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Long-term Efficacy of Argon Laser Trabeculoplasty
Long-term Efficacy of Argon Laser Trabeculoplasty BRADFORD J. SHINGLETON, MD,* CLAUDIA U. RICHTER, MD,* A. ROBERT BELLOWS, MD,* B. THOMAS HUTCHINSON, MD,* ROBERT J. GLYNN, PhD, ScDt
Abstract: Long-term efficacy of 360° argon laser trabeculoplasty was studied in 118 eyes of 93 patients with uncontrolled chronic open-angle glaucoma. The mean intraocular pressure (lOP) decrease was 8.9 ± 5.4 mmHg (mean ± standard deviation [SO] in 71 eyes at 1 year, 9.3 ± 4.3 mmHg (mean ± SD) in 51 eyes at 3 years, and 10.3 ± 3.9 mmHg (mean ± SD) in 28 eyes at 5 years. The probability of success at 4 years (decrease in lOP~ 3 mmHg, lOP :s; 19 mmHg, stable visual field, stable optic nerve, and no further laser or surgical intervention) was 52%. Pretreatment lOP, diagnosis, previous operations, age, and sex were not significant determinants for success or failure. Eyes receiving argon laser trabeculoplasty before cataract surgery maintained control of lOP after surgery. Failure was most common in the first year after treatment (23%), and thereafter failure occurred at a rate of 7 to 10% per year. [Key words: argon laser trabeculoplasty, cataract surgery, filtration surgery, intraocular pressure, Kaplan-Meier survival analysis, optic nerve, primary open-angle glaucoma, proportional hazards model, pseudoexfoliation, visual field.] Ophthalmol qy 94:1513-1518, 1987
Argon laser trabeculoplasty has become an integral part of the ophthalmologist's program for the treatment of open-angle glaucoma. It is a relatively safe outpatient procedure, well tolerated by patients, and has been reported1-3 to lower intraocular pressure (lOP) sufficiently to postpone or prevent glaucoma surgery in 82 to 97% of patients followed from 6 to 24 months. However, concern remains about its long-term effectiveness. Reports with follow-up extending from 1 to 5 years 4 - 7 claim varying success rates from 46 to 94%. This study was designed to further evaluate the long-term efficacy of argon laser trabeculoplasty in controlling lOP, preventing glaucomatous visual loss, and avoiding further laser or surgical intervention in open-angle glaucoma patients.
of
From the Glaucoma SeNice,* Ophthalmic Consultants Boston, Inc, the Glaucoma Consultation SeNice and Epidemiology Unit,t Massachusetts Eye and Ear Infirmary, and the Department of Ophthalmology, HaNard Medical School, Boston. Presented at the American Academy of Ophthalmology Annual Meeting, New Orleans, November 1986.' Reprint requests to Bradford J. Shingleton, MD, Ophthalmic Consultants of Boston, Inc, 50 Staniford Street, Boston, MA 02114.
MATERIALS AND METHODS This retrospective study reviewed 118 eyes of93 consecutive patients with chronic open-angle glaucoma and pseudoexfoliation glaucoma treated by argon laser trabeculoplasty between October 1979 and June 1981. The results in the two eyes in 23 of25 patients treated bilaterally were identical and indicated a high degree of association between the response in fellow eyes. As an analysis which considers pairs of eyes from the same individual as independent observations may be inappropriate, 8 only one of a pair of eyes, randomly selected, was analyzed. The mean age of the 93 patients included in the study was 69.5 ± 8.2 years (mean± standard deviation [SD]) (range, 50-93 years). Fifty-eight percent of the patients were women, 95% were white. Seventy-six eyes had primary open-angle glaucoma, 11 had pseudoexfoliation glaucoma, and 6 had pre-laser lOPs ofless than or equal to 19 mmHg. Patients with other types of secondary open-angle glaucoma, angle-closure glaucoma, and congenital glaucoma were excluded. Sixteen of the eyes with primary open-angle glaucoma had undergone previous surgery (5 eyes had cataract surgery, 4 had filtration 1513
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Table 1. Mean lOPs after Argon Laser Trabeculoplasty Mo of Follow-up Pre-argon laser trabeculoplasty, baseline
1 6 12 18 24 30 36 42 48 54 60
lOP
=
lOP (mmHg) (mean± SO)
No. of Eyes
26.1 ± 18.5 ± 17.0 ± 17.0 ± 18.4 ± 16.8 ± 18.1 ± 16.4 ± 18.5 ± 16.8 ± 16.7 ± 15.4 ±
93 92 75 71 43 61 40 51 34 45 32 28
intraocular pressure; SO
=
5.5 6.2 5.0 4.8 4.4 3.5 3.8 3.6 4.7 4.4 4.8 3.4
Change in lOP (mean± SO)
-7.7 ± 6.4 -8.9 ± 5.4 -8.7 ± 4.6 -9.3 ± 4.3 -8.8 ± 5.5 -10.3 ± 3.9
standard deviation.
had combined cataract and filtration surgery, and 2 had peripheral iridectomies). All patients had either advanced glaucomatous optic nerve damage or significant lOP elevation and would have been candidates for filtration surgery before the introduction of argon laser trabeculoplasty. All patients were maintained on a maximally tolerated medical program for glaucoma control. Glaucoma medications used before argon laser trabeculoplasty included one or more of the following types: topical beta-adrenergic antagonists, epinephrine derivatives, miotics (pilocarpine and carbachol), strong miotics (echothiopate iodide), and systemic carbonic anhydrase inhibitors. The mean number of medications used before argon laser trabeculoplasty was 3.4 ± 1.0 (mean ± SO). Argon laser trabeculoplasty treatments were performed in a single session with approximately 100 laser applications (range, 80-11 0) equally distributed around the entire angle circumference. The argon laser (Coherent Radiation Model 900, Palo Alto, CA) application parameters were 50 ~m spot size, 700 to 1200 m W power, and 0.1 second duration. Treatment was directed at the mid-to-anterior pigmented trabecular meshwork with a desired reaction of blanching and minimal vacuolization. Patients maintained their pretreatment glaucoma medical regimen after laser therapy and used topical steroids (fluorometholone, dexamethasone alcohol, or prednisolone acetate) in the treated eye for 3 to 5 days. The mean follow-up was 37 ± 24 months (mean ± SO) (range, 1-68 months). Clinical criteria for success included no progressive optic nerve damage or glaucomatous visual field loss, no laser retreatment or glaucoma surgical intervention, and final lOP ofless than or equal to 19 mmHg and at least 3 mmHg below the pretreatment level. Eyes were considered failures and eliminated from further follow-up if they did not meet these criteria; thus, failed eyes contributed to lOP analysis only up to and including their date of failure. The 1514
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criteria were based on similar standards used by others6 •7 in order to permit meaningful comparison. Twelve patients considered successful had follow-up less than 48 months due to patient death (7 patients) or inability to maintain follow-up (5 patients) and were included in this study. Data evaluation incorporated life-table analysis methods to account for varying follow-up periods. Baseline documentation of optic nerve status was made for each patient before argon laser trabeculoplasty by detailed diagrams and stereoscopic photographs. Assessment of changes were made at each follow-up visit by direct ophthalmoscopy and contact lens funduscopy. Evidence of progressive change in optic nerve cupping from baseline placed a patient in the failure category. When visual acuity was adequate, baseline visual fields were established for each patient before argon laser trabeculoplasty with either a Goldmann perimeter, Octopus computerized perimeter (lnterzeag AG, Switzerland) or Humphrey field analyzer (Humphrey Instruments, San Leandro, CA). Visual fields were monitored, on the average, once per year during follow-up using consistent testing parameters. The Armaly-Drance method of kinetic perimetry9 was used for Goldmann visual fields. Static threshold perimetry was performed using programs 31, 32, or 34 on an Octopus computerized perimeter (Model 2000) and programs 30-1 and 30-2 on a Humphrey field analyzer. Documentation of significant visual field change required identification of a new scotoma or enlargement and increased density of existing scotomas reproducible on repeat testing. Visual field loss was not quantified. The goals of data analysis were to describe changes in lOP after treatment and differences in rate of success between subgroups. Differences between pretreatment and posttreatment lOP in any given individual were evaluated by paired t tests. Intraocular pressure changes were also evaluated statistically by computing the slope of the regression line of lOP versus time for each individual with at least two measurements after argon laser trabeculoplasty. Differences in mean slopes between successful and failing groups were compared by unpaired t tests. Nonparametric and parametric survival techniques were used to analyze success rates. The Kaplan-Meier approach 10 was used to obtain estimates of failure by specific time points. This survival analysis approach accounted for varying follow-up periods due to patient death or patients lost to follow-up. Comparison in failure rates between subgroups of lOP and between diagnostic groups used Breslow's version of the generalized Wilcoxon test. 11 Multivariate analysis of predictors of failure used Cox's proportional hazards model. 12 Parameters were estimated by maximizing the partial likelihood as implemented by the BMDP statistical package.U
RESULTS Table 1 summarizes the lOPs after argon laser trabeculoplasty. Mean lOPs at each of the follow-up dates
SHINGLETON et al
were significantly lower than the mean pretreatment lOPs (P < 0.0001). The decrease in lOP from the mean pretreatment level ranged from 7.6 ± 6.4 mmHg (mean ± SD) at 1 month to 10.7 ± 3.9 mmHg (mean± SD) at 60 months after treatment. Failed eyes and eyes lost to follow-up were withdrawn from further lOP evaluation after their elimination date but were included in lifetable analyses. The long-term results reflect only those eyes that remained successful; other eyes only contributed to the data up to and including their time of failure or dropout from the study. Seventy-two percent of eyes (67 /93) had a final lOP of at least 3 mmHg below the pretreatment level and 56% of eyes (52/93) had a final lOP of less than or equal to 19 mmHg. The mean decrease in final lOP for all 93 eyes was 6.3 ± 7.3 mmHg (mean± SD). In order to describe the long-term trends after argon laser trabeculoplasty, we calculated the slopes of lOP versus time for the 80 eyes with at least two lOP measurements after laser treatment. Thirteen eyes did not have two post-laser lOP measurements; 11 eyes were failures by 1 month and two patients died. Slopes ofiOP measurements provide further information on longterm follow-up because they do not selectively delete eyes with high lOPs. The mean slope ofiOPs for the 80 eyes increased only 0.01 ± 0.34 mmHg (mean± SD) per month after treatment. This demonstrates the relative stability of mean lOP reduction after argon laser trabeculoplasty (Fig 1). The mean slopes of posttreatment lOPs were different in successful and failed eyes. The lOPs for successful eyes decreased 0.10 ± 0.35 mmHg (mean ± SD) per month and the lOP for failed eyes increased 0.12 ± 0.29 mmHg (mean ± SD) per month (P < 0.003). The final lOP reduction for 41 successful eyes was 10.8 ± 5.5 mmHg (mean ± SD). The final lOP reduction for 52 failed eyes was 2.8 ± 5.8 mmHg (mean± SD). Although lOP reduction was less in the failure group than in the successful group, the mean decrease in final lOP for failed eyes represents a significant decrease from the pretreatment level (P < 0.01 ). The Kaplan-Meier survival curve for time to failure is presented in Figure 2. The probability of remaining successful up to 4 years was 52% for all 93 eyes. The highest probability for failure was in the first year with a cumulative failure rate of 23%. In subsequent years, the probability of failure was 7 to 10% per year. Life-table analysis of the 60 eyes with primary open-angle glaucoma (without prior surgical intervention, pseudoexfoliation, or low pretreatment lOP) disclosed a similar probability of remaining successful up to 4 years of 57%. Table 2 shows the probability of success at 2, 3, 4, and 5 years after argon laser trabeculoplasty, gi¥en success at 1 year. If an eye was successful at 1 year,,the probability of remaining successful up to 4 years after initial treatment was 68%. In addition, Table 2 presents the specific number of patients involved in life-table analysis for each half-year interval from 0 to 5 years after argon laser trabeculoplasty. Tliis table details the number offailures during each half-year interval and the number of pa-
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LONG-TERM ALT
'B)
40
.§.
30
~
e 26.1
Average pretreatment lOP
~
.t 18.520!!-.fo--------------10
0
~----~----~----~----~----~~
12
24
36
48
60
Month of Follow Up Fig 1. Change in lOP after argon laser trabeculoplasty.
1.0 Cl,)
~ 0.8
(,)
(,)
:::3
Cl) .... 0
0.6
;if!...:::: 0.4
:a .8 e Cl.
0.2 0
6
12 18 24 30 36 42 48 54 60
Time (months) Fig 2. Survival curve for time to failure after argon laser trabeculoplasty.
tients withdrawn due to death or inability to maintain follow-up. Life-table analyses were also performed for time-tolaser retreatment or glaucoma surgical intervention and time to an lOP greater than 19 mmHg. The life-table estimate of the probability of additional laser or surgical therapy by 4 years was 41%. The probability of maintaining an lOP ofless than or equal to 19 mmHg for up to 4 years was 35%. Of the 93 eyes included in this study, 52 failed during follow-up for one or more of the following reasons. Six eