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The Effect of High Intensity Light on Choroidal Circulation*
REFINEMENT IN CATARACT SURGERY
277
8. Lindner, K.: U e b e r Abänderungen der intrakapsularen Staroperation. Ber. deutsch, ophth. G e s e l l s c h , 52:392-400, 1938. 9. M c L e a n , J. M . : A n e w corneoscleral suture. A r c h . O p h t h , 2 3 : 5 5 4 - 5 5 9 , 1940. 10. Roper, K. L . : Suturing in cataract surgery. T r . A m . Ophth. S o c , 52:587-749, 1954. 11. Roberts, W . : Buried sutures for closure o f cataract incision. A m . J. O p h t h , 3 5 : 1 4 5 9 - 1 4 6 3 , 1952. 12. Scheie, H . G.: Incision and closure in cataract extraction. A r c h . O p h t h , 6 1 : 4 3 1 - 4 5 2 , 1959.
THE
EFFECT
OF
HIGH
CHOROIDAL WALTER
J.
GEERAETS,
M.D.,
DUPONT
MRINMAY
GUERRY,
Richmond,
The increasing use of high intensity radiant energy for treatment of ocular diseases requires a more thorough investigation of both immediate and late tissue effects. It has been stressed repeatedly that heavy coagulations result in severe destructive lesions of the retina and choroid and can even produce explosionlike rupture of these structures. This is true particularly when high intensities are delivered in a short period of time. Because of such extensive destruction it has been emphasized to perform coagulations with lowest intensities leading to the desired tissue response. 1
Contrary to this, it has been suggested that deliminating barrages with greater intensities should be employed prior to lightcoagulation treatment of retinal or chorioretinal malignancies, supposedly because such barrages isolate the tumor from its blood supply, thus blocking nourishment and oxygenation of the lesion and at the same time preventing hematogenous metastasis of tumor cells. In the following experiment the effectiveness of such encircling barrages has been evaluated and applied energy measured. 2
METHOD
One hundred and two chinchilla gray rabbits were used in this study.' Animals with the same degree of fundus pigmenta* From Research Virginia. American
INTENSITY
LIGHT
ON
CIRCULATION*
the Department of O p h t h a l m o l o g y and Ophthalmology, T h e Medical College o f T h i s study w a s supported in part by the Cancer Society.
III,
GHOSH,
M.D.,
AND
M.D.
Virginia
tion were selected in order to have a uniform baseline for better comparison. Uniformity of pigmentation was determined by fundus reflex measurements. The pupils were dilated maximally with atropine (one percent) and Neosynephrine ( 1 0 percent). All experiments were carried out under general anesthesia with intravenous Nembutal. Retinal doses, measured in cal./cm. for the total given exposure time, were changed by varying the exposure time only, leaving the retinal irradiance ( Q ) , defined as cal./ cm. per unit time, unaltered. The calibrated retinal irradiance at the lowest intensity of the lightcoagulator (selector switch on "green" and multistage switch on 1 and image field diaphragm setting of 4.5 degrees) measures 40.1 cal./cm. /sec. for the rabbit eye, uncorrected for absorption by ocular media. Total absorption within a spectral range from 350 to 1500 πιμ for the rabbit ocular media measures approximately 38 percent for uniform intensity and about 11 percent for the light emitted by the Xenon high pressure lamp X B O 2001 as employed in the Zeiss light coagulator." With exposure times of 0.1, 0.2, and 0.3 sec. the administered retinal doses amounted to 3.56, 7.12 and 10.68 cal./cm. , respectively. 2
r
2
2
2
A pilot study was performed to determine the effectiveness of both, single and double coagulation barrages. In the left eye of these animals a single ring of light coagulations was performed and in the right eye a double ring of coagulations, thus leaving a circular area of unexposed retina in the center of
278
W A L T E R J. G E E R A E T S , M R I N M A Y G H O S H A N D D U P O N T G U E R R Y , I I I
