Retinal laser photocoagulation: Benefits and risks

RETINAL

LASER PHOTOCOAGULATION: BENEFITS AND RISKS ROHER~ N. FRANR

The kwgc

Wayne State IJnl\erslty

F->e Institute,

School

of Medicine.

Detroit.

MI

4X201. I’ S A

Abstract

Rctlnal photocoagulation has been u\ed for approximately 20 yr to treat a number of diacaw rarcl>

sia may be given. Use of such anesthesia

I use it only infrequent&.

dual matter: photouoapulntlot1

Kctinal

was introduced

of the xenon arc photocoagulator

with the use

by Meyer- Schwick-

erath in the 1950’s. hut after the development It became eLident advantages

that rhcse devices might

for ophthalmic

type> of Iascrs ha\r including Watzhe

t’l

t/l..

;IIICC.

1974).

Q-switched ~hle

laser (Beetham the

1971: Schulenberg

duce extremel) aids

though

to

the)

ha\c

not t;nmd

laser for rctrnal tinuous

flow

therap!

of water.

unit5

lamp.

ho that

fundu\

through

rected

anti

lens.

the pulse. it> diameter.

lntcnstties

to an ophthalmic system with

of the retina vary

bq hand the laser

i, now almost procedure.

are applied.

always

Particularly

or

when

widely

from

simply

cannot

apphcations

in rn!

patient tolerate

of

to

own

experience

patient.

When

the treatment.

perwhen

very

YI-c used. there may be some associated although

the

the energy

high

eqc movtments

burn with permanent

the

cvcr!

has been employed

risks. at least over

a good

the short

and. for

the most

I shall describe them m detail

mild.

and radioisotopes

be no such dangers lengths

much as the earl\

longusers of

did not foresee the delayed Theoretically,

in retinal

employed

are

there should

laser those

trcatmcnt. of

\Ghlc

pourr

The penetrating

of laser beams as used in ophthalmic

therapy

and all of the energy that traverses

the optically

media of the eye is absorbed the retina. sensory

the retina.

or by the blood

histologic

is cell death,

Finally.

and

retinal

transformation.

unlike

effect

those organs a relatively

Nevertheless.

believe the risk is small. we should placent.

and

ocular

patients

who

should

examinations

have

undergo

and

malignant

nh1c.11

in

which are also organs with tumors.

heen

cpithelium

never undergo

of

laser therapy

has

the cells of the ncuro-

cancers are most commonly

spontaneous

clear struc-

bcssels of

that

pigment

vessels Lirtually

tion-induced

13 small.

by the pigmented

The only

retina

The light.

by nucleic acids and thcrcforr

not cause mutagenesis.

tures just behind

deal term.

radia-

observed

high Incidence

I

although

not become comundergone

careful

and

retinal frcqurnt

for many years to come

dis-

patient

or when

I place this

laser

may result in a fovea1

visual loss. retrobulbar

virtually

this varies

must he made very close to the fovea. so

that Inadvertent

treatment

dangers of carcinogenesis.

their blood

an11 duration,

outpatient burns

slit

the patient’s

to

We of course have no idea of potential

observed

the laser beam can be di-

controls

laser treatment

[IL; ;UI

with a

laser that

i\ used to trigger

hand

is

of the currently

can view

rcglons

Gtch

pulse. and suitable

laser

Most

the slit lamp optical

A foot

Retinal

unit,

below.

wave

it

laser therapq

these are infrequent

relaticely

should

as a con-

cooling

laser

which are not absorbed

of retinal

laser. which both

as a pulsed

arc connected

at appropriate

controls.

comfort.

and

the phy\rcian

aid of a cnntact

many

is the argon

no water cooling

available

al-

titne. by far the most popular

by \a~-lous manufacturers.

give

10 years, we have learned

its possible

X-ray

as poss1973).

retinal

Fortunately. part.

to

term risks of laser therapy.

wide use in this country.

wave laser whohe tube requires

requires

formed

(Krasnov.

uhcd for the treatment

disease. At the present

constant

laser

laser (L’Esper-

pulses. such as the

therapy

and they arc nowhere

produced.

disease.

c’f trl.. 1979). Lasers that pro-

glaucoma

Since about

(“I ul.. 1970:

laser. have been investigated

prefer

who comes for retinal

now for over

different

neodymium-YAG

brief. high-energy

rub!

of lasers

Several

1971) and the krypton

patient

have many

hccn used to treat retinal

the pulsed ruby

(L‘Esperance.

therapy.

thalmologists

15 an indlvi-

but some oph-

anesthe-

section

first.

risks. because at present laser therapy. mously

although

impressive.

still limited and

hazards. The demonstration 1073

before

the discussion

the documented far

benctits

of of

in scope. are enor-

outweigh

the

known

of these benefit< is one 01

1074

ROR~KIN.

the outstanding success stories m the history of ophthalmology. It was evident from the trme when retinal photocoagulation was introduced that this modality might be well suited for the treatment of retinal and choroidal vascular diseases. One could simply focus the intense light beam on the abnormal vascular formations and. provided’the light energy was of an appropriate wave length to be absorbed by hemoglobin. one should be able to coagulate the vessels. Problems arose if the vessels were located on the optic disc, or were elevated above the surface of the retina. or were located too close to the fovea since (particularly with the xenon photocoagulator. which produces a relatively large burn diameter and relatively low beam energy) the hazards of damage to the optic nerve LX the fovea1 retina in these situations were great. and it appeared difficult to destroy highly elevated vessels in this way. Nevertheless. treatment of several different retinal diseases .by photocoagulation. either with the xenon arc or various lasers. was reported enthusiastically (Zweng t’r ctl.. 1969; Okun t’r nl.. 1971). However, a number of clinicians were more guarded in their optimism (Irvine and Norton. 1971). They pointed out that many retinal and choroidal vascular diseases, including diabetic retinopathy. were not invariably destructive. and that spontaneous remissions did occur. Therefore. in order to determine if the new therapy was beneficial. a carefully constructed, large scale. randomized controlled clinical trial had to be organized. In addition. several investigators questioned if the obvious treatment method, direct photocoagulation of abnormal vascular formations, was actually the most effective. particularly for those vascular lesions located on the optic disc and near the fovea. where even with the more adaptable laser instruments. they remained difficult to treat directly. Based on a series of clinical observations. they suggested a new method of applying photocoagulation treatment. by extensive placement of multiple xenon or laser burns over most of the retina outside of the macular regiona. Results with this method. which has been called “panretinal photocoagulation” (PRP). were first described on a large series of patients with proliferative diabetic retinopathy by Beetham t’t ul. (1970). A beneficial effect was apparent. Impressively, Beetham and his colleagues used the pulsed ruby laser for their treatments. This instrument produces deep red light (i = 693nm) which is not absorbed by hemoglobin, but only by the melanin pigment of the retinal pigment epithelium and choroid. Thus. direct laser treatment of abnormal retinal vessels was impossible with PRP as Beetham rr d. used it. Encouraged by these preliminary results, and stimulated by the evident need to develop a large controlled clinical trial of retinal photocoagulation for proliferative diabetic retinopathy. the most common and serious of the retinal vascular diseases, a group of ophthalmologists, supported by the National Eye Institute. developed the Diabetic Retinopathy Study

FRANK

(DRS). a program that eventually involved over 1700 patients and 15 participating centers. Recruitment for the program was limited to patients with bilateral proliferative retinopathy (later modified to unilateral proliferative disease with severe nonproliferative disease in the fellow eye) and visual acuny of 2OJoO (6130. or 0.2) or better in each eye. Other exclusion criteria included age over 70, recent intraocular surgery or photocoagulation, and systemic health sufficiently poor that 5-yr survival (the expected duration of the study) was questionable. Treatment was randomly allocated to argon laser or xenon arc photocoagulation to one eye, which was also chosen at random. The treatment modality was panretinal photocoagulation. together with focal photocoagulation to flat networks of new vessels not located on or near the optic disc, As defined for this protocol. panretinal photocoagulation means the placement of X00- I200 laser lesions of moderate intensity, StNI~rn in diameter and spaced one-half burn diameter apart over the entire retina out to the equator. The lesions are placed outside the superior and inferior temporal vascular arcades, nasal to the optic disc. and outside a vertical line between the temporal vascular arcades and two disc diameters temporal to the fovea (Fig. I). For the new Early Treatment Diabetic Retinopathy Study protocol, the number of laser lesions has been increased to 1200-1600 for a complete course of treatment. For argon laser treatment, photocoagulation of elevated new vessels, or those located on the optic disc. were optional in the DRS The endpoint of the DRS study was defined as a reduction m best-corrected vision of an eye to 51200 or less (6’240 or 0.025) recorded at two successive clinic visits ,tt intervals of 4 months. After many patients had been followed for only 3 yr. the DRS had already produced impressive results. demonstrating an unequivocal benefit of panretinal photocoagulation, either with the xenon arc or the argon laser. in the treatment of proliferative diabetic retinopathy (Diabetic Retinopathy Study Research Group, 1976, 1978, 1979). After 3 yr of follow-up. progression to the endpoint had occurred in nearly 30”; of untreated eyes. but in only about lo”.,, of treated eyes, a difference that was statistically highly significant (DRS Research Group, 1976, 1978). Eyes with certain abnormalities were considered to be at particularly high risk for visual loss within 3 yr. and hence were considered especially strong candidates for photocoagulation treatment according to the study protocol. These included : (I) Eyes with mild new vessels on the optic disc (NVD) together with vitreous or preretinal hemorrhage or both; (2) Eyes with moderate or severe NVD without vitreous or preretinal hemorrhage; (3) Eyes wrth moderate or severe NVD with vitreous or preretinal hemorrhage or both; and (4) Eyes with moderate or severe new vessels “elsewhere” (NVE), i.e. at least one disc diameter away from the disc, together with vitreous or preretinal hemorrhage or both. “Mild.” “moderate.”

Retinal

laser photocoagulation:

or “severe” NVD are defined as a neovascular formation equal to or greater than one-half disc area in extent on a single photographic field. The DRS results have been confirmed by a smaller study, the British Multicentre Photocoagulation Trial. conducted in Great Britain and Norway (British Multicentre Photocoagulation Trial, 1977: C’heng. 1976). This latter study. however, used the xenon arc coagulator exclusively. The beneficial effects of panretinal photocoagulation exemplify the fact that empirical observation may sometimes lead to progress in advance of theory and basic investigation. An explanation for the success of this mode of treatment is still lacking. The most widely cited current hypothesis holds that large areas of the diabetic retina become hypoxic as a result of nonperfusion of retinal capillaries due to disease of their component vascular cells. The hypoxic retina liberates an angiogenic stimulus that leads to the development of abnormal new vessels. By destroying large areas of hypoxic retina. panretinal photocoagulation is thought to reduce the formation of the presumptive angiogenic factor. Attempts to verify this hypothesis now occupy several laboratory groups around the United States. Although the DRS results for proliferative diabetic retinopathy remain the most impressive documentation of the therapeutic effectiveness of retinal laser therapy. lasers and other photocoagulators have been used to treat numerous other retinal disorders. Treatment of background diabetic retinopathy by photocoagulation has been widely employed. Here. the strategy is to localize and destroy by coagulation microaneurysms and other vascular formations in the macular region that are “leaky,” as demonstrated either by fluorescein angiography or by the fact that they lie in the center of rings of lipid exudate. Focal treatment of these vascular lesions. it is thought, may prevent transudation or exudation of fluid from the vessels and thereby retard the progression of macular edema with preservation of central vision. Two randomized. controlled clinical trials of photocoagulation for macular edema have been reported (Patz c’t ul.. 1973; British Multicentre Photocoagulation Trial. 1975). Each describe beneficial effects of treatment. but the benefit+ although statistically significant -was slight. Over the follow-up periods reported. which were not longer than 3 yr in either study, treated eyes on the average suffered less visual decline than did untreated eyes. with the mean difference in visual acuity being roughtly one line on a Snellen chart. Since these results are by no means definitive, a much larger study of this problem has been designed and began recruiting patients in early 1980. This is the Early Treatment Diabetic Retinopathy Study (ETDRS). funded by the National Eye Institute and including 20 clinics in the United States and Puerto Rico. At least 4000 patients are expected to be recruited, either with diabetic macular edema or “preproliferative” retinopathy. Argon laser treatment

