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Laser Coagulation of the Retina using the Argon Laser
666
AMERICAN JOURNAL OF OPHTHALMOLOGY
been in investigating abnormalities of the retinal circulation. The Wilmer Institute (21205) REFERENCES
1. MacLean, A. L. and Maumenee, A. E. : Hemangioma of the choroid. Am. J. Ophth.50 :3, 1960. 2. Hvvärinen, L. : Circulation in the fundus of the rabbit eye. Acta Ophth. 45 :862, 1967. 3. Haining, W. M. and Lancaster, R. C. : Ad-
MAY, 1969
vanced techniques for fluorescein angiography. Arch. Ophth. 79:10, 1968. 4. Maumenee, A. E. : Fluorescein angiography in the diagnosis and treatment of lesions of the ocular fundus (The 1968 Doyne Lecture). Trans. Ophth. Soc. U.K. 1968 (in press). 5. Gass, J. D. M. : Acute posterior multifocal placoid pigment epitheliopathy. Arch. Ophth. 80: 177, 1968. 6. Jiitte, A. and Lemke, L. : Intravitalfarbung am Augenhintergrund mit Fluoreszein-Natrium. Klin. Mbl. Augenh. 1968, suppl. 49.
LASER COAGULATION O F T H E RETINA USING T H E ARGON M I C H A E L T A L E F F , M.D., E D M O N D J. R I T T E R , M . S e ,
R. J A M E S R O C K W E L L ,
LASER M.Se,
AND B R A N C H C. L O T S P E I C H Cincinnati,
T h e present investigation was undertaken to study the types of chorioretinal lesions produced by the argon laser and the thresh old values of retinal damage from this source. T h e argon laser is a continuous wave light source which produces nine discrete wavelengths that range between 4545 Ä and 5145 Â. T h e entire range of light is well transmitted by the ocular media. 1 It is possi ble that the argon laser source may offer the advantages presented by both the xenon photocoagulator 2 and the present pulsed ruby laser systems 3 while eliminating some of the disadvantages of each. MATERIALS AND METHOD
The laser used for the experiments was a Model 5600 argon ion laser (Spacerays, I n c . ) . T h e system was operated by selecting one of three individual wavelengths of 4765, 4880, 5145 Â and with a mixed beam con taining approximately nine wavelengths be tween 4545 and 5145 Â. I n the latter case 4880 and 5145 Â wavelengths comprised nearly 8 0 % of the total beam. T h e apparatus (fig. 1) was similar to that used by Geeraets and associates* to provide uniform beam From the Department of Ophthalmology, College of Medicine, University of Cincinnati, and the Laser Laboratory, Children's Hospital Research Foundation.
Ohio
density. T h e beam power was monitored continuously and direct visualization of the fundus while producing the lesions was pos sible. Gray chinchilla rabbits weighing ap proximately 2.0 kg were used. Anesthesia was obtained with sodium pentobarbital in jected intravenously and maximum pupillary dilatation was obtained with cyclopentolate 1% and phenylephrine hydrochloride 1 0 % . RESULTS A. T Y P E
OF CHORIORETINAL
LESIONS
PRO
D U C E D BY THE ARGON LASER USING A MIXED BEAM
W i t h a power level of 250 milliwatts and a 1.0 second exposure, a large hemorrhagic lesion was produced. T h e hemorrhage re mained in the subhyaloid region and resorbed over the next several days. At seven days the lesion was healing as an irregularly pigmented scar. W i t h 250 milliwatts power and a 40 millisecond exposure, a lesion was seen immediately following impact, which consisted of a small reddish center sur rounded by a pale halo. Such lesions (fig. 2) are similar in appearance to those produced by the ruby laser. 4 Occasionally the small central hemorrhagic center would spread out to include the halo area. W i t h energy levels of 125 milliwatts and exposures of 40 milliseconds, a pale lesion
VOL. 67, NO. 5
667
LASER COAGULATION OF T H E RETINA POWER MONITOR
FUNDUS CAMERA
LASER BEAM ARTICULATING ARM BEAM ANGLE 25 - 30 Milliradians Fig. 1 (Taleff, Ritter, Rockwell and Lotspeich). Experimental arrangement for eye exposures.