the barrage. The diameter of the encircling barrages measured approximately three disc diameters in size. Utmost care was taken to prevent gaps between the individual coagulation spots. In half of the experimental animals such barrages were placed in the posterior part of the globe and in the other half in the equatorial region. Immediately before death, a 20-gauge cannula was inserted into the lumen of the distal part of both carotid arteries and the proximal ends of the vessels were ligated. Both jugular veins were severed. The cranial vessels were first irrigated with normal saline, followed by injection of yellow latex paint of particle size smaller than 7μ. The latex paint was injected into both arteries until backflow through the jugular veins was noted. The distal parts of both arteries and veins were then ligated and the animals refrigerated for 24 hours to allow for intravascular hardening of the injected paint. After the results of the pilot study had been evaluated, only double barrages of light coagulations were used throughout the experiment since a single barrage proved inadequate. Animals were killed immediately after light coagulation and at different time intervals thereafter up to eight weeks after exposure. The enucleated globes were dissected as gross specimens under the dissecting microscope. The retina including the pigment epithelium was removed in toto. The choroidal vessels could then be clearly visualized and the obliterated vessels easily identified by means of the previously injected yellow paint. Two specimens for each time interval following light exposure were used for histologic examinations. RESULTS SINGLE
AND
DISCUSSION
BARRAGES
From the preliminary studies it became evident that in nine out of 10 eyes choroidal circulation could not effectively be blocked,
regardless of retinal dose or location of the experimental barrage. Choroidal vessels invariably remained open and passed into the encircled area between the coagulation spots, although the individual spots were placed as closely as possible to each other. For this reason no further experiments were performed with single light coagulation barrages. DOUBLE
BARRAGES
For all experiments where a double barrage was employed it can generally be stated, that, if a gap is left between neighboring coagulations of either outer or inner circle of the barrage, choroidal vessels will inevitably pass the barrage in that particular area (fig. 1 ) . Moreover, if the barrages are located in the posterior pole of the globe where short ciliary arteries penetrate the sclera (fig. 2 ) and such a vessel enters the choroid within the encircling barrage, blockage of choroidal blood supply to that area is not possible regardless of the applied light intensity (fig. 3 ) . Except for this last factor of short ciliary arteries, there appears to be no significant difference in the coagulation effect of identical retinal doses at either the posterior pole or the peripheral portion of the globe. While this holds true for most rabbit eyes it is not valid in the case of the human eye. With increasing obliquity of the entering light beam, there is a proportional increase in astigmatism which prevents sharp focusing of the light image on the retina. In the relatively uniformly pigmented human fundus, therefore, an increase in light intensity is necessary in order to bring about tissue response similar to that obtained in the posterior part of the fundus. Furthermore, the pupil opening of the patient's eye is ovalshaped for obliquely entering light and there is a rather marked decrease in the lightbeam diameter. For the human eye the intensity must therefore be increased by a factor of two, if the angle of incidence measures approximately 70 degrees.
EFFECT OF LIGHT ON CHOROIDAL CIRCULATION
279
F i g . 1 (Geeraets, Ghosh and G u e r r y ) . Circle of double light coagulation barrage. N o t e the choroidal vessel passing the barrage in an area w h e r e a g a p w a s left between t w o neighboring coagulation spots.
F i g . 2 (Geeraets, Ghosh and G u e r r y ) . E n t r a n c e of short ciliary vessels in the rabbit eye.
280
W A L T E R J. G E E R A E T S , M R I N M A Y G H O S H A N D D U P O N T G U E R R Y , I I I
F i g . 3 (Geeraets, Ghosh and G u e r r y ) . Short ciliary vessel entering the choroidal space within the area surrounded by double light coagulation barrage.
In the rabbit fundus on the other hand, pigmentation is usually much heavier in the periphery which makes for greater light absorption. The reduction of pupillary opening with increased obliquity of the incident light is less than in the human eye because of the different anatomy. These two factors compensate for the astigmatic error, which, in the rabbit eye is, however, not so pronounced as in the human eye. When these factors are considered, it becomes apparent that for identical corneal irradiances a similar tissue response can usually be obtained in posterior and peripheral parts of the rabbit fundus but not in the human eye. The three different exposure times (0.1, 0.2, and 0.3 sec.) used in this study were selected for two reasons. First, they correspond roughly to exposure times most frequently used in the clinical application of light coagulation where the manual release mechanism of the light coagulator handle is employed; and secondly, a decrease in ex-
posure time below 100 millisec. becomes increasingly inaccurate in spite of preset timing and electronic time recording with a digital counter. This is due to the lack of uniformity in opening and closing intervals of the mechanical semiphore shutter of the light coagulator which measure approximately 20 millisec. for each of these procedures. Hence, these irregular time intervals at the beginning and end of each exposure, are identical with the times to reach 90 percent of maximum irradiance and decay to 10 percent of maximum irradiance, respectively, and introduce too great a percentage of error in calculations of retinal irradiances if exposure times in millisec. ranges are used. With retinal doses of 3.56 cal./cm. (multistage switch "Green 1" or 49 amps, image field diaphragm 4.5 degrees, iris intensity diaphragm 0, exposure time 0.1 sec.) and complete double barrage of light coagulations, only 50 percent of the exposed eyes 2
EFFECT OF LIGHT ON CHOROIDAL
showed complete blockage of choroidal blood circulation within the encircled fundus area immediately after light exposure. In the other 50 percent, several choroidal vessels remained open and allowed blood to pass the coagulation barrage. In order to perform coagulations of the same degree on the human eye with the same retinal doses, leaving exposure time, iris diaphragm and image field diaphragm setting unchanged, the multistage switch would have to be set at the highest reading on the multistage switch for overload (Red I V ) , which corresponds to an arc current flow of 112 amps. With this setting the image size of the light beam at the retina would be larger in the human eye compared with that of the rabbit because of the different focal lengths. In the former it would measure about 1.28 mm. and in the latter 0.75 mm. in diameter. Decreasing the image field diaphragm to three degrees, which corresponds to a retinal image size of 0.88 mm. in the human eye, would, however, not alter the retinal irradiance substantially, providing the image of the electrodes are adjusted properly to remain within the field of light exposure. Experimental eyes, injected with latex paint and enucleated one day after light coagulation showed the same percentage of total blockage of choroidal blood flow within the encircled area as did those eyes examined immediately after coagulation. In the period from three days up to nine days after exposure, the percentage of eyes with completely obliterated blood circulation decreased and on the 10th day in all of the experimental eyes blood flow was re-established, although to a different degree (table 1). Increase of retinal dose to 7.12 cal./cm. by means of increasing exposure time to 0.2 s e c , but leaving all other instrument settings unchanged, resulted in a somewhat higher percentage of total choroidal vascular occlusion within the area encircled by the double light coagulation barrages. Blood 2
CIRCULATION TABLE
281
1*
A N A L Y S I S OF FINDINGS
D a y s after Light Coagulation
Total Number of E y e s
N u m b e r of E y e s with Vessels Not Blocked Blocked
Exposure Time Retinal D o s e 0 10 1 10 3 10 7 10 10 10
0 . 1 sec. 3.56 cal./cm. 5 5 3 2 0
Exposure Time Retinal D o s e 0 10 3 10 7 10 10 10 14 10
0 . 2 sec. 7.12 cal./cm.* 10 8 8 1 1
Exposure Time Retinal D o s e 0 6 1 6 3 10 7 20 8 10 10 10 12 10 14 10 21 10 28 6 42 4 56 2
s
5 5 7 8 10
0 2 2 9 9
0 . 3 sec. 1 0 . 6 8 cal./cm.» 6 0 6 0 10 0 20 0 8 2 7 3 5 5 10 0 1 9 0 6 4 0 0 2
* Distribution of light-coagulated rabbit e y e s within different groups according t o applied energy. C o l u m n 3 indicates the number of e y e s in which blood circulation is c o m p l e t e l y blocked after various t i m e intervals postcoagulation. C o l u m n 4 g i v e s the n u m b e r of e y e s in which blood circulation w a s not c o m p l e t e l y blocked or has restarted, respectively.
flow was blocked in all experimental eyes immediately after exposure. Three days after light coagulation circulation was restored in 20 percent of the eyes and 10 days after light exposure blood flow had returned in 90 percent of the eyes (table 1). A further increase in retinal dose to 10.68 cal./cm. , by increasing the exposure time to 0.3 s e c , should be regarded as the highest possible intensity that can be employed within that short an exposure time, since further energy increase would result in explosionlike disruption of choroid and retina. 2
282
W A L T E R J. G E E R A E T S , M R I N M A Y G H O S H A N D D U P O N T G U E R R Y ,
III
F i g . 4 (Geeraets, Ghosh and G u e r r y ) . Double light coagulation barrage which has effectively blocked any circulation to the encircled area. N o t e the choroidal rupture at the 11-o'clock position caused by too high intensity.
