© 1991 S. K arger A G. Basel 0030-3755/91/2021-0010 $2.75/0
Ophthalmologica 1991:202:10-17
Function of the Diabetic Retina after Panretinal Argon Laser Photocoagulation Influence of the Intensity of the Coagulation Spots Volker Seiberth, Evangelos Alexandridis Univcrsitäts-Augenklinik. Heidelberg. BRD
Key Words. Diabetic retinopathy • Argon laser photocoagulation • High-energy coagulation • Randomized clinical trial • Electroretinography • Electro-oculography
Introduction Ever since photocoagulation was intro duced by Meyer-Schwickerath [33] for the therapy of diabetic retinopathy, this form of treatment is being increasingly used. It has been validated by both large, controlled random clinical studies [5, 6, 9-12, 44] and by numerous smaller studies [3, 24, 35, 37, 41]. In addition to xenon arc, argon laser coag ulation is mainly used today. The coagulation parameters reported for laser coagulation dif
fer widely [2, 29, 31]. Various spot locations in the diabetic retina [14,18, 24] were compared. The influence of exposure time was also ex plored, using the same energy level in a single effect [34], The goal of other investigations was determine the role of the size and density of the coagulation spots [43]. The intensity of the laser spots is also an important coagulation parameter because it determines the volume of the coagulation spot in addition to the diameter of the spot and the duration of the effect. The total volume of
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Abstract. To investigate the influence of the intensity of coagulation spots on retinal function and the clinical course after panretinal argon laser photocoagulation in diabetic retinopathy, we conducted a prospective study in 24 eyes of 12 diabetics. One eye was treated with moderate spots (average: 300 mW), the fellow eye was coagulated with intense spots (average: 600mW). The spot size was identical in both eyes. Subjective parameters (visual acuity, perimetry), as well as objective functions (ERG, EOG) and the clinical course, were studied preoperatively and on a regular base with a follow-up of 12 months. Visual acuity and fundus findings deteriorated less often in eyes coagulated with intense spots. Visual field loss, however, was more prevalent in eyes treated with intense spots. Early treatment complications only occurred with high-energy coag ulation. For this reason, high-energy spots should not be used even though they might be indicated theoretically.
Function of the Diabetic Retina after Panretinal Argon Laser Photocoagulation
coagulated retina, however, determines the ef fectiveness of the procedure. The total amount of coagulated surface is of secondary impor tance. The goal of the present prospective study was to establish the influence of the intensity of the coagulation spot on the postoperative course.
Patients and Methods Patients In 1986. 12 patients of the University of Heidelberg Eye Hospital with advanced prepoliferative diabetic ret inopathy were selected: the retinopathy was equal on both sides. No previous photocoagulation had been car ried out on any of these patients. The refracting media were clear. Visual acuity was 0.5 or better and was nearly the same for both eyes of any given patient. The patients were between 33 and 72 years of age (mean 53.7 years). Nine patients were men and 3 women. Seven patients had diabetes mellitus, type I, and 5 patients type II. In 8 patients the diabetes mellitus was controlled with insulin and in 4 with oral antidiabetic medicine. The diabetes was diagnosed 1-21 years ago (mean 13 years).
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Coagulation. Coagulation treatment was accom plished with the Britt Argon Laser (Model 150). Avoid ing the region inside the great vascular arcades and leaving a distance of a papillary diameter to the papilla, coagulation was disseminated into all four quadrants with the Goldmann contact lens in 2-3 sessions per eye. The pulse duration was 0.2 s. The energy level was es tablished individually for each eye that was coagulated with comparatively less intensity; this level was chosen in such a way that the coagulation spots were grayishwhite. This coagulation technique was carried out using an average intensity of 300 mW (range of 200-600 mW) and 100 pm beam diameter on one eye and a significant ly higher dose on the fellow eye: average energy at about 600 mW (range of 400-900 mW) and beam diameter 50 pm. The beam diameter was varied in order to ex clude the possibility of falsifying the results through the influence of varying spot size due to coagulation in tensity. As a result, the coagulation spot size was identi cal at the two energy levels. An equal area was coagulat ed in both eyes of a given patient. The distribution, whether the right or left eye w'as coagulated with a high or low dose, was by chance.
Results
Methods Investigation. The patients were examined before treatment as well as on one of the first 3 days follow ing coagulation therapy. Further follow-up examina tions took place 3. 6, and 12 months after laser ther apy. The following examinations were carried out: - visual acuity for both far and near vision: - computed static perimetry with the Tübingen Auto matic Perimeter (30° field of vision, luminance cate gory 3): - biomicroscopy of the anterior eye segment: - tonometry; - ophthalmoscopy of the fundus in mydriasis; - photodocumentation of the fundus findings: - clectroretinography (ERG); - electro-oculography (EOG). and - fluorescein angiography in selected patients.
The mean preoperative visual acuity was 0.73 and varied between 0.5 and 1.0. The evolu tion of visual acuity during the follow-up can be seen in figure 1. Twelve months after coagulation, there was no change in visual acuity in 13 of 24 eyes in comparison with the preoperative findings. Of them, 9 eyes (37.5%) belonged to the group coagulated with higher energy and 4 eyes (16.7%) to the group coagulated with less in tense spots. In 10 eyes (41.7%), the visual acu ity was found to be worse at this point in time by more than two lines. Three of the eyes (12.5%) were coagulated with high energy and 7 with low energy. After the same time period, 1eye (4.2%) improved by more than two lines; it had been coagulated using low energy.