benefits

and risks

I075

by one of four specified protocols. chosen at random. will be given to one eye. selected at random. with the fellow eye serving as control. Finally, since there is interest in medical therapy to forestall the progression of diabetic retinopathy. patients will be randomly assigned to aspirin treatment or placebo groups. The rationale for this therapy is that abnormally increased platelet aggregation. which is Inhibited by aspirin. is often present in diabetics and is thought hv some to play a causal role in diabetic retinopathy. Still another disorder for which there IS evtdence of benefit from retinal laser photocoagulatton 15 neovascular glaucoma. In this condition, which may develop as a sequel to diabetic retinopathy or to central retinal vein occlusion. abnormal new blood vessels form on the surface of the iris and. accompanied hy a connective tissue membrane. invade the anterior chamber angle. reducing the efflux of aqueous humor. The glaucoma which results produces massive elevations of intraocular pressure. severe pain and irreversible visual loss. Three relatively small-scale randomized. controlled clinical trials have been reported (Little (‘I ul., 1976: May er trl.. 1976: Wand 01 ‘rl.. 1978) that describe either reversal of the glaucomatous process or. in eyes treated shortly after the occurrence of ccntral retinal vsein occlusion. prevention of its development in significantly more of the treated eyes than of the controls. The treatment protocol was panretinal photocoagulation. similar to that used in the Diabetic Retinopathy Study The mechanism bv which this “indirect” application of laser treatment to the rc~irrtr inhibits neovascular growth on the iri\ I\ obscure. Again. hypotheses about a diffusible “angiogcnesi< factor,” produced in ischemic retina. but which can diffuse forward to produce new vessels in the anterior ocular segment. are currently most popular. Several other retinal vascular diseases in which new vessel formation or macular edema produce visual loss have also been treated by the laser. hut definitive evidence of beneticial effects has not appeared These include retinal branch vein occlusions. sickle cell retinopathy. and chronic retinal vascular and uv,eal inflammations. A cooperative chmcal trial Involving six institutions is now underway to test the cllicacy of laser treatment for branch vein occlusions ((‘larkson et al.. 1979). ais is a study involving two instituttonsthe University of Illinois and the University of the West Indies at Kingston. Jamaica- in the treatment of proliferative sickle cell retinopathy. Treatment protocols in these disorders include “scatter” treatment of the involved retinal quadrant for vein occlu\tons (a sort of partial panretinal photocoagulationl. and focal treatment of the peripheral neocascular frcmds in sickle cell retinopathy. A number of disorders that appear to Involve the choroidal circulation initially. and the retma \econdarily. with destruction of macular vision. have also been treated with the laser. In several of these. neovascular networks arising from the choroidal capillaries form beneath the outer retinal layers. In others.

1076

ROBI:IU

Auid apparently dericed from the choroidal circulation collects underneath the retinal pigment epithehum. and may leak into the potential space between the pigment epithelium and the neurosensory retina. causing visual disturbance. Clnfortunately. often the principal lesions in these disorders lie directly beneath the fovea, so that photocoagulation, even if it successfully ablates the lesion. will also irreversibly destroy central vision. Treatment may be attempted in favnrable cases. in which the inciting lesion is extrafoveal in location. However, at least for the diseases that produce subretinal neovascularization. there is no evidence of a beneficial effect. Yet another randomized. controlled. cooperative clinical trial involving several institutions. the Macular Photocoagulation Study, will shortly begin recruiting patients either with senile macular degeneration or with the presumed ocular histoplasmosis syndrome to test the efficacy of laser therapy for these conditions. Finally. one small-scale controlled clinical trial has been published regarding laser treatment for central serous retinopathg. a disorder most common in young males. in which fluid collects under the retinal pigment cpithelium and neural retina (Watzke er (II.. lY74). This condition is usually mild and self-limited. However. Watzkc and his collaborators found that ruby laser treatment. in the form of a few light burns to the surface of the ‘.pigment epithelial detachment” shortened the course of the disturbance. but did nnt appear to impro\,c the tinal visual outcome. Presumably the same result would have been obtained had the argon laser or other photocoagulators been used, Since the disease is so mild and self-limited. and since complications of laser treatment may occur, however infrequently. some clinicians advise non-treatment of central serous retinopathy (Klein u (II.. lY74). My own preference is not to treat unless the visual disturbance is unusually severe or the course unusually prolonged. i.e. more than 6 months in duration. Laser treatment has been used for retinal and choroidal tumors. although once again, there have been an insufficient number of cases. and no controlled trials. Small retinal angiomas may be eradicated by photocoagulation, but larger ones cannot usually be treated successfully in this way, The reasons are. tirst. that the blood flow is rapid through these tumors, and serves as a “heat exchange” to decrease the thermal effect of the absorbed light energy. which is the principal means by which photocoagulation exerts its effect. Second, nearly all of the energy. even for very intense laser beams, is absorbed near the surface of’ the tumor, so that the larger part of a bulky lesion remains undamaged This same point applies for tumors not of blood vessel origin. such as melanomas. which some clinicians have also treated by photocoagulation (e.g. Vogel. 1972). For most ophthalmologists. extirpative surgery remains the treatment of choice for uveal melanomas when a decision is made for treatment rather than observation.