With such extremely high retinal doses complete blockage of choroidal blood flow was found to occur up to seven days after exposure (fig. 4 ) . From eight to 12 days postcoagulation, an increasing percentage of eyes showed different degrees of new blood circulation (fig. 5 ) . In all but one of the experimental eyes, blood flow had returned after 10 days. In one experimental eye no signs of active blood circulation could be observed 21 days after exposure (table 1 ) .
F i g . S (Geeraets, Ghosh and G u e r r y ) . N e w v e s sel formation within area encircled by heavy double light coagulation barrage 14 days previously.
A s already mentioned, even with such intense coagulation, vessels could be seen passing the light coagulation barrages if a gap was allowed to remain in the inner or outer circle of coagulations. A n interesting finding was that blood circulation peripheral to the barrages showed marked reaction with complete loss of function similar to that present in the central delimited zone. The duration of such changes was also comparable. The early return of blood flow to the area
EFFECT OF LIGHT ON CHOROIDAL
enclosed by coagulations of lower intensity is believed to be caused by reopening of spastic contractions of the vessel walls. Such contractions can be observed ophthalmoscopically when retinal vessels are coagulated. In such instances interruption of the blood column can be visualized but this occurs for only a limited period of time unless large doses are employed. The relatively long period for return of blood circulation after heavy intensities have been administered cannot be explained on the basis of spastic contraction alone. Recanalization and neovascularization take place and increase until adequate nutrition and oxygenation of the now atrophic chorioretinal scar is assured. Necrosis with complete hole formation or other complications, which one might expect following such heavy coagulations with inhibition of blood supply to such a large area, did not occur in any of the experimental eyes. CONCLUSION
From this study it can be concluded that single light coagulation barrages and those of only moderate intensity are ineffective in blocking blood supply to a fundus lesion. The therapeutic effect of such barrages can serve only in destroying peripheral tumor cells that might remain viable, if treatment were limited to the lesion alone. Isolation of such lesions can, however, be achieved, at least temporarily, by means of an extremely heavy double barrage. For clinical purposes such intensities are fraught with danger because of the probability of chorioretinal explosions, massive vitreous hemorrhages a n d / or retinal detachment secondary to hole formation. It might be argued, however, that in such instances a calculated risk may be worth the taking since the only alternative is enucleation. The decision to enucleate or to coagulate
CIRCULATION
283
remains that of the individual ophthalmologist, since no authoritative answer can be given until considerably greater clinical data have been accumulated and evaluated. SUMMARY
The effectiveness of light coagulation barrages on choroidal blood flow was studied in rabbit eyes. It was found that choroidal circulation can be completely blocked for a limited time, providing the following technique is followed. 1. A double line of light coagulation spots has to be employed with no gaping between individual coagulations. 2. Such double barrages must be located outside the fundus area where short ciliary vessels penetrate the sclera. 3. A retinal dose of at least 12 cal./cm. with a delivery time of 0.3 sec. had to be applied for complete chorioretinal vessel obliteration. This dose should be regarded as a maximal allowable intensity since with higher intensities explosionlike disruptions of retina and choroid might result. 4. Recanalization and neovascularization of the chorioretinal area surrounded by the double light coagulation barrage occurred from 10 to 14 days following light coagulation. 5. The clinical use of such an encircling double barrage with high intensities to delimit small malignant neoplasms of retina and choroid is hazardous and may lead to complications such as chorioretinal explosion, massive vitreous hemorrhage, and detachment. Barrages produced with lower energies will not be effective in interrupting the blood supply of the encircled lesion, but may be of value in destroying peripherally located tumor cells. 2
1200 East Broad Street
(19).
REFERENCES
1. Guerry, D . P . , I I I , W i e s i n g e r , H., Geeraets, W . J.: S y m p o s i u m o n lightcoagulation. Internat. Ophth. Clinics, v. I, no. 4, D e c , 1961. 2. M e y e r - S c h w i c k e r a t h , G.: L i g h t Coagulation. S t Louis, M o s b y , 1960. 3. Geeraets, W . J., W i l l i a m s , R. C , Chan, G., H a m , W . T., Guerry, D . , and Schmidt, F . : T h e loss o f light energy in retina and choroid. Α Μ Α A r c h . Ophth., 6 4 : 6 0 6 , 1960.
