of claim 4 wherein said first component is recorded at predetermined temporal intervals by a first camera using film sensitive to visible radiation for recording the filling of the retinal circulation of the eye and wherein said second component is simultaneously recorded at the same temporal intervals by a second camera using film sensitive to infrared radiation for recording the filling of the choroidal circulation of the eye.
6. The method of claim 4 wherein the electromagnetic radiation transmitted from the eye is further split into a third component in the infrared portion of the spectrum which corresponds to the emission spectra of indocyanine green dye.
7. The method of claim 6 wherein said first component is recorded at predetermined temporal intervals by a first camera using film sensitive to visible radiation for recording the filling of the retinal circulation of the eye, wherein said second component is simultaneously recorded at the same temporal intervals by a second camera using film sensitive to infrared radiation for recording the filling of the larger vessels of the choroidal circulation of the eye, and wherein said third component is simultaneously recorded at the same temporal intervals by a third camera using film sensitive to infrared radiation for recording the smaller vessels of the choroidal circulation of the eye.
8. Apparatus for simultaneously producing angiograms of the separate retinal and choroidal circulations of the eye, comprising:
flash means for irradiating the eye with electromagnetic radiation,
filter means for removing electromagnetic radiation in the wavelength ranges of 500 to 700nm and above 800nm respectively prior to entry of said radiation in to the eye;
beam splitting means for separating the electromagnetic radiation emanating from the eye after irradiation thereof into at least two components having different wavelength ranges; and,
means for separately recording said components.
9. The apparatus of claim 8 and further comprising means for separating the electromagnetic radiation in the wavelength range above 500 nm emanating from the eye into two separate components having respective wavelength ranges of between 500 to 700 nm and above 700 nm.
10. The apparatus of claim 9 and further comprising filter means for removing electromagnetic radiation from the component lying in the wavelength range above 700 nm all radiation except that radiation in a narrow band around 800 nm.
11. Apparatus for simultaneously producing angiograms of the separate retinal and choroidal circulations of the eye, comprising:
9 l flash means for irradiating the eye with electromaga first component having a wavelength range be- H m radiation; tween 500 to 600nm and a second component havbeam splitting means for separating the electromagm a wavelength range above 700mm and a Second netic radiation emanating from the eye after irradiation thereof into components having different wavelength ranges, the beam splitting means component beams of wavelengths greater than and prising at least two optical separation devices, a less than 800m" respectvelyi and first device separating the electromagnetic radiameans for p recording said componentstion emanating from the eye into two components,
device separating said second component into