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Visual Acuity
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Visual Field
Examination of the visual field with the Tübingen Automatic Perimeter showed only minor changes in 5 eyes (20.8%) a few days after coagulation in comparison with the pre operative findings. Of these, 2 eyes (8.3%) were treated with high-energy coagulation and 3 (12.5%) with low energy. In the remaining 19 eyes (79.2%), more or less pronounced scoto ma was detected. Of these, 10 eyes (41.7%) had been coagulated with high energy and 9 (37.5%) with low energy. Twelve months after coagulation, 13 eyes (54.2%) were found to show no or little change in comparison with the preoperative findings. Of these, 5 eyes (20.8%) had been coagulated with high-energy coagulation spots and 8 with low-energy spots. Eleven eyes (45.8%) showed clear-cut worsening of the visual field: 8 eyes (33.3%) belonging to the group coagulated with high energy and 4 (16.7%) to the group receiving low energy coagulation. With regard to pairs of eyes, in 8 pairs (66.7%), the findings were the same in both eyes after 12 months. In 3 pairs of eyes (25%), the eye coagulated with high energy was found to be significantly worse in comparison with the fellow eye: in 1 pair of eyes (8.3%), the eye treated with less intense spots had worse findings than the fellow eye.
Fig. 2. ERG: mean a- and b-wave. Solid line: highenergy coagulation; dashed line: low-energy coagula tion.
Electroretinography
Preoperatively, clear amplitude differences were demonstrated interindividually in both the a- and b-waves. The mean values of the amplitudes, did not differ significantly in the two groups. The amplitudes were normal in 20 eyes (83.3%) and pathological in 4 eyes (16.7%). Within 3 days after the operation and at later examinations, a clear-cut deterioration of the a- and b-wave was detected. The eyes treated with intense coagulation spots showed slightly lower mean potentials in the a- and b-waves than did eyes coagulated with weaker energy (fig. 2). Electro-Oculography
The mean values of pre- and postoperative potentials as well as the L/D ratio are shown in table 1. The Arden quotient showed an appre ciable coagulation-dependent postoperative reduction in comparison with the preoperative value. The light increase was then hardly rec ognizable. There were no significant differ ences between the two groups (fig. 3). Complications in Coagulation Treatment
All eyes that received fairly strong coag ulation spots proved to be free of complica-
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Fig. 1. Mean visual acuity. Solid line: high-energy coagulation: dashed line: low-energy coagulation.
Function of the Diabetic Retina after Panretinal Argon Laser Photocoagulation
Table 1. EOG: mean values of resting potential and L/D ratio (n = 24) Laser PrcPostoperatively energy operatively < 3 3 6 9 days months Resting potential pV
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High Low
383 402
200 338 215 293
287 313
240 271 260 294
L/D ratio High Low
2.73 2.78
1.42 1.61 1.37 1.74
1.70 1.48 1.35 1.82 1.53 1.31
tions. In contrast, in the group of 12 eyes treat ed with high-energy laser spots, 3 eyes (14.7%) had a small amount of localized choroidal bleeding; in 4 eyes (33.3%) there was small intra- and preretinal bleeding, and in 1 eye (8.3%) there was choroidal detachment. In 1 eye (8.3%) secondary angle closure occurred, which resolved after conservative treatment and a return to normal of the retinal and cho roidal swelling. No operative treatment was required. Postoperative Findings
Twelve months after coagulation, 13 eyes (54.2%) showed no change in comparison with the preoperative situation. Eleven eyes
(45.8%) became worse in the course of the year after coagulation: aneurysms, spot and blot hemorrhages, hard exsudate, chronic retinal edema at the posterior pole, and cystoid mac ular edema were responsible. Of the 11 eyes (45.8%) that had become worse, 3 (12.57%) had been treated with intense coagulation spots and 8 (33.3%) with less intense spots. When comparing eye pairs, 5 pairs (41.7%) showed equal findings in both eyes. In 2 pairs of eyes (16.6%), the eye treated with high-en ergy coagulation showed worse findings; in 5 pairs (41.7%) the eye coagulated with low ener gy showed worse findings.
Discussion Experience to date with laser coagulation supports the assumption that not only the ex tent of the retinal area coagulated but also the volume of coagulation determine the effective ness of this method of treating diabetic reti nopathy. Using the same spot diameter, the volume of coagulation is dependent upon the exposure time and the energy applied. When the effect of the energy is minor, the volume of the coagulation spot after absorp tion of the light energy in the melanin of the retinal pigment epithelium and the uveal mela nocytes is relatively low [17]. In addition to the retinal pigment epithelium, only the exterior layer of the sensory retina is damaged. Only with very high intensity is the nerve fiber layer also involved [13, 45]. More cells in the retina are destroyed by high-energy coagulation due to greater spot volume. Although the receptor layer has a rel atively high requirement for oxygen, the ox ygen requirement in the remaining retina will be lower than in coagulation using less energy; this results in lower spot volume and damage
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Fig. 3. EOG: mean L/D ratio. Solid line: high-ener gy coagulation; dashed line: low-energy coagulation.
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to the receptor layer alone. Since the effect of photocoagulation in diabetic retinopathy is re ached, among others, through improvement in the oxygen supply to the remainder of the reti na, greater therapeutic success would then be expected in coagulation using higher energy. Diffusion of the choroidea into the retina, as can be demonstrated via fluorescence an giography, may have an influence on the course of diabetic retinopathy. Diffusion comes into play if the retinal pigment epitheli um is destroyed as a barrier through intense coagulation [39]. In the same way, after high-energy photo coagulation, the neovascularization extending from the choroid ruptures Bruch's membrane and the pigment epithelium in the direction of the retina. These new vessel formations may also have an effect on the pathological metabol ic processes that occur in diabetes mellitus [8], Thus there are some reasons for applying relatively high-energy coagulation spots in dis seminated coagulation for the treatment of diabetic retinopathy. Such intense spots may be achieved by extending the exposure time or increasing the energy used. The influence of exposure time on the clin ical course in patients with proliferative diabet ic retinopathy has already been investigated by Meyer-Schwickerath et al. [34]. In their results the variable effects of different coagulation techniques were attributed solely to a longer exposure time. In reality, however, coagula tion spots with varying exposure times and dif ferent intensities were compared. A more fa vorable course was observed in eyes that were coagulated with a longer exposure time and therefore greater energy. If the application time is kept constant, the true influence of applying different energy lev els can be investigated. The goal of our pro spective study was therefore to investigate the
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course of the retinopathy and retinal function under these given conditions. If a clear-cut difference in energy is selected using equal exposure times and an identical laser beam diameter, the diameter of the re sulting coagulation spot is greater. This, in turn, influences individual retinal function tests [43]. For this reason, we chose a smaller laser beam diameter for coagulation with greater energy in order to balance the diame ter of the spots created. After laser coagulation for diabetic retinop athy, a lasting reduction in visual acuity often occurs: the incidence is given as between 3 and 25.2% [9, 26, 32, 43]. Our investigation showed that in the following days after the operation a decrease in visual acuity occurred less often in the group coagulated with intense spots than in the group of eyes coagulated with moderate spots, although one could expect more pronounced coagulation-dependent ede ma, which is the cause of the decrease in visual function. After 1 year, visual acuity deteriorat ed less frequently in the group of eyes treated with high-energy spots. A variable amount of visual field loss is often found in diabetic retinopathy, and the extent of the loss depends on the severity of the illness [1. 2, 7, 16, 21, 40, 46, 48]. After panretinal laser coagulation, prolonged additional scotoma can be detected in some patients [1,2,7,16,20,43]. In the present investigation, this was also ver ified by means of computed static perimetry. When comparing the two coagulation methods, no differences in the degree of functional dis turbance could be determined a few days after treatment. However, after the coagulationcaused edema in the retina had receded in the course of months and only the scar-caused sco toma could be detected, 1 year postoperatively heavily coagulated eyes showed appreciably more loss in visual field than the fellow eyes.
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In diabetic retinopathy, the amplitudes of the a- and b-waves of the ERG have been de scribed as normal [25,38,47] or as reduced [15, 19,27,36]. After panretinal photocoagulation, the ERG is permanently reduced [2, 7, 15, 25, 27, 36, 38]. In our patients, the preoperative amplitudes were normal in 20 eyes (83.3%) and pathological in 4 eyes (16.7%). After treat ment, when the mean a- and b-wave potentials were much lower than before treatment, the a-wave potential was shown to be compara tively smaller in eyes coagulated with highenergy laser spots. This difference is even clearer in the potentials of the b-wave. These results show that more severe damage occurs in the middle retinal layers with the use of high-energy coagulation. In eyes with diabetic retinopathy, the rest ing potential and Arden quotient of the EOG are reduced in relationship to the severity of the disease [4, 7, 19, 23, 42]. Also, in our pa tients the resting potential was preoperatively found to be pathological in 5 eyes (20.8%). Postoperatively in 2 eyes (8.3%), the L/D ratio was hardly reduced at the beginning, which has been established by other authors as well [4, 7, 42]. They also found that this parameter shows a certain amount of recovery in the course of months [43], a finding verfied in the present investigation. The two coagulation methods showed no differences. This is an indication that the calculated and actual surfaces of the damaged pigment epithelium are almost the same in both eyes of a given patient. The transient complications caused by laser coagulation can be multiple [20,22,28,49] and the complication rate depends on the amount of energy used. Small retinal and choroidal hemorrhages, choroidal detachment, and sec ondary angle closure only occurred in our pa tients if they had been treated with intense spots.
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Also, the repair processes of the retina after photocoagulation are energy dependent. The use of moderately intense spots produces full thickness defects in the retina, in which appar ently firm retinal adhesions arise. However, the use of very strong coagulation leads to the retina losing its ability to form glial scars. The retinal pigment epithelium is then only source of the retinal repair process. When such in tense spots are used, preretinal glial mem branes can often be observed that have a tan gential pulling effect on the retina [45]. In the present study, the number of eyes investigated was small. Nevertheless, the hy potheses appear to have been confirmed due to our findings that strong coagulation spots are advantageous in the clinical course of dia betic retinopathy even if visual field loss occurs appreciably more often 1year later than in eyes coagulated with less intense spots. Early coag ulation complication such as hemorrhages in the retina and choroid and angle closure, as well as late complications with the formation of preretinal, glial membranes with a pulling effect, occur only after very high-energy coag ulation. Even so, when eyes with diabetic reti nopathy are coagulated with intense spots, they are less likely to deteriorate, at a later time, than the fellow eye. For these complica tions, very-high-energy coagulation with a rel atively short exposure time does not appear to be indicated. This is the reason why we did not extend our study to include a large number of patients and why we do not recommend coag ulation with very intense spots even though theoretical considerations indicate that this form of coagulation might be quite advanta geous. Instead, the spots should be smaller [43] and of average energy, as demonstrated by the results to date which, however, arc not significant on account of the small number of patients.
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Function of the Diabetic Retina after Panretinal Argon Laser Photocoagulation
Acknowledgement We thank Ms. U. Schibel for her help with the electrophysiological findings.
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References 1 Becker H, Schmitz J : Computergesteuerte quantita tiv-statische Perimetrie nach panretinaler ArgonLaser-Koagulation bei Retinopathia diabetica. Klin Monatsbl Augenheilkd 1988;192:204-207. 2 Benson WE, Brown GC, Tasman W: Diabetes and Its Ocular Complications. Philadelphia, Saunders, 1988, pp 128-153. 3 Blankenship GW: Diabetic macular edema and ar gon laser photocoagulation: A prospective rando mized study. Ophthalmology 1979:86:69-75. 4 Bonnet M, Cabon-Amon F: Evolution de l'électrooculogramme après photocoagulation pan-réti nienne. J Fr Ophthalmol 1980:3:349-352. 5 British Multicentre Study Group: Proliferative dia betic retinopathy: Treatment with xenon-arc photo coagulation. Interim report of multicentre rando mised controlled clinical trial. Br Med J 1977;i:739741. 6 British Multicentre Study Group: Photocoagulation for proliferative diabetic retinopathy: A randomised controlled clinical trial using xenon arc. Diabetologia 1984;26:109-115. 7 Cambic E: Functional results following argon laser photocoagulation for diabetic retinopathy; in Little HL, Jack RL, Patz A, Forsham PH (eds): Diabetic Retinopathy. New York Thieme & Stratton, 1984, pp 274-284. 8 Deufrains A, Dietze U, Jütte A: Was vermag die Fotokoagulation und was bewirkt sie? Klin Mo natsbl Augenheilkd 1980;177:487-491. 9 Diabetic Retinopathy Study Research Group: Pre liminary report on effect of photocoagulation ther apy. Am J Ophthalmol 1976;81:383-396. 10 Diabetic Retinopathy Study Research Group: Pho tocoagulation treatment of proliferative diabetic ret inopathy: the second report of diabetic retinopathy study findings. Ophthalmology 1978:85:82-106. 11 Diabetic Retinopathy Study Research Group: Pho tocoagulation treatment of proliferative diabetic ret inopathy. Ophthalmology 1981:88:583-600. 12 Early Treatment Diabetic Retinopathy Study Re
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search Group: Photocoagulation for diabetic mac ular edema. Arch Ophthalmol 1985:103:1796-1806. Domarus D von, Naumann GOH: Trauma, Ope rationen und Wundheilung des Auges; in Naumann GOH (ed): Pathologie des Auges. Berlin Springer, 1980, pp 176-239. François J, Cambie E: Argon laser photocoagula tion in diabetic retinopathy. A comparative study of three different methods of treatment. Metab Oph thalmol 1977;1:125-130. François J, De Rouck A, Cambie E, CastanheiraDinis A: Electrophysiological studies before and af ter argon-laser photocoagulation in diabetic retinop athy. Ophthalmologica 1978:176:133-144. Frank RN: Visual fields and electroretinography fol lowing extensive photocoagulation. Arch Ophthal mol 1975:93:591-598. Geeraets WJ, Williams RC. Chan G. Ham WT Jr, Guerry DP III. Schmidt FH: The relative absorption of thermal energy in retina and choroid. Invest Oph thalmol 1962;1:340-347. Gerke E, Bornfeld N, Meyer-Schwickerath G: Die Bedeutung der Lokalisation der Photokoagulations herde bei der proliferativen diabetischen Retino pathie. Fortschr Ophthalmol 1985:82:109—111. Gliem H, Möller DE, Kietzmann G: Die bioelek trische Aktivität der Netzhaut bei der diabetischen Retinopathie. Acta Ophthalmol 1971;49:353-363. Goldberg MF, Herbst RW: Acute complications of argon laser coagulation. Arch Ophthalmol 1973; 89:311-318. Grange JD, Leonhardt C, Taillanter-Francoz N: Evolution de la courbe de périmétrie statique après photocoagulation pan-rétinienne. Bull Soc Ophtalmol France 1981:81:537-538. Hamikon AM, Blach RK: The technique and in dications for photocoagulation in diabetic retinopa thy. II. The treatment of diabetic retinopathy. Int Ophthalmol 1979:2:85-97. Henkes HE, Houtsmuller AJ: Fundus diabeticus. An evaluation of the preretinopathic stage. Am J Ophthalmol 1965;60:662-670. Kiemen C, Kiemen UM, Prskavec FH, Gnad HD: Verlaufsbeobachtungen zentraler diabetischer Netz hautveränderungen nach peripherer Photokoagula tion. Klin Monatsbl Augenheilkd 1985:187:435-436. Li XX. Foerster MH. Bornfeld N, Gerke E: Elektrophysiologische Untersuchungen an Patienten mit diabetischer Retinopathie. Fortschr Ophthalmol 1985:82:293-297.
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Function of the Diabetic Retina after Panretinal Argon Laser Photocoagulation
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nal diffusion of peroxidase before and after photo coagulation. Invest Ophthalmol 1971;10:489-495. Prskavec FH, Fulmek R, Kiemen C, Stelzer N: Ver änderungen des Gesichtsfeldes und der Dunkel adaption nach panretinaler Photokoagulation bei diabetischer Retinopathie. Klin Monatsbl Augenheilkd 1986;189:385-387. Reeser F, Fleischman J. Williams GA. Goldman A: Efficacy of argon laser photocoagulation in the treatment of circinatc diabetic retinopathy. Am J Ophthalmol 1981:92:762-767. Scherfig E, Krogh E: EOG changes in photocoag ulation of diabetic retinopathy. Acta Ophthalmol 1981;59:917-920. Seiberth V, Alexandridis E, Feng W: Function of the diabetic retina after panretinal argon laser coagula tion. Graefes Arch Clin Exp Ophthalmol 1987; 225:385-390. Stenkula S: Photocoagulation in diabetic retinopa thy. A multicentre study in Sweden. Acta Ophthal mol [Suppl] (Copcnh) 1984;162:1-100. Wallow IH: Long-term changes in photocoagulation burns. Dev Ophthalmol 2:318-327. Wisznia KI, Lieberman TW, Leopold IH: Visual fields in diabetic retinopathy. Br J Ophthalmol 1971;55:183-188. Yonemura D. Aoki T, Tsuzuki K: Electroretinogram in diabetic retinopathy. Arch Ophthalmol 1962;68:49-54. Zaluski S, Marcil G, Lamer L, Lambert J: Etude du champ visuel en périmétrie statique automatisée après photocoagulation panrétinienne chez le diabé tique. J Fr Ophtalmol 1986;9:395-401. Zweng HC, Little HL, Hammond AH: Complica tions of argon laser photocoagulation. Trans Am Acad Ophthalmol Otolaryngol 1974:78:195-204.
Received: August 27,1990 Accepted: September 10,1990 Dr. med. Volker Seiberth Universitäts- Augenklinik Direktor: Prof. Dr. med. H. Liesenhoff Klinikum Mannheim Fakultät für Klinische Medizin der Universität Heidelberg Theodor-Kutzer-Ufer D-W-6800 Mannheim (FRG)
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26 Liang JC, Goldberg MF: Treatment of diabetic reti nopathy. Diabetes 1980;29:841-851. 27 Liang JL. Fishman GA, Huamonte FU, Anderson RJ: Comparative electroretinograms in argon laser and xenon arc panretinal photocoagulation. Br J Ophthalmol 1983:67:520-525. 28 Little HL: Complications of argon laser photocoag ulation in the treatment of diabetic retinopathy; in Little HL. Jack RL. Patz A. Forsham PH (eds): Diabetic Retinopathy; New York, Thiemc & Strat ton, 1984, pp 285-296. 29 Little HL: Proliferative diabetic retinopathy: Patho genesis and treatment: in Little HL. Jack RL. Patz A, Forsham PH (eds): Diabetic Retinopathy. New York. Thieme & Stratton, 1984. pp 257-273. 30 Little HL: Treatment of proliferative diabetic reti nopathy. Long-term results of argon laser photo coagulation. Ophthalmology 1985:92:279-293. 31 Little HL, Zweng HC, Jack RL, Vassiliadis A: Tech niques of argon laser photocoagulation of diabetic new vessels. Am J Ophthalmol 1976;82:675-683. 32 McDonald HR. Schatz H: Visual loss following pan retinal photocoagulation for proliferative diabetic retinopathy. Ophthalmology 1985;92:388-393. 33 Meyer-Schwickerath G: Lichtkoagulation bei Reti nopathia diabetica; in Meyer-Schwickerath G: Lichtkoagulation. Enke, Stuttgart, 1959, pp 61-62. 34 Meyer-Schwickerath GRE, Gerke E, Bornfeld N: Dosiology of photocoagulation in proliferative dia betic retinopathy. A prospective study of 20 cases of type I diabetes. Proc Vllth Congr Eur Soc Ophthal mology. Helsinki. 1985. pp 112-113. 35 O'Donoghuc HN: Laser treatment in diabetic reti nopathy. Trans Ophthalmol Soc UK 1982:102:468470. 36 Ogden TE. Callahan F, Riekhof FT: The clectroretinogram after peripheral retinal ablation in diabetic retinopathy. Am J Ophthalmol 1976:81:397-402. 37 Okun E, Johnston GP, Boniuk 1. Arribas NP, Escoffery RF, Grand G: Xenon arc photocoagulation of proliferative diabetic retinopathy. A review of 2,688 consecutive eyes in the format of the Diabetic Retinopathy Study. Ophthalmology 1984:91:1458— 1463. 38 Perlman I, Gdal-On M, Miller B, Zonis S: Retinal function of the diabetic retina after argon laser pho tocoagulation assessed electroretinographically. Br J Ophthalmol 69:240-246. 39 Peyman GA, Spitznas M. Straatsma BR: Choriorcti-
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Ophthalmologica 1991:202:10-17
Function of the Diabetic Retina after Panretinal Argon Laser Photocoagulation Influence of the Intensity of the Coagulation Spots Volker Seiberth, Evangelos Alexandridis Univcrsitäts-Augenklinik. Heidelberg. BRD
Key Words. Diabetic retinopathy • Argon laser photocoagulation • High-energy coagulation • Randomized clinical trial • Electroretinography • Electro-oculography
Introduction Ever since photocoagulation was intro duced by Meyer-Schwickerath [33] for the therapy of diabetic retinopathy, this form of treatment is being increasingly used. It has been validated by both large, controlled random clinical studies [5, 6, 9-12, 44] and by numerous smaller studies [3, 24, 35, 37, 41]. In addition to xenon arc, argon laser coag ulation is mainly used today. The coagulation parameters reported for laser coagulation dif
fer widely [2, 29, 31]. Various spot locations in the diabetic retina [14,18, 24] were compared. The influence of exposure time was also ex plored, using the same energy level in a single effect [34], The goal of other investigations was determine the role of the size and density of the coagulation spots [43]. The intensity of the laser spots is also an important coagulation parameter because it determines the volume of the coagulation spot in addition to the diameter of the spot and the duration of the effect. The total volume of
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Abstract. To investigate the influence of the intensity of coagulation spots on retinal function and the clinical course after panretinal argon laser photocoagulation in diabetic retinopathy, we conducted a prospective study in 24 eyes of 12 diabetics. One eye was treated with moderate spots (average: 300 mW), the fellow eye was coagulated with intense spots (average: 600mW). The spot size was identical in both eyes. Subjective parameters (visual acuity, perimetry), as well as objective functions (ERG, EOG) and the clinical course, were studied preoperatively and on a regular base with a follow-up of 12 months. Visual acuity and fundus findings deteriorated less often in eyes coagulated with intense spots. Visual field loss, however, was more prevalent in eyes treated with intense spots. Early treatment complications only occurred with high-energy coag ulation. For this reason, high-energy spots should not be used even though they might be indicated theoretically.
Function of the Diabetic Retina after Panretinal Argon Laser Photocoagulation
coagulated retina, however, determines the ef fectiveness of the procedure. The total amount of coagulated surface is of secondary impor tance. The goal of the present prospective study was to establish the influence of the intensity of the coagulation spot on the postoperative course.
Patients and Methods Patients In 1986. 12 patients of the University of Heidelberg Eye Hospital with advanced prepoliferative diabetic ret inopathy were selected: the retinopathy was equal on both sides. No previous photocoagulation had been car ried out on any of these patients. The refracting media were clear. Visual acuity was 0.5 or better and was nearly the same for both eyes of any given patient. The patients were between 33 and 72 years of age (mean 53.7 years). Nine patients were men and 3 women. Seven patients had diabetes mellitus, type I, and 5 patients type II. In 8 patients the diabetes mellitus was controlled with insulin and in 4 with oral antidiabetic medicine. The diabetes was diagnosed 1-21 years ago (mean 13 years).
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Coagulation. Coagulation treatment was accom plished with the Britt Argon Laser (Model 150). Avoid ing the region inside the great vascular arcades and leaving a distance of a papillary diameter to the papilla, coagulation was disseminated into all four quadrants with the Goldmann contact lens in 2-3 sessions per eye. The pulse duration was 0.2 s. The energy level was es tablished individually for each eye that was coagulated with comparatively less intensity; this level was chosen in such a way that the coagulation spots were grayishwhite. This coagulation technique was carried out using an average intensity of 300 mW (range of 200-600 mW) and 100 pm beam diameter on one eye and a significant ly higher dose on the fellow eye: average energy at about 600 mW (range of 400-900 mW) and beam diameter 50 pm. The beam diameter was varied in order to ex clude the possibility of falsifying the results through the influence of varying spot size due to coagulation in tensity. As a result, the coagulation spot size was identi cal at the two energy levels. An equal area was coagulat ed in both eyes of a given patient. The distribution, whether the right or left eye w'as coagulated with a high or low dose, was by chance.
Results
Methods Investigation. The patients were examined before treatment as well as on one of the first 3 days follow ing coagulation therapy. Further follow-up examina tions took place 3. 6, and 12 months after laser ther apy. The following examinations were carried out: - visual acuity for both far and near vision: - computed static perimetry with the Tübingen Auto matic Perimeter (30° field of vision, luminance cate gory 3): - biomicroscopy of the anterior eye segment: - tonometry; - ophthalmoscopy of the fundus in mydriasis; - photodocumentation of the fundus findings: - clectroretinography (ERG); - electro-oculography (EOG). and - fluorescein angiography in selected patients.
The mean preoperative visual acuity was 0.73 and varied between 0.5 and 1.0. The evolu tion of visual acuity during the follow-up can be seen in figure 1. Twelve months after coagulation, there was no change in visual acuity in 13 of 24 eyes in comparison with the preoperative findings. Of them, 9 eyes (37.5%) belonged to the group coagulated with higher energy and 4 eyes (16.7%) to the group coagulated with less in tense spots. In 10 eyes (41.7%), the visual acu ity was found to be worse at this point in time by more than two lines. Three of the eyes (12.5%) were coagulated with high energy and 7 with low energy. After the same time period, 1eye (4.2%) improved by more than two lines; it had been coagulated using low energy.
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Visual Acuity
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Visual Field
Examination of the visual field with the Tübingen Automatic Perimeter showed only minor changes in 5 eyes (20.8%) a few days after coagulation in comparison with the pre operative findings. Of these, 2 eyes (8.3%) were treated with high-energy coagulation and 3 (12.5%) with low energy. In the remaining 19 eyes (79.2%), more or less pronounced scoto ma was detected. Of these, 10 eyes (41.7%) had been coagulated with high energy and 9 (37.5%) with low energy. Twelve months after coagulation, 13 eyes (54.2%) were found to show no or little change in comparison with the preoperative findings. Of these, 5 eyes (20.8%) had been coagulated with high-energy coagulation spots and 8 with low-energy spots. Eleven eyes (45.8%) showed clear-cut worsening of the visual field: 8 eyes (33.3%) belonging to the group coagulated with high energy and 4 (16.7%) to the group receiving low energy coagulation. With regard to pairs of eyes, in 8 pairs (66.7%), the findings were the same in both eyes after 12 months. In 3 pairs of eyes (25%), the eye coagulated with high energy was found to be significantly worse in comparison with the fellow eye: in 1 pair of eyes (8.3%), the eye treated with less intense spots had worse findings than the fellow eye.
Fig. 2. ERG: mean a- and b-wave. Solid line: highenergy coagulation; dashed line: low-energy coagula tion.
Electroretinography
Preoperatively, clear amplitude differences were demonstrated interindividually in both the a- and b-waves. The mean values of the amplitudes, did not differ significantly in the two groups. The amplitudes were normal in 20 eyes (83.3%) and pathological in 4 eyes (16.7%). Within 3 days after the operation and at later examinations, a clear-cut deterioration of the a- and b-wave was detected. The eyes treated with intense coagulation spots showed slightly lower mean potentials in the a- and b-waves than did eyes coagulated with weaker energy (fig. 2). Electro-Oculography
The mean values of pre- and postoperative potentials as well as the L/D ratio are shown in table 1. The Arden quotient showed an appre ciable coagulation-dependent postoperative reduction in comparison with the preoperative value. The light increase was then hardly rec ognizable. There were no significant differ ences between the two groups (fig. 3). Complications in Coagulation Treatment
All eyes that received fairly strong coag ulation spots proved to be free of complica-
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Fig. 1. Mean visual acuity. Solid line: high-energy coagulation: dashed line: low-energy coagulation.
Function of the Diabetic Retina after Panretinal Argon Laser Photocoagulation
Table 1. EOG: mean values of resting potential and L/D ratio (n = 24) Laser PrcPostoperatively energy operatively < 3 3 6 9 days months Resting potential pV
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High Low
383 402
200 338 215 293
287 313
240 271 260 294
L/D ratio High Low
2.73 2.78
1.42 1.61 1.37 1.74
1.70 1.48 1.35 1.82 1.53 1.31
tions. In contrast, in the group of 12 eyes treat ed with high-energy laser spots, 3 eyes (14.7%) had a small amount of localized choroidal bleeding; in 4 eyes (33.3%) there was small intra- and preretinal bleeding, and in 1 eye (8.3%) there was choroidal detachment. In 1 eye (8.3%) secondary angle closure occurred, which resolved after conservative treatment and a return to normal of the retinal and cho roidal swelling. No operative treatment was required. Postoperative Findings
Twelve months after coagulation, 13 eyes (54.2%) showed no change in comparison with the preoperative situation. Eleven eyes
(45.8%) became worse in the course of the year after coagulation: aneurysms, spot and blot hemorrhages, hard exsudate, chronic retinal edema at the posterior pole, and cystoid mac ular edema were responsible. Of the 11 eyes (45.8%) that had become worse, 3 (12.57%) had been treated with intense coagulation spots and 8 (33.3%) with less intense spots. When comparing eye pairs, 5 pairs (41.7%) showed equal findings in both eyes. In 2 pairs of eyes (16.6%), the eye treated with high-en ergy coagulation showed worse findings; in 5 pairs (41.7%) the eye coagulated with low ener gy showed worse findings.
Discussion Experience to date with laser coagulation supports the assumption that not only the ex tent of the retinal area coagulated but also the volume of coagulation determine the effective ness of this method of treating diabetic reti nopathy. Using the same spot diameter, the volume of coagulation is dependent upon the exposure time and the energy applied. When the effect of the energy is minor, the volume of the coagulation spot after absorp tion of the light energy in the melanin of the retinal pigment epithelium and the uveal mela nocytes is relatively low [17]. In addition to the retinal pigment epithelium, only the exterior layer of the sensory retina is damaged. Only with very high intensity is the nerve fiber layer also involved [13, 45]. More cells in the retina are destroyed by high-energy coagulation due to greater spot volume. Although the receptor layer has a rel atively high requirement for oxygen, the ox ygen requirement in the remaining retina will be lower than in coagulation using less energy; this results in lower spot volume and damage
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Fig. 3. EOG: mean L/D ratio. Solid line: high-ener gy coagulation; dashed line: low-energy coagulation.
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to the receptor layer alone. Since the effect of photocoagulation in diabetic retinopathy is re ached, among others, through improvement in the oxygen supply to the remainder of the reti na, greater therapeutic success would then be expected in coagulation using higher energy. Diffusion of the choroidea into the retina, as can be demonstrated via fluorescence an giography, may have an influence on the course of diabetic retinopathy. Diffusion comes into play if the retinal pigment epitheli um is destroyed as a barrier through intense coagulation [39]. In the same way, after high-energy photo coagulation, the neovascularization extending from the choroid ruptures Bruch's membrane and the pigment epithelium in the direction of the retina. These new vessel formations may also have an effect on the pathological metabol ic processes that occur in diabetes mellitus [8], Thus there are some reasons for applying relatively high-energy coagulation spots in dis seminated coagulation for the treatment of diabetic retinopathy. Such intense spots may be achieved by extending the exposure time or increasing the energy used. The influence of exposure time on the clin ical course in patients with proliferative diabet ic retinopathy has already been investigated by Meyer-Schwickerath et al. [34]. In their results the variable effects of different coagulation techniques were attributed solely to a longer exposure time. In reality, however, coagula tion spots with varying exposure times and dif ferent intensities were compared. A more fa vorable course was observed in eyes that were coagulated with a longer exposure time and therefore greater energy. If the application time is kept constant, the true influence of applying different energy lev els can be investigated. The goal of our pro spective study was therefore to investigate the
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course of the retinopathy and retinal function under these given conditions. If a clear-cut difference in energy is selected using equal exposure times and an identical laser beam diameter, the diameter of the re sulting coagulation spot is greater. This, in turn, influences individual retinal function tests [43]. For this reason, we chose a smaller laser beam diameter for coagulation with greater energy in order to balance the diame ter of the spots created. After laser coagulation for diabetic retinop athy, a lasting reduction in visual acuity often occurs: the incidence is given as between 3 and 25.2% [9, 26, 32, 43]. Our investigation showed that in the following days after the operation a decrease in visual acuity occurred less often in the group coagulated with intense spots than in the group of eyes coagulated with moderate spots, although one could expect more pronounced coagulation-dependent ede ma, which is the cause of the decrease in visual function. After 1 year, visual acuity deteriorat ed less frequently in the group of eyes treated with high-energy spots. A variable amount of visual field loss is often found in diabetic retinopathy, and the extent of the loss depends on the severity of the illness [1. 2, 7, 16, 21, 40, 46, 48]. After panretinal laser coagulation, prolonged additional scotoma can be detected in some patients [1,2,7,16,20,43]. In the present investigation, this was also ver ified by means of computed static perimetry. When comparing the two coagulation methods, no differences in the degree of functional dis turbance could be determined a few days after treatment. However, after the coagulationcaused edema in the retina had receded in the course of months and only the scar-caused sco toma could be detected, 1 year postoperatively heavily coagulated eyes showed appreciably more loss in visual field than the fellow eyes.
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In diabetic retinopathy, the amplitudes of the a- and b-waves of the ERG have been de scribed as normal [25,38,47] or as reduced [15, 19,27,36]. After panretinal photocoagulation, the ERG is permanently reduced [2, 7, 15, 25, 27, 36, 38]. In our patients, the preoperative amplitudes were normal in 20 eyes (83.3%) and pathological in 4 eyes (16.7%). After treat ment, when the mean a- and b-wave potentials were much lower than before treatment, the a-wave potential was shown to be compara tively smaller in eyes coagulated with highenergy laser spots. This difference is even clearer in the potentials of the b-wave. These results show that more severe damage occurs in the middle retinal layers with the use of high-energy coagulation. In eyes with diabetic retinopathy, the rest ing potential and Arden quotient of the EOG are reduced in relationship to the severity of the disease [4, 7, 19, 23, 42]. Also, in our pa tients the resting potential was preoperatively found to be pathological in 5 eyes (20.8%). Postoperatively in 2 eyes (8.3%), the L/D ratio was hardly reduced at the beginning, which has been established by other authors as well [4, 7, 42]. They also found that this parameter shows a certain amount of recovery in the course of months [43], a finding verfied in the present investigation. The two coagulation methods showed no differences. This is an indication that the calculated and actual surfaces of the damaged pigment epithelium are almost the same in both eyes of a given patient. The transient complications caused by laser coagulation can be multiple [20,22,28,49] and the complication rate depends on the amount of energy used. Small retinal and choroidal hemorrhages, choroidal detachment, and sec ondary angle closure only occurred in our pa tients if they had been treated with intense spots.
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Also, the repair processes of the retina after photocoagulation are energy dependent. The use of moderately intense spots produces full thickness defects in the retina, in which appar ently firm retinal adhesions arise. However, the use of very strong coagulation leads to the retina losing its ability to form glial scars. The retinal pigment epithelium is then only source of the retinal repair process. When such in tense spots are used, preretinal glial mem branes can often be observed that have a tan gential pulling effect on the retina [45]. In the present study, the number of eyes investigated was small. Nevertheless, the hy potheses appear to have been confirmed due to our findings that strong coagulation spots are advantageous in the clinical course of dia betic retinopathy even if visual field loss occurs appreciably more often 1year later than in eyes coagulated with less intense spots. Early coag ulation complication such as hemorrhages in the retina and choroid and angle closure, as well as late complications with the formation of preretinal, glial membranes with a pulling effect, occur only after very high-energy coag ulation. Even so, when eyes with diabetic reti nopathy are coagulated with intense spots, they are less likely to deteriorate, at a later time, than the fellow eye. For these complica tions, very-high-energy coagulation with a rel atively short exposure time does not appear to be indicated. This is the reason why we did not extend our study to include a large number of patients and why we do not recommend coag ulation with very intense spots even though theoretical considerations indicate that this form of coagulation might be quite advanta geous. Instead, the spots should be smaller [43] and of average energy, as demonstrated by the results to date which, however, arc not significant on account of the small number of patients.
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Function of the Diabetic Retina after Panretinal Argon Laser Photocoagulation
Acknowledgement We thank Ms. U. Schibel for her help with the electrophysiological findings.
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Received: August 27,1990 Accepted: September 10,1990 Dr. med. Volker Seiberth Universitäts- Augenklinik Direktor: Prof. Dr. med. H. Liesenhoff Klinikum Mannheim Fakultät für Klinische Medizin der Universität Heidelberg Theodor-Kutzer-Ufer D-W-6800 Mannheim (FRG)
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