All of the larger lesions healed by seven days as pigmented chorioretinal scars. In the case of some of the very small near-thresh old lesions, it was not possible to identify the lesions visually seven days after treatment. Histologie samples from the lesions pro duced at 125 milliwatts at 40 milliseconds were taken at 48 hours and seven days after
Fig. 2 (Taleff, Ritter, Rockwell and Lotspeich). Fundus photograph of chorioretinal lesions at 250 milliwatts, 40 millisecond exposure immediately fol lowing treatment.
would appear immediately following impact and over the next few minutes it would in crease slightly in size (fig. 3). When the power used was slightly above threshold level, a small pale area was found which was some times not visible for two or three minutes following impact; it usually developed to its full and final size by 20 minutes (fig. 4 ) .
Fig. 3 (Taleff, Ritter, Rockwell and Lotspeich). Fundus photograph of chorioretinal lesions at 125 milliwatts, 40 millisecond exposure five minutes after treatment.
668
AMERICAN JOURNAL OF OPHTHALMOLOGY
MAY, 1969
into the area of the lesion (fig. 5). There is some thrombosis of the smaller vessels of the choriocapillaris but no demonstrable dis ruption of the larger choroidal vessels. A firm chorioretinal scar is noted after seven days, with proliferation of glial and pigment cell elements (fig. 6). These findings are simi lar to those noted with ruby laser lesions.4 Microscopic examination of the threshold le sions after 48 hours shows an accumulation of pale acidophilic edema fluid in the outer layers of the retina and separating it from the pigment epithelium (fig. 7). There is lit tle disruption of the inner layers of the ret ina or of the adjacent choriocapillaris. Fig. 4 (Taleff, Ritter, Rockwell and Lotspeich). Fundus photograph of chorioretinal lesions just above threshold 20 minutes after treatment. treatment. In the 48-hour specimens, there is considerable disruption of all retinal ele ments, with edema and slight hemorrhage
B. THRESHOLD DETERMINATION
In order to establish the level of retinal threshold damage, exposures were made at powers which bracketed the range between the level at which no retinal lesions were ob served and the level at which lesions were observed in 100% of the exposures. Each
Fig. S (Taleff, Ritter, Rockwell and Lotspeich). Photomicrograph of chorioretinal lesion at 125 milliwatts, 40 millisecond exposure 48 hours after treatment (hematoxylin-eosin, χ256).
VOL. 67, NO. 5
LASER COAGULATION OF THE RETINA
669
Fig. 6 (Taleff, Ritter, Rockwell and Lotspeich). Photomicrograph of chorioretinal lesion at 125 milliwatts, 40 millisecond exposure seven days following treatment (hematoxylin-eosin, χ!20).
animal was prepared with sedation and mydriasis as previously described. Twenty laser impacts were placed in an area of the fundus which could be easily found on one field of view with the direct ophthalmoscope. Fol lowing laser impact the area was observed
repeatedly for emergence of visible lesions ; the number of visible lesions were counted after one hour and tabulated. This was done for individual wavelengths of 4765, 4880, and 5145 Â. The results for these three individ ual wavelengths indicate no significant
Fig. 7 (Taleff, Ritter, Rockwell and Lotspeich). Photomicrograph of chorioretinal lesion, threshold-level exposure, 48 hours following treatment (hematoxylin-eosin, X256).
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AMERICAN JOURNAL OF OPHTHALMOLOGY
MAY, 1969
difference in the threshold of damage level between these wavelengths (fig. 8). Figure 9 shows the retinal threshold of damage dose levels for the mixed beam after correction for losses in the ocular media.5 These are in general agreement with the data of Ham and co-workers6 for white light. SUMMARY
0
20
40
60
80
100
Probability of Lesion Formation (Percent) Fig. 8 (Taleff, Ritter, Rockwell and Lotspeich). Probability of irreversible retinal lesions for ex posures of 40 milliseconds for 4765, 4880 and 5145 Â.
ACKNOWLEDGMENT
W e thank Marilyn Franzen for her valuable tech nical contributions to this work.