277
8. Lindner, K.: U e b e r Abänderungen der intrakapsularen Staroperation. Ber. deutsch, ophth. G e s e l l s c h , 52:392-400, 1938. 9. M c L e a n , J. M . : A n e w corneoscleral suture. A r c h . O p h t h , 2 3 : 5 5 4 - 5 5 9 , 1940. 10. Roper, K. L . : Suturing in cataract surgery. T r . A m . Ophth. S o c , 52:587-749, 1954. 11. Roberts, W . : Buried sutures for closure o f cataract incision. A m . J. O p h t h , 3 5 : 1 4 5 9 - 1 4 6 3 , 1952. 12. Scheie, H . G.: Incision and closure in cataract extraction. A r c h . O p h t h , 6 1 : 4 3 1 - 4 5 2 , 1959.
THE
EFFECT
OF
HIGH
CHOROIDAL WALTER
J.
GEERAETS,
M.D.,
DUPONT
MRINMAY
GUERRY,
Richmond,
The increasing use of high intensity radiant energy for treatment of ocular diseases requires a more thorough investigation of both immediate and late tissue effects. It has been stressed repeatedly that heavy coagulations result in severe destructive lesions of the retina and choroid and can even produce explosionlike rupture of these structures. This is true particularly when high intensities are delivered in a short period of time. Because of such extensive destruction it has been emphasized to perform coagulations with lowest intensities leading to the desired tissue response. 1
Contrary to this, it has been suggested that deliminating barrages with greater intensities should be employed prior to lightcoagulation treatment of retinal or chorioretinal malignancies, supposedly because such barrages isolate the tumor from its blood supply, thus blocking nourishment and oxygenation of the lesion and at the same time preventing hematogenous metastasis of tumor cells. In the following experiment the effectiveness of such encircling barrages has been evaluated and applied energy measured. 2
METHOD
One hundred and two chinchilla gray rabbits were used in this study.' Animals with the same degree of fundus pigmenta* From Research Virginia. American
INTENSITY
LIGHT
ON
CIRCULATION*
the Department of O p h t h a l m o l o g y and Ophthalmology, T h e Medical College o f T h i s study w a s supported in part by the Cancer Society.
III,
GHOSH,
M.D.,
AND
M.D.
Virginia
tion were selected in order to have a uniform baseline for better comparison. Uniformity of pigmentation was determined by fundus reflex measurements. The pupils were dilated maximally with atropine (one percent) and Neosynephrine ( 1 0 percent). All experiments were carried out under general anesthesia with intravenous Nembutal. Retinal doses, measured in cal./cm. for the total given exposure time, were changed by varying the exposure time only, leaving the retinal irradiance ( Q ) , defined as cal./ cm. per unit time, unaltered. The calibrated retinal irradiance at the lowest intensity of the lightcoagulator (selector switch on "green" and multistage switch on 1 and image field diaphragm setting of 4.5 degrees) measures 40.1 cal./cm. /sec. for the rabbit eye, uncorrected for absorption by ocular media. Total absorption within a spectral range from 350 to 1500 πιμ for the rabbit ocular media measures approximately 38 percent for uniform intensity and about 11 percent for the light emitted by the Xenon high pressure lamp X B O 2001 as employed in the Zeiss light coagulator." With exposure times of 0.1, 0.2, and 0.3 sec. the administered retinal doses amounted to 3.56, 7.12 and 10.68 cal./cm. , respectively. 2
r
2
2
2
A pilot study was performed to determine the effectiveness of both, single and double coagulation barrages. In the left eye of these animals a single ring of light coagulations was performed and in the right eye a double ring of coagulations, thus leaving a circular area of unexposed retina in the center of
278
W A L T E R J. G E E R A E T S , M R I N M A Y G H O S H A N D D U P O N T G U E R R Y , I I I
