Documenta Ophthalmologica 44,1 : 81-91, 1977 CONTROVERSIAL ASPECTS OF ABLATIVE PHOTOCOAGULATION IN DIABETIC RETINOPATHY (d.r.)

S. RIASKOFF

(Rotterdam) ABSTRACT In recent years ablative treatment of advanced diabetic retinopathy has gained more and more adherents. However, most cases of proliferative retinopathy, even if they are advanced, can be treated successfully by restricting xenon- or laser-coagulation to pathologic areas, while sparing healthy4ooking parts of the retina. It is felt that destruction of large parts of the retinal periphery should be reserved for special cases only. In those cases where the fundus is clouded by abundant hemorrhages and vitrectomy does not seem advisable, ablative treatment should be tried ab externo by means of diathermy or cryoapplication. ARGUMENTS IN FAVOUR OF ABLATIVE PHOTOCOAGULATION The concept of ablative photocoagulation and its propagation are based on two observations: 1) Ablative photocoagulation has proved to be able to stop or slow down the evolution of proliferative diabetic retinopathy in general (Okun & Johnston, 1968; Wessing & Meyer-Schwickerath, 1968; James & L'Esp6rance, 1974) and especially in those cases with disc neovascularization (Aiello et al., 1968); 2) the results of direct treatment of disc neovascularization with focal or feeder frond coagulation with the argon laser as propagated by Little, Zweng and L'Esp~rance (L'Esp~rance, 1973; Little & Zweng, 1973) did not prove satisfactory, whereas ablative treatment alone or in combination with feeder frond coagulation achieved much better results (Little et al., 1976). Some aspects of the technique of ablative photocoagulation should be considered in order to be able to evaluate this method properly. Most of the ophthalmologists who began to apply photocoagulation to treat d.r. in the early sixties realised that the process could only be stabilised if photocoagulation was apphed very extensively; i.e., when all agglomerations of microaneurysms and exudates, all intraretinal hemorrhages and all newly formed vessels were completely coagulated. The two other important lessons of this early period of photocoagulation were: 1) the treatment proved to be useless in very advanced cases of d.r. as it could not change the course of the disease;

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2) the application of photocoagulation was not well founded in the early stages of d.r. as the natural course of the disease might be benign and the treatment superfluous. The conclusion was: abstain from treatment if you are not sure that the disease is progressive and treat very completely if y o u r are sure that it is. Using the rather large impacts from the Xenon arc coagulator, the destruction was not limited to the lesion but affected the surrounding retinal tissue and the underlying capillaries as well. In cases of advanced retinopathy a great number of coagulates had to be used, implying t h e sacrification of large areas of retinal tissue and a large reduction in the density of the capillary network. We shall not discuss here which of these two effects proved to be the most important but we can conclude that as a result of such treatment the fundoscopic picture o f ' t h e disease became quiescent, often for many years. With the development of laser systems a new vogue arose with tendencies in a somewhat different direction. The greater precision of the laser systems formed a challenge to approach the pathologic lesion more exactly. One could focus on and coagulate a microneurysm without touching the surrounding tissue or obliterate a small vessel within a group of vessels lying close together. Another advantage also seemed quite evident: sitting behind the slitlamp one could avoid the tiresome work of searching through a stenopeic hole for all those lesions so easily found with the fundus contactlens used during laser coagulation. After some positive reports on the treatment of preretinal and prepapillary neovascularization the opinion began to be formed that selective treatment of newly formed vessels was not adequate to solve the problem of neovascularization. Gradually the 'laser men' became aware that the extensive scatter technique had a greater influence on disc neovascularization, even when the newly formed vessels were n o t attacked directly. These observations were explained by the hypothesis of hypoxia. It was assumed that the main symptoms of diabetic retinopathy, capillary leakage and neovascularization, are caused by retinal hypoxia due to a disturbance of the retinal circulation. By destroying hypoxic retinal tissue the .disturbed balance between oxygen need and oxygen supply would be restored to normal, the h y p o x i a would consequently disal~pear and the fundoscopic picture would become quiescent. The conclusion was: to prevent progression of d.r. a pattern of scattered coagulation impacts should be placed around the optic disc and the macular area (Fig. 1). This proposed schematic approach avoided the problem of answering the difficult question of how much retinal tissue should be sacrificed in each case in order to stop the progression of the disease. Ablative therapy, how82

Fig. 1. Pattern of ablative or extensive scatter photocoagulation in diabetic retinopathy.

ever, proved to be beneficial in many cases, especially in proliferative retinopathy. It gradually became popular and nowadays threatens to acquire the fame of being a panacea for all types of d.r. ARGUMENTS AGAINST ABLATIVE PHOTOCOAGULATION In our opinion the pattern of ablative photocoagulation described above should be reserved for special cases. Our arguments against the systematic application of ablative treatment are as follows: Diabetic microangiopathy, which is the underlying cause of d.r., has primarily a multifocal localization. The network of retinal vessels is not involved as a whole and to the same extent at one time. A quite regular sequence of deterioration of different parts of the vascular tree does exist, but we are not able to predict this sequence exactly. It therefore seems preferable to treat only those areas of the retina where pathologic changes