700 η
= 3.8 milliseconds E 600 500 400
300200
T- 40 milliseconds
100
0
The effects of the argon laser on the ocu lar fundus of the gray chinchilla rabbit were investigated. High-power lesions caused marked disruption of the retina and under lying choriocapillaris, with subhyaloid hem orrhage. Medium- and low-power lesions showed changes similar to those produced by the pulsed ruby laser both grossly and histologically. The threshold of damage agrees closely with that of white light and no sig nificant difference in threshold of damage was found between individual wavelengths of 4765, 4880, 5145 Â and the mixed unfiltered argon beam. College of Medicine (45219)
20
40
60
80
100
Probability Of Lesion Formation (Percent) Fig. 9 (Taleff, Ritter, Rockwell and Lotspeich). Probability of irreversible retinal lesions for expo sures of 40 and 3.8 milliseconds, for mixed argon laser beam.
REFERENCES 1. Geeraets, W. J., Williams, R. C , Chan, F., Ham. W. T., Jr., Guerry, D., I l l , and Schmidt, F. H. : The loss of light energv in retina and choroid, Arch. Ophth. 64:606, 1960. ' 2. Meyer-Schwickerath, G. : Light Coagulation. St. Louis, Mosby, 1960, P. 42. 3. Campbell, C. J., Noyori, K. S., Rittler, M. C. and Koester, C. J. : Clinical use of the laser retinal photocoagulator, Fed. Proc. 24:s-71, 1965. 4. Geeraets, W. J., Ham, W. T., Jr., Williams, R. C , Mueller, H. A., Burkhart, J., Guerry, D., I l l , and Vos, J. J. : Laser versus light coagulator : A fimduscopic and histologie study of chorioretinal injury as a function of exposure time. Fed. Proc. 24 :s-48, suppl. 14, 1965. 5. Geeraets, W. J., Willir.ms, R. C , Chan, G., Ham, W. T., Jr., Guerry, D., I l l , and Schmidt, F. H. : The relative absorption of thermal energy in retina and choroid. Invest. Ophth. 1:340, 1962. 6. Ham, W. T., Jr., Williams, R. C , Mueller, H. A., Guerry, D., I l l , Clarke, A. M. and Geeraets, W. T. : Effects of laser radiation on the mammalian eye.'Tr. N. Y. Acad. Sei. 28:517, 1966.
AMERICAN JOURNAL OF OPHTHALMOLOGY
been in investigating abnormalities of the retinal circulation. The Wilmer Institute (21205) REFERENCES
1. MacLean, A. L. and Maumenee, A. E. : Hemangioma of the choroid. Am. J. Ophth.50 :3, 1960. 2. Hvvärinen, L. : Circulation in the fundus of the rabbit eye. Acta Ophth. 45 :862, 1967. 3. Haining, W. M. and Lancaster, R. C. : Ad-
MAY, 1969
vanced techniques for fluorescein angiography. Arch. Ophth. 79:10, 1968. 4. Maumenee, A. E. : Fluorescein angiography in the diagnosis and treatment of lesions of the ocular fundus (The 1968 Doyne Lecture). Trans. Ophth. Soc. U.K. 1968 (in press). 5. Gass, J. D. M. : Acute posterior multifocal placoid pigment epitheliopathy. Arch. Ophth. 80: 177, 1968. 6. Jiitte, A. and Lemke, L. : Intravitalfarbung am Augenhintergrund mit Fluoreszein-Natrium. Klin. Mbl. Augenh. 1968, suppl. 49.
LASER COAGULATION O F T H E RETINA USING T H E ARGON M I C H A E L T A L E F F , M.D., E D M O N D J. R I T T E R , M . S e ,
R. J A M E S R O C K W E L L ,
LASER M.Se,
AND B R A N C H C. L O T S P E I C H Cincinnati,
T h e present investigation was undertaken to study the types of chorioretinal lesions produced by the argon laser and the thresh old values of retinal damage from this source. T h e argon laser is a continuous wave light source which produces nine discrete wavelengths that range between 4545 Ä and 5145 Â. T h e entire range of light is well transmitted by the ocular media. 1 It is possi ble that the argon laser source may offer the advantages presented by both the xenon photocoagulator 2 and the present pulsed ruby laser systems 3 while eliminating some of the disadvantages of each. MATERIALS AND METHOD
The laser used for the experiments was a Model 5600 argon ion laser (Spacerays, I n c . ) . T h e system was operated by selecting one of three individual wavelengths of 4765, 4880, 5145 Â and with a mixed beam con taining approximately nine wavelengths be tween 4545 and 5145 Â. I n the latter case 4880 and 5145 Â wavelengths comprised nearly 8 0 % of the total beam. T h e apparatus (fig. 1) was similar to that used by Geeraets and associates* to provide uniform beam From the Department of Ophthalmology, College of Medicine, University of Cincinnati, and the Laser Laboratory, Children's Hospital Research Foundation.