the barrage. The diameter of the encircling barrages measured approximately three disc diameters in size. Utmost care was taken to prevent gaps between the individual coagulation spots. In half of the experimental animals such barrages were placed in the posterior part of the globe and in the other half in the equatorial region. Immediately before death, a 20-gauge cannula was inserted into the lumen of the distal part of both carotid arteries and the proximal ends of the vessels were ligated. Both jugular veins were severed. The cranial vessels were first irrigated with normal saline, followed by injection of yellow latex paint of particle size smaller than 7μ. The latex paint was injected into both arteries until backflow through the jugular veins was noted. The distal parts of both arteries and veins were then ligated and the animals refrigerated for 24 hours to allow for intravascular hardening of the injected paint. After the results of the pilot study had been evaluated, only double barrages of light coagulations were used throughout the experiment since a single barrage proved inadequate. Animals were killed immediately after light coagulation and at different time intervals thereafter up to eight weeks after exposure. The enucleated globes were dissected as gross specimens under the dissecting microscope. The retina including the pigment epithelium was removed in toto. The choroidal vessels could then be clearly visualized and the obliterated vessels easily identified by means of the previously injected yellow paint. Two specimens for each time interval following light exposure were used for histologic examinations. RESULTS SINGLE
AND
DISCUSSION
BARRAGES
From the preliminary studies it became evident that in nine out of 10 eyes choroidal circulation could not effectively be blocked,
regardless of retinal dose or location of the experimental barrage. Choroidal vessels invariably remained open and passed into the encircled area between the coagulation spots, although the individual spots were placed as closely as possible to each other. For this reason no further experiments were performed with single light coagulation barrages. DOUBLE
BARRAGES
For all experiments where a double barrage was employed it can generally be stated, that, if a gap is left between neighboring coagulations of either outer or inner circle of the barrage, choroidal vessels will inevitably pass the barrage in that particular area (fig. 1 ) . Moreover, if the barrages are located in the posterior pole of the globe where short ciliary arteries penetrate the sclera (fig. 2 ) and such a vessel enters the choroid within the encircling barrage, blockage of choroidal blood supply to that area is not possible regardless of the applied light intensity (fig. 3 ) . Except for this last factor of short ciliary arteries, there appears to be no significant difference in the coagulation effect of identical retinal doses at either the posterior pole or the peripheral portion of the globe. While this holds true for most rabbit eyes it is not valid in the case of the human eye. With increasing obliquity of the entering light beam, there is a proportional increase in astigmatism which prevents sharp focusing of the light image on the retina. In the relatively uniformly pigmented human fundus, therefore, an increase in light intensity is necessary in order to bring about tissue response similar to that obtained in the posterior part of the fundus. Furthermore, the pupil opening of the patient's eye is ovalshaped for obliquely entering light and there is a rather marked decrease in the lightbeam diameter. For the human eye the intensity must therefore be increased by a factor of two, if the angle of incidence measures approximately 70 degrees.
EFFECT OF LIGHT ON CHOROIDAL CIRCULATION
279
F i g . 1 (Geeraets, Ghosh and G u e r r y ) . Circle of double light coagulation barrage. N o t e the choroidal vessel passing the barrage in an area w h e r e a g a p w a s left between t w o neighboring coagulation spots.
F i g . 2 (Geeraets, Ghosh and G u e r r y ) . E n t r a n c e of short ciliary vessels in the rabbit eye.
280
W A L T E R J. G E E R A E T S , M R I N M A Y G H O S H A N D D U P O N T G U E R R Y , I I I
F i g . 3 (Geeraets, Ghosh and G u e r r y ) . Short ciliary vessel entering the choroidal space within the area surrounded by double light coagulation barrage.