?‘i. i=RANh

Considering the extensiveness of panrctmal photocoagulation treatment (Fig. I). one is surprised that its deleterious effects on vision are 60 slight. The t&o most common sequelae are yrtlr0rli:A . i~~ttkriot~ of rhr cisd jield (Frank. 1975). which I5 &en quite minimal (Fig. 2), and &UVLIS~L/nighr W&HZThe latter probably is related to the fact that ~hc panretinai treatment IS heaciest in the region of titc retina where the rod density is highest. and i\ rcilccted bq the observation that the amplitude of t11~ clcctroretinographic b-wave to a blue stimulus des~pned to elicit a maximal response from the rod system is reduced much more following panretinai photocoagulation than is the b-wave to a red. photopic stimulus (Frank. 1075). In some cases. more scverc lic1i.i drrtlctsarc noted. including large focal scotoma:. nerve fiber layer scotomas, and severe constriGt:on of the field. Peripheral visual field testing was cari led out in the Diabetic Retinopathy Study. using on!! a single. large test object (the IV;4e of the Goldmann perimeter;. This showed that. on the average. peripheral field loss was greater when panretinal photi,coagulation wa’r carried out with the xenon photocoagulator than with the argon laser. Perhaps thib is to 1~ expected. smco the xenon instrument producch .i mtu.3~larger INII-n (Diabetic Retinopathy Stud) Rest:ar:!; (ir~up. 1076. lY78) A major danger of photocoaguiat1irr-i. hug one rhat can be avoided with proper cdrL.. is inadvertent photocoagulation of the fovea with cvrrtral visual loss. The greatest risk is present in treatment of macular diseases, particularly when the lesion :O hc coagulated lies close to the fovea. Two precaurions to avoid this hazard are. first. never to treat with the laser closer than about I25 pm (one major vein-?vitlth at the margin of the optic disc) from the fo\caI avascular zone. and, second. to use retrobulbar onesthrsra for macular treatments when photocoagulation nII\ \vith the laser. focal disc treatment has largeI> been abandoned. One reason is that. following very heavy photocoagulation to extensive NVD. there have been occasional reports of severe ischemic optic neuropath! with irreversible visual loss (Goldberg and Herbst, 1973. Zweng tit ni.. i 974). Perhaps one reason why panretinal photocouguiation is often so little damaging to vision is that photocoagulation lesions of the intensities usually used for these treatments produce their damage primarily in the outer layers of the retina. without touching the

Fig. 1. Montage of the posterior fundus immediately following panretinal argon laser photocoagulation in a patient with proliferative diabetic retinopathy. From, R. N. Frank, Archs Ophthal. 93, 591-598 (1975) by permission of the editors, Archives of Oph~hulmolog~. Copyright 1975, The American Medical Association.

1077

Fig. 3. A sequence of frames from a Ruorescein angiogram of a 56-yr old diabetic man 4 months following panretimd argon laser photocoaguIation and heavy focal photocoagulation for an extensive. elevated frond of retinal neovascularization. Initially, the frond appeared to have been totally destroyed, as demonstrated by an angiogram 2 months after treatment. Subsequently, this new frond appeared. From the sequential photographs. one can see that it fills from the choroidal cimulation. 107x

Retinal laser photocoagulatlon:

I079

benefits and risks

Fig. 2. (A) Pretreatment visual field, obtained with the Goldmann perimeter. of the eye shown m FIB. I (B) Visual field of the same eye nine months after treatment, showing only mild. generalued conslrictlon This is the commonest visual field change following such treatment From. R N. Frank. .4rch~ Ophrhtrl. 93.

591 -598

(1975)

by permission

of the editors. American

cells or nerve fiber layer (Powell 4f rrl.. 1971: Apple et crl.. 1973). However. if focal treatment is applied to preretinal hemorrhages. or to intraretinal vascular lesions. especially within the papillomacular bundle. nerve fiber layer damage may result. This type of treatment. therefore. should usually be avoided. An obvious hazard of photocoagulation treatment. but one which occurs surprisingly infrequently. is the production of hemorrhages either from the retinal or choroidal vessels. Particularly in the course of panretinal treatment it is easy to place a laser burn over a major retinal vessel. Yet. hemorrhage from major

ganglion

Arcl~irr

Medical

(?/ Ophrhulmoloy,~.