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are seen funduscopically or where they are detectable by means of fluorography or are expected to appear shortly. Areas of presumed future pathology are, for instance: the border zones of cotton wool spots or non-perfused capillaries, the areas around arteriovenous crossings and the streaks along swollen or irregular venous segments. By coagulating only foci of pathologic changes or areas of presumed future pathology we try to prevent the blood supply reaching the damaged parts of the vascular network and to confine it to the still undamaged parts of the retinal vascular system. The proposed focal treatment is, however, not applicable to cases with disc neovascularization. When neovascularization of the disc appears we should a d m i t that there is a circulatory disturbance of the whole vascular system of the retina. In such cases the coagulation of disc neovascularization is not sufficient. More extensive coagulation is obligatory to rectify the circulatory disturbance. Since not all cases of disc neovascularization are identical, the application of a standard pattern of treatment, as proposed

Fig. 2. Pattern of focal and paravenous photocoagulation in diabetic retinopathy with peripheral pathologic changes and neovaseularization on the disc.

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in the case of ablative coagulation, cannot be accepted as a satisfactory procedure. In our opinion there is a risk of overdoing it with ablative coagulation in a great n u m b e r of cases. In order to avoid excessive treatment it seems to us that it is more appropriate to treat cases as follows: a) In cases with neovascularization of the disc and other areas: coagulate all peripheral pathologic changes and also stradle the veins with photocoagulation (Fig. 2). b) In cases where neovascularization is confined to the disc, coagulate along the veins only (Fig. 3). c) If this treatment has had no definite effect on the disc neovascularization within 3 to 5 months, it should be supplemented by ablative coagulation. d) In cases of very advanced proliferative retinopathy and widespread obliteration of arterial branches neither paravenous nor ablative coagulation seems to be able to change the course of the disease. In such cases coaguhation should be confined to areas with newly formed vessels which have led

Fig. 3. Pattern of paravenous photocoagulation in diabetic retinopathy with neovascularization on the disc only.

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to hemorrhage or which are susceptible to hemorrhage'in the further course of the disease. JUSTIFICATION OF PARAVENOUS TREATMENT Our recommendation t o start with paravenous coagulation is based on the fact that in many cases it has proved to be sufficient (Figs. 4, 5, 6). We believe that paravenous coagulation has a specific hemodynamic effect on the retinal circulation. In d.r. a remoulding process occurs in the capillary network in the borderzones of capillary closure. The capillary loops which have lost their connections with the precapillary arteries may be perfused from the wrong venous end and the direction of blood flow may be reversed. This can lead to the dilatation and stretching of the capillary loops around the nonperfused area. To correct the established circulatory problem we have to coagulate mainly those parts of the venous capillary network which correspond to the closed arterial parts (Fig. 7). Fluorography is the best method to determine which areas should be coagulated and which can be spared. Since complete screening of a diabetic retina is quite difficult with this method and in many cases impossible, we prefer to place the coagulation impacts close to the veins, instead of placing them at random between the arteries and veins. It is our opinion that in this way we have the greatest chance of overcoming the circulatory problem

Fig. 4 -Left. Righti eye of a 47-year-old man with neovascularization on the disc only before paravenous photocoagulation. Fig. 4-Right. Same case, 3 months after treatment. The newly formed vessels are partly obliterated and partly embedded in fibrous tissue. 86

Fig. 5 - L e f t . Left eye of a 52-year-old woman with neovascularization on the disc only before paravenous photocoagulation. Fig. 5 Right. Same case, 3 months after treatment. The newly formed vessels are partly obliterated and partly embedded in fibrous tissue.

caused b y closure o f p r e c a p i l l a r y arteries w i t h o u t d a m a g i n g t h o s e p a r t s of t h e r e t i n a l tissue a n d retinal capillaries t h a t are still f u n c t i o n i n g well. We m a y also p r e s u m e t h a t t h e very m u c h n a r r o w e d p r e c a p i l l a r y arterioles in d i a b e t i c p a t i e n t s are n o t able to p e r f u s e t h e very t h i c k a n d dense capillary

Fig. 6 - L e f t . Right eye of a 28-year-old woman with neovascularization on the disc and elsewhere before focal and paravenous treatment. Note preretinal hemorrhages. Fig. 6 -Right.

Same case, 4 years after treatment. Neovascularization has disappeared.

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Fig. 7. Schematic representation of capillary changes in the borderzone of a nonperfused area. By photoeoagulation of this borderzone we may prevent the development of neovascularization.

network of the retina.. It seems logical to us that by destroying part of this capillary network the circulation will be facilitated by simplifying the conneetion between arteries and veins. F o r this purpose the larger coagulation impacts seem more appropriate than the smaller ones (Fig. 8). When this is carried out, we carefully avoid the venous branches which will assure a sufficient connection between arteries and veins (Fig. 9). Instead of flowing through the quite complicated labyrinth of the whole capillary bed the bloodstream will use preferential vessels which have remained open after the destructive coagulation t r e a t m e n t ( F i g . 10). Since the preferential paths represent a shorter connection between arteries and veins, it is presumed that the pressure gradient of the blood flow becomes steeper and consequently the blood flow increases. An accelerated flow of blood in the veins may facilitate the discharge of blood from the newly formed 88

Fig. 8. Schematic representation of the retina with a threeqayered capillary network. Compare the extent of the small and the large coagulation impacts. The small one does not reach the capillaries.

vascular fronds into the veins to which they are connected and may finally lead to their disappearance. We cannot yet prove the above hypothesis on the hemodynamic effects of photocoagulation. The changes in velocity of blood flow may be so slight that the present techniques of clinical fluorography with the usual frequency of photographic recording are not able to demonstrate them. It is however quite certain that with photocoagulation we not only destroy retinal tissue but reduce the capillary network of the retina as well. Therefore, we should start our destructive work in those areas where the circulation in the capillaries is most sluggish and where the density of the capillary network is greatest. These areas are located along the veins. Ablative photocoagulation should be reserved for those cases in which paravenous and focal treatment of peripheral changes has not been able to control the progressive course of the disease. Finally, we shall mention another technique of extensive 'destructive treatment', the effect of which may be compared to ablative coagulation. This is diathermic coagulation via the sclera, introduced by Amalric as full thick-

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Fig. 9. Schematic representation of the capillary network between arteries and veins with coagulation impacts between the small venous tributaries. ness scleral coagulation and modified by Wessing (1971) as lamellar scleral coagulation. This technique is indicated in cases with massive vitreous hemorrhages in

Fig. 10. Schematic representation of the coagulation effect on the capillary network with reduction of its density on the venous side.

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which photocoagulation is impossible and the bl0od does not resorb spontaneously within six months. In order to relax the posterior vitreous membrane and the traction exerted by it on the adherent proliferative retinal strands the lamellar sclera-diathermy is combined with a buckling (scleral indentation) procedure. For this purpose a strip of donor sclera is introduced into the scleral pocket, after which the pocket incision is closed with tightly knotted U sutures. The results of this ab externo alternative to extensive scatter photocoagulation are very satisfying in many cases. The vitreous often clarifies within a few months. Less rubeosis of the iris and less hemorrhagic glaucoma are seen and the tendency to recurrent hemorrhages is diminished. This treatment does not interfere with an eventual vitrectomy. It may even improve the chance of the intra-ocular space remaining transparent after a successful vitrectomy. REFERENCES Aiello, L.M. et al. Ruby laser photocoagulation in treatment of diabetic proliferating retinopathy; preliminary report. In: Symposium on the treatment of diabetic retinoparlay; ed. by M.F. Goldberg & S.L. Fine, p. 437. U.S. Department of Health, Education and Welfare, Virginia (1968). James, W.A. & F.A. L'Espgrance. Treatment of diabetic optic nerve neovascularization by extensive retinal photocoagulation. Amer. J. Ophthal. 78:939-947 (1974). L'Esp~rance, F.A. Argon laser photocoagulation of diabetic retinal neovascularization. (A five year appraisal). Trans. Amer. Acad. OphthaL Otolaryng. 7 7 : 6 - 2 4 (1973). Little, H.L. & H.C. Zweng. Argon laser photocoagulation of disc neovascularization in diabetic retinopathy. Trans. Pac. Coast Otoophthalmol. Soc. 54:123 (1973). Little, H.L. et al. Techniques of argon laser photocoagulatlon of diabetic disk new vessels. Amer. J. OphthaL 82:675-683 (1976). Okun, E. & G.P. Johnston. Role of photocoagulation in the treatment of proliferative diabetic retinopathy: continuation and follow-up studies (359 eyes of 238 patients). In: Symposium on treatment of diabetic retinopathy; ed. by M.F. Goldberg & S.L. Fine, p. 437. U.S. Department of Health, Education and Welfare, Virginia (1968). Wessing, A. & G. Meyer-Schwickerath. Results of photocoagulatlon in diabetic retinopathy. In: Symposium on treatment of diabetic retinopathy; ed. by M.F. Goldberg & S.L. Fine, p. 569. U.S. Department of Health, Education and Welfare, Virginia, (1968). Wessing,A. & I. B6ckenhoff. Die Behandlung der Retinop_athiadiabetica proliferans mit Diathermiekoagulation. Klin. MbL Augenheilk. 158: 212-220 (1971). Author's address: Department of Ophthalmology Eye Clinic Erasmus University Sehiedamse Vest 180 Rotterdam The Netherlands

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Controversial aspects of ablative photocoagulation in diabetic retinopathy (d.r).

Documenta Ophthalmologica 44,1 : 81-91, 1977 CONTROVERSIAL ASPECTS OF ABLATIVE PHOTOCOAGULATION IN DIABETIC RETINOPATHY (d.r.) S. RIASKOFF (Rotterda...
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