In the rabbit fundus on the other hand, pigmentation is usually much heavier in the periphery which makes for greater light absorption. The reduction of pupillary opening with increased obliquity of the incident light is less than in the human eye because of the different anatomy. These two factors compensate for the astigmatic error, which, in the rabbit eye is, however, not so pronounced as in the human eye. When these factors are considered, it becomes apparent that for identical corneal irradiances a similar tissue response can usually be obtained in posterior and peripheral parts of the rabbit fundus but not in the human eye. The three different exposure times (0.1, 0.2, and 0.3 sec.) used in this study were selected for two reasons. First, they correspond roughly to exposure times most frequently used in the clinical application of light coagulation where the manual release mechanism of the light coagulator handle is employed; and secondly, a decrease in ex-
posure time below 100 millisec. becomes increasingly inaccurate in spite of preset timing and electronic time recording with a digital counter. This is due to the lack of uniformity in opening and closing intervals of the mechanical semiphore shutter of the light coagulator which measure approximately 20 millisec. for each of these procedures. Hence, these irregular time intervals at the beginning and end of each exposure, are identical with the times to reach 90 percent of maximum irradiance and decay to 10 percent of maximum irradiance, respectively, and introduce too great a percentage of error in calculations of retinal irradiances if exposure times in millisec. ranges are used. With retinal doses of 3.56 cal./cm. (multistage switch "Green 1" or 49 amps, image field diaphragm 4.5 degrees, iris intensity diaphragm 0, exposure time 0.1 sec.) and complete double barrage of light coagulations, only 50 percent of the exposed eyes 2
EFFECT OF LIGHT ON CHOROIDAL
showed complete blockage of choroidal blood circulation within the encircled fundus area immediately after light exposure. In the other 50 percent, several choroidal vessels remained open and allowed blood to pass the coagulation barrage. In order to perform coagulations of the same degree on the human eye with the same retinal doses, leaving exposure time, iris diaphragm and image field diaphragm setting unchanged, the multistage switch would have to be set at the highest reading on the multistage switch for overload (Red I V ) , which corresponds to an arc current flow of 112 amps. With this setting the image size of the light beam at the retina would be larger in the human eye compared with that of the rabbit because of the different focal lengths. In the former it would measure about 1.28 mm. and in the latter 0.75 mm. in diameter. Decreasing the image field diaphragm to three degrees, which corresponds to a retinal image size of 0.88 mm. in the human eye, would, however, not alter the retinal irradiance substantially, providing the image of the electrodes are adjusted properly to remain within the field of light exposure. Experimental eyes, injected with latex paint and enucleated one day after light coagulation showed the same percentage of total blockage of choroidal blood flow within the encircled area as did those eyes examined immediately after coagulation. In the period from three days up to nine days after exposure, the percentage of eyes with completely obliterated blood circulation decreased and on the 10th day in all of the experimental eyes blood flow was re-established, although to a different degree (table 1). Increase of retinal dose to 7.12 cal./cm. by means of increasing exposure time to 0.2 s e c , but leaving all other instrument settings unchanged, resulted in a somewhat higher percentage of total choroidal vascular occlusion within the area encircled by the double light coagulation barrages. Blood 2
CIRCULATION TABLE
281
1*
A N A L Y S I S OF FINDINGS
D a y s after Light Coagulation
Total Number of E y e s
N u m b e r of E y e s with Vessels Not Blocked Blocked
Exposure Time Retinal D o s e 0 10 1 10 3 10 7 10 10 10
0 . 1 sec. 3.56 cal./cm. 5 5 3 2 0
Exposure Time Retinal D o s e 0 10 3 10 7 10 10 10 14 10
0 . 2 sec. 7.12 cal./cm.* 10 8 8 1 1
Exposure Time Retinal D o s e 0 6 1 6 3 10 7 20 8 10 10 10 12 10 14 10 21 10 28 6 42 4 56 2
s
5 5 7 8 10
0 2 2 9 9
0 . 3 sec. 1 0 . 6 8 cal./cm.» 6 0 6 0 10 0 20 0 8 2 7 3 5 5 10 0 1 9 0 6 4 0 0 2
* Distribution of light-coagulated rabbit e y e s within different groups according t o applied energy. C o l u m n 3 indicates the number of e y e s in which blood circulation is c o m p l e t e l y blocked after various t i m e intervals postcoagulation. C o l u m n 4 g i v e s the n u m b e r of e y e s in which blood circulation w a s not c o m p l e t e l y blocked or has restarted, respectively.
flow was blocked in all experimental eyes immediately after exposure. Three days after light coagulation circulation was restored in 20 percent of the eyes and 10 days after light exposure blood flow had returned in 90 percent of the eyes (table 1). A further increase in retinal dose to 10.68 cal./cm. , by increasing the exposure time to 0.3 s e c , should be regarded as the highest possible intensity that can be employed within that short an exposure time, since further energy increase would result in explosionlike disruption of choroid and retina. 2
282
W A L T E R J. G E E R A E T S , M R I N M A Y G H O S H A N D D U P O N T G U E R R Y ,
III
F i g . 4 (Geeraets, Ghosh and G u e r r y ) . Double light coagulation barrage which has effectively blocked any circulation to the encircled area. N o t e the choroidal rupture at the 11-o'clock position caused by too high intensity.