Copyright

1975. The

Association.

vessels resulting from photocoagulation is rare. It most frequently occurs following extremely brief (100 msec or less). intense burns of small (5@ lo0 jtm) diameter. and is usually seen in treatment of retinal new vessel formations, or arising from the choroidal vessels. even when these are normal, but lie alongside abnormal retinal vessels that were being photocoagulated. When such a retinal or choroidal hemorrhage occurs during treatment. the empirical remedy is to increase the laser spot size and power and treat directly over the emerging blood to coagulate it thermally and stop the bleeding. Unless the hemorrhage is

IOXU

ROBERTN. FRANK

profuse, this treatment is usually successful. However. in the case of choroidal hemorrhage, the undesirable sequel may be choroidovitreal neovascularization. Galinos c’t ~1. (1975, 1976) have reported the development of extensive fronds of new vessels arising from the choroidal circulation and projecting through the retina into the vitreous or anastamosing with the retinal circulation. following heavy photocoagulation to the area. The stimulus to these unusual neovascular formations (Fig. 3) is unknown, but it is felt that, like choroidal hemorrhages, they result from extremely heavy applications of laser treatment using small spot sizes. Hence, for the focal treatment of many types of retinal neovascular formations, particularly those with large caliber feeding vessels as may often be seen in sickle cell retinopathy, it is now recommended that large (5OO~m) spot sizes be used, with heavy laser applications to coagulate the vessel. Choroidal detachments, usually in the periphery, may be seen within a few days following heavy (panretinal) photocoagulation. Often patients are not aware of them, although vision may be reduced more than is usual at this point after treatment. and the eye is soft. These detachments virtually always resolve spontaneously and require no treatment. In my own experience, choroidal detachments following extensive photocoagulation have occurred primarily in eyes with a history of previous intraocular surgery. The last three that 1 have seen occurred in two patients with prior cataract surgery (one 2 months before laser treatment. and one 10 yr previously) and in one patient with a trabeculectomy done 2 months previously. What the causal relationship is. if any. is unclear. Retinal detachments following laser treatment may be of two kinds. Traction detachments may occur in patients with severe proliferative retinopathy. presumably because, as the vessels atrophy, they and their surrounding fibroglial sheaths contract, pulling off the retina. Therefore. photocoagulation to retinas with extensive traction should be done with great caution. If panretinal photocoagulation is to be carried out in such an eye, I prefer to do it in multiple sessions with only 20&3OO laser burns each. spaced several days apart, While 1 have no evidence that this procedure is better than to carry out the entire treatment all at once, it seems at least intuitively more sensible. The second type of retinal detachment is the rhegrnatogenous variety, due to a hole in the retina. This is much less frequently encountered, and is presumably due to a laser burn of excessive energy that radiates from its site of absorption in the retinal pigment epithelium and choroid through the neural retina, causing extensive destruction and hole formation. Although retinal photocoagulation has been advocated as a means of destroying retinal and choroidal neovascularization, it has occasionally been suggested that such treatment, if it is not heavy enough, may actually stimulute new vessel growth (Frank, 1974: Francois ~‘tal.. 1975) particularly in choroidal lesions.