Ohio
density. T h e beam power was monitored continuously and direct visualization of the fundus while producing the lesions was pos sible. Gray chinchilla rabbits weighing ap proximately 2.0 kg were used. Anesthesia was obtained with sodium pentobarbital in jected intravenously and maximum pupillary dilatation was obtained with cyclopentolate 1% and phenylephrine hydrochloride 1 0 % . RESULTS A. T Y P E
OF CHORIORETINAL
LESIONS
PRO
D U C E D BY THE ARGON LASER USING A MIXED BEAM
W i t h a power level of 250 milliwatts and a 1.0 second exposure, a large hemorrhagic lesion was produced. T h e hemorrhage re mained in the subhyaloid region and resorbed over the next several days. At seven days the lesion was healing as an irregularly pigmented scar. W i t h 250 milliwatts power and a 40 millisecond exposure, a lesion was seen immediately following impact, which consisted of a small reddish center sur rounded by a pale halo. Such lesions (fig. 2) are similar in appearance to those produced by the ruby laser. 4 Occasionally the small central hemorrhagic center would spread out to include the halo area. W i t h energy levels of 125 milliwatts and exposures of 40 milliseconds, a pale lesion
VOL. 67, NO. 5
667
LASER COAGULATION OF T H E RETINA POWER MONITOR
FUNDUS CAMERA
LASER BEAM ARTICULATING ARM BEAM ANGLE 25 - 30 Milliradians Fig. 1 (Taleff, Ritter, Rockwell and Lotspeich). Experimental arrangement for eye exposures.
All of the larger lesions healed by seven days as pigmented chorioretinal scars. In the case of some of the very small near-thresh old lesions, it was not possible to identify the lesions visually seven days after treatment. Histologie samples from the lesions pro duced at 125 milliwatts at 40 milliseconds were taken at 48 hours and seven days after
Fig. 2 (Taleff, Ritter, Rockwell and Lotspeich). Fundus photograph of chorioretinal lesions at 250 milliwatts, 40 millisecond exposure immediately fol lowing treatment.
would appear immediately following impact and over the next few minutes it would in crease slightly in size (fig. 3). When the power used was slightly above threshold level, a small pale area was found which was some times not visible for two or three minutes following impact; it usually developed to its full and final size by 20 minutes (fig. 4 ) .
Fig. 3 (Taleff, Ritter, Rockwell and Lotspeich). Fundus photograph of chorioretinal lesions at 125 milliwatts, 40 millisecond exposure five minutes after treatment.
668
AMERICAN JOURNAL OF OPHTHALMOLOGY
MAY, 1969
into the area of the lesion (fig. 5). There is some thrombosis of the smaller vessels of the choriocapillaris but no demonstrable dis ruption of the larger choroidal vessels. A firm chorioretinal scar is noted after seven days, with proliferation of glial and pigment cell elements (fig. 6). These findings are simi lar to those noted with ruby laser lesions.4 Microscopic examination of the threshold le sions after 48 hours shows an accumulation of pale acidophilic edema fluid in the outer layers of the retina and separating it from the pigment epithelium (fig. 7). There is lit tle disruption of the inner layers of the ret ina or of the adjacent choriocapillaris. Fig. 4 (Taleff, Ritter, Rockwell and Lotspeich). Fundus photograph of chorioretinal lesions just above threshold 20 minutes after treatment. treatment. In the 48-hour specimens, there is considerable disruption of all retinal ele ments, with edema and slight hemorrhage
B. THRESHOLD DETERMINATION
In order to establish the level of retinal threshold damage, exposures were made at powers which bracketed the range between the level at which no retinal lesions were ob served and the level at which lesions were observed in 100% of the exposures. Each
Fig. S (Taleff, Ritter, Rockwell and Lotspeich). Photomicrograph of chorioretinal lesion at 125 milliwatts, 40 millisecond exposure 48 hours after treatment (hematoxylin-eosin, χ256).