With such extremely high retinal doses complete blockage of choroidal blood flow was found to occur up to seven days after exposure (fig. 4 ) . From eight to 12 days postcoagulation, an increasing percentage of eyes showed different degrees of new blood circulation (fig. 5 ) . In all but one of the experimental eyes, blood flow had returned after 10 days. In one experimental eye no signs of active blood circulation could be observed 21 days after exposure (table 1 ) .
F i g . S (Geeraets, Ghosh and G u e r r y ) . N e w v e s sel formation within area encircled by heavy double light coagulation barrage 14 days previously.
A s already mentioned, even with such intense coagulation, vessels could be seen passing the light coagulation barrages if a gap was allowed to remain in the inner or outer circle of coagulations. A n interesting finding was that blood circulation peripheral to the barrages showed marked reaction with complete loss of function similar to that present in the central delimited zone. The duration of such changes was also comparable. The early return of blood flow to the area
EFFECT OF LIGHT ON CHOROIDAL
enclosed by coagulations of lower intensity is believed to be caused by reopening of spastic contractions of the vessel walls. Such contractions can be observed ophthalmoscopically when retinal vessels are coagulated. In such instances interruption of the blood column can be visualized but this occurs for only a limited period of time unless large doses are employed. The relatively long period for return of blood circulation after heavy intensities have been administered cannot be explained on the basis of spastic contraction alone. Recanalization and neovascularization take place and increase until adequate nutrition and oxygenation of the now atrophic chorioretinal scar is assured. Necrosis with complete hole formation or other complications, which one might expect following such heavy coagulations with inhibition of blood supply to such a large area, did not occur in any of the experimental eyes. CONCLUSION
From this study it can be concluded that single light coagulation barrages and those of only moderate intensity are ineffective in blocking blood supply to a fundus lesion. The therapeutic effect of such barrages can serve only in destroying peripheral tumor cells that might remain viable, if treatment were limited to the lesion alone. Isolation of such lesions can, however, be achieved, at least temporarily, by means of an extremely heavy double barrage. For clinical purposes such intensities are fraught with danger because of the probability of chorioretinal explosions, massive vitreous hemorrhages a n d / or retinal detachment secondary to hole formation. It might be argued, however, that in such instances a calculated risk may be worth the taking since the only alternative is enucleation. The decision to enucleate or to coagulate
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remains that of the individual ophthalmologist, since no authoritative answer can be given until considerably greater clinical data have been accumulated and evaluated. SUMMARY
The effectiveness of light coagulation barrages on choroidal blood flow was studied in rabbit eyes. It was found that choroidal circulation can be completely blocked for a limited time, providing the following technique is followed. 1. A double line of light coagulation spots has to be employed with no gaping between individual coagulations. 2. Such double barrages must be located outside the fundus area where short ciliary vessels penetrate the sclera. 3. A retinal dose of at least 12 cal./cm. with a delivery time of 0.3 sec. had to be applied for complete chorioretinal vessel obliteration. This dose should be regarded as a maximal allowable intensity since with higher intensities explosionlike disruptions of retina and choroid might result. 4. Recanalization and neovascularization of the chorioretinal area surrounded by the double light coagulation barrage occurred from 10 to 14 days following light coagulation. 5. The clinical use of such an encircling double barrage with high intensities to delimit small malignant neoplasms of retina and choroid is hazardous and may lead to complications such as chorioretinal explosion, massive vitreous hemorrhage, and detachment. Barrages produced with lower energies will not be effective in interrupting the blood supply of the encircled lesion, but may be of value in destroying peripherally located tumor cells. 2
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(19).
REFERENCES
1. Guerry, D . P . , I I I , W i e s i n g e r , H., Geeraets, W . J.: S y m p o s i u m o n lightcoagulation. Internat. Ophth. Clinics, v. I, no. 4, D e c , 1961. 2. M e y e r - S c h w i c k e r a t h , G.: L i g h t Coagulation. S t Louis, M o s b y , 1960. 3. Geeraets, W . J., W i l l i a m s , R. C , Chan, G., H a m , W . T., Guerry, D . , and Schmidt, F . : T h e loss o f light energy in retina and choroid. Α Μ Α A r c h . Ophth., 6 4 : 6 0 6 , 1960.