Conversely, some clinicians (T. Schlaegel. unpublished) have recently advocated partial treatment of choroidal neovascularization that extends underneath the fovea, as a palliative measure. In the absence of controlled studies, it is difficult to decide which of these alternatives is correct Heavy laser coagulation to the retinal periphery for proliferative sickle cell retinopathy has been reported to cause choroidal ischemia (Goldbaum or ~1.. 1976). While this lesion may be impressive ophthalmoscopitally and angiographically. at least in its peripheral location, it appears to cause no clinically detectable functional damage. Heavy photocoagulation in the macular region may cause contraction of the internal limiting membrane of the retina in the macula with decrease in central vision- -so called “macular pucker.” Thi$ occurs most frequently following xenon photocoagulation as demonstrated. perhaps. by the greater prevalence of central visual loss of 2--4 lines after xenon photocoagulation in the DRS than after argon laser treatment (Diabetic Retinopathy Study Research Group, 1976, 1978). For this reason. photocaogulation treatment in or near the macula is preferably carried out with the argon laser instrument. An unusual complication of panretinal photocoagulation is transient ShallOWiIlg d the anterior chamber with compromise of the outllow pathways for aqueous humor and intraocular pressure elevation (Mensher, 1977). These eyes were not felt to be predisposed to angle closure prior to treatment, and following immediate medical treatment. they recovered completely. The patients in whom this complication occurred had all had extensive panretinal photocoagulation with over 1000 laser burns placed at one treatment session. This complication haa not been observed in patients whose panretinal treatment has been divided into two or more sessions. although the causative mechanism remains obscure Finally. although the lens and cornea are normally transparent and do not absorb the photocoagulator beam, certain unusual situations may occur in which a light-absorbing opacity is located adjacent to the lens or cornea with the result thai laser light may cause a thermal burn to these structures. Cornea1 epithelial burns (Ftister er ul., 1971) are usually of little consequence. and will heal rapidly save perhaps in those patients who are susceptible to recurrent corneal erosions. Lens burns may lead to progressive opacities that have the potential to interfere with vision, In summary, photocoagulation therapy with lasers or other instruments may cause a great number of unwanted consequences. However, only a few of these are of serious nature, and these are rare. By contrast, photocoagulation to the retina has a demonstrated, beneficial effect in proliferative diabetic retinopathy, a probable beneficial effect in background diabetic retinopathy and neovascular glaucoma, and there is reason to believe it may be useful in the treatment of

Retinal

laser photocoagulation:

several other retinal and choroidal vascular diseases, By comparison therapies,

with

many

its “risk-benefit

other ratio”

medical

and

is extremely

surgical small.

REFERENCES

Apple D. J.. Goldberg M. F. and Wyhinny G. (1973) Histopathology and ultrastructure of the argon laser lesion in human retinal and choroidal vasculatures. Am. J. Ophrhal. 75. 595-609. Apple D. J., Goldberg M. F. and Wyhinny G. J. (1974) Argon laser treatment of von Hippel-Lindau retinal angiomas. II. Histopathology of treated lesions. Archs Ophthal. 92, 126 130. Beetham W. P.. Aiello L. M.. Balodimos M. C. and Koncz L. (1970) Ruby laser photocoagulation of early diabetic neovascular retinopathy. Archs Ophthal. 83. 261-272. The British Multicentre Photocoagulation Trial (1975) Photocoagulation in the treatment of diabetic maculopathy. Lancer ii, 11CLI 13. The British Multicentre Photocoagulation Trial (1977) Proliferative diabetic retinopathy: treatment with xenonarc photocoagulation. Br. med. J. 1. 739-741. Cheng H. (1976) Response of proliferative diabetic retinopathv to xenon-arc photocoagulation. A multicentre randomized controlled trial: second interim report. Trans. Ophthul. SW. U.K. %, 224-227. Clarkson J.. Diddie K.. Finkelstein D., Orth D.. Trempe C. and the BVOS Group (1979) Branch vein occlusion: the development of a multicenter randomized clinical trial. Itrresf. Ophthul. Vis. Sci. IS. (Suppl.), 181. The Diabetic Retinopathy Study Research Group (1976) Preliminary report on effects of photocoagulation therapy Am. J. Ophthal. 81. 383-396. The Diabetic Retinopathy Study Research Group (1978) Photocoagulation treatment of proliferative diabetic retinopathy: the second report of Diabetic Retinopathy Study findings. Ophrhalntoloyy 85, 82-106. The Diabetic Retinopathy Study Research Group (1979) Four risk factors for severe visual loss from diabetic retinopathy. Archs Ophthal. 97. 654-655. Francois J.. DeLaey J. J.. Cambie E., Hanssens M. and Victoria-Troncoso V. V. (1975) Neovascularization after argon laser photocoagulation of macular lesions. Am. J. Oahthul. 79. 206210. Frank R. N. (1974) Argon laser photocoagulation and subretinal neovascularization. Ophthalmic Surg. 5, 56-64. Frank R. N. (1975) Visual fields and electroretinography following extensive photocoagulation. Archs Ophthal. 93, 591-598 Galmos S. 0.. Asdourian G. K.. Woolf M. B.. Goldberg M. F. and Busse B. J. (1975) Choroido-vitreal neovascularization after argon laser photocoagulation. Arch.7 Ophthal. 93, 524-530. Galinos S. 0.. McMeel J. W., Trempe C. L. and Schepens C. L. (I 976) Chorioretinal. anastamoses after argon laser photocoagulation. Am. J. Ophthal. 82, 241-245. Jampol L.. Woolf M. B. and Busse B. (1976) Acute choroidal ischemia as a complication of photocoagulation. Archs Ophthul. 94. 1025-l 035.