VOL. 67, NO. 5
LASER COAGULATION OF THE RETINA
669
Fig. 6 (Taleff, Ritter, Rockwell and Lotspeich). Photomicrograph of chorioretinal lesion at 125 milliwatts, 40 millisecond exposure seven days following treatment (hematoxylin-eosin, χ!20).
animal was prepared with sedation and mydriasis as previously described. Twenty laser impacts were placed in an area of the fundus which could be easily found on one field of view with the direct ophthalmoscope. Fol lowing laser impact the area was observed
repeatedly for emergence of visible lesions ; the number of visible lesions were counted after one hour and tabulated. This was done for individual wavelengths of 4765, 4880, and 5145 Â. The results for these three individ ual wavelengths indicate no significant
Fig. 7 (Taleff, Ritter, Rockwell and Lotspeich). Photomicrograph of chorioretinal lesion, threshold-level exposure, 48 hours following treatment (hematoxylin-eosin, X256).
670
AMERICAN JOURNAL OF OPHTHALMOLOGY
MAY, 1969
difference in the threshold of damage level between these wavelengths (fig. 8). Figure 9 shows the retinal threshold of damage dose levels for the mixed beam after correction for losses in the ocular media.5 These are in general agreement with the data of Ham and co-workers6 for white light. SUMMARY
0
20
40
60
80
100
Probability of Lesion Formation (Percent) Fig. 8 (Taleff, Ritter, Rockwell and Lotspeich). Probability of irreversible retinal lesions for ex posures of 40 milliseconds for 4765, 4880 and 5145 Â.
ACKNOWLEDGMENT
W e thank Marilyn Franzen for her valuable tech nical contributions to this work.
700 η
= 3.8 milliseconds E 600 500 400
300200
T- 40 milliseconds
100
0
The effects of the argon laser on the ocu lar fundus of the gray chinchilla rabbit were investigated. High-power lesions caused marked disruption of the retina and under lying choriocapillaris, with subhyaloid hem orrhage. Medium- and low-power lesions showed changes similar to those produced by the pulsed ruby laser both grossly and histologically. The threshold of damage agrees closely with that of white light and no sig nificant difference in threshold of damage was found between individual wavelengths of 4765, 4880, 5145 Â and the mixed unfiltered argon beam. College of Medicine (45219)
20
40
60
80
100
Probability Of Lesion Formation (Percent) Fig. 9 (Taleff, Ritter, Rockwell and Lotspeich). Probability of irreversible retinal lesions for expo sures of 40 and 3.8 milliseconds, for mixed argon laser beam.
REFERENCES 1. Geeraets, W. J., Williams, R. C , Chan, F., Ham. W. T., Jr., Guerry, D., I l l , and Schmidt, F. H. : The loss of light energv in retina and choroid, Arch. Ophth. 64:606, 1960. ' 2. Meyer-Schwickerath, G. : Light Coagulation. St. Louis, Mosby, 1960, P. 42. 3. Campbell, C. J., Noyori, K. S., Rittler, M. C. and Koester, C. J. : Clinical use of the laser retinal photocoagulator, Fed. Proc. 24:s-71, 1965. 4. Geeraets, W. J., Ham, W. T., Jr., Williams, R. C , Mueller, H. A., Burkhart, J., Guerry, D., I l l , and Vos, J. J. : Laser versus light coagulator : A fimduscopic and histologie study of chorioretinal injury as a function of exposure time. Fed. Proc. 24 :s-48, suppl. 14, 1965. 5. Geeraets, W. J., Willir.ms, R. C , Chan, G., Ham, W. T., Jr., Guerry, D., I l l , and Schmidt, F. H. : The relative absorption of thermal energy in retina and choroid. Invest. Ophth. 1:340, 1962. 6. Ham, W. T., Jr., Williams, R. C , Mueller, H. A., Guerry, D., I l l , Clarke, A. M. and Geeraets, W. T. : Effects of laser radiation on the mammalian eye.'Tr. N. Y. Acad. Sei. 28:517, 1966.