benefits and risks

lOXI

Goldberg M. F. and Herbst R. W. (1973) Acute complications of argon laser photocoagulation. Ar&s Ophrhul. 89.311~318. Goldberg M. F. and Koening S. (1974) Argon laser treatment of von Hippel-Linda; retinal angio-mas. I. Clinical and angiographic findings. Archs Ophthul. 92. I2 I 125. Irvine A. R. and Norton E. W. D. (1971) Photocoagulation of diabetic retinopathy. Am. J. OphthalmoL 71, 437445. Klein M. L.. van Buskirk E. M., Friedman E.. Gragoudas E. and Chandra S. (1974) Experience with nontreatment of central serous choroidopathy. Arr’hs Ophthul. 91. 247-250. Krasnov M. M. (1973) Laseropuncture of anterior chamber angle in glaucoma. Am. J. Ophthul. 75, 674-678. L’Esperance F. A. Jr (1971) Clinical photocoagulation with the frequency doubled neodymium yttrrum-aluminumgarnet laser. Am. J. Ophthol. 71. 631-638. L’Esperance F. A. Jr (1972) Clinical photocoagulation with the krypton laser. Archs Ophfhal. 87, 693-700 Little H. L.. Rosenthal A. R.. Dellaporta A. and Jacobson D. R. (1976) The effect of pan-retinal photocoagulation on rubeosis iridis. Am. J. Ophthal. 81, 8W809. May D. R.. Klein M. L. and Peyman G. A. (1976) A prospective study of xenon arc photocoagulation for central retinal vein occlusion. Br. J. Ophthal. 60, 8 16-81 X. Mensher J. H. (1977) Anterior chamber depth alteration after retinal photocoagulation. Archs Ophthul. 95, 113-116. Okun E.. Johnston G. P. and Boniuk 1. I1971 hMunuuemenr ., of Diabetic, Retinoputhj,’ -4 Strrw.wopi~~ Prtwnturion Mosbv. St. Louis. Patz A..‘Schatz H., Berkow J. W.. Gittelsohn A. M. and Ticho U. (1973) Macular edema-an overlooked comolication of diabetic retinopathy. Truns. .Am. .4cud Ophtkul. Oto-Lur. 77, 0P34-47. Pfister R. R.. Schepens C. L.. Lemp M. A. and Webster R. G. Jr (1971) Photocoagulation keratopathy. 4wh,\ Ophthul. 86. 94-96. Powell J. 0.. Bresnick G. H.. Yanoff M., Frisch G. D. and Chester J. E. (1971) Ocular effects of argon laser radration. II. Histopathology of chorioretinal lesions -1111.J. Ophthal. 71. I267- I276.Schulenbura W. E.. Hamilton .A. M. and Black R. K. (1979) A comparative study of argon laser and krypton laser in the treatment of diabetic optic disc neovascularization. Br. J. Ophthul. 63, 412-417. Vogel M. H. (1972) Treatment of malignant choroidal melanomas with photocoagulation: evaluation of tenyear followup data. Am. J. aphthal. 74, 1 1 I Wand M.. Dueker D. K.. Aiello L. M. and Grant W. M (1978) Effects of panretina) photocoagulation on rubeosis iridis. angle neovascularization. and neovascular glaucoma. Am. J. Ophthal. 86, 332-339. Watzke R. C., Burton T. C. and Leaverton P E. (1974) Ruby laser photocoagulation of central serous retinopathy. Trans. Am. Acurl. Ophthul. Oto-Lur 78, OP205-21 I. Zweng H. C.. Little H. L. and Hammond A. H. (1974) Complications of argon laser photocoagulation. Trans. Am. Acad. Ophrhal. Oto-Lar. 78, OPl95-204 Zweng H. C.. Little H. L. and Peabody R. R. (1969) L~SC,I Photocoagulation and Retinal Angiogruphl,. Mosby. St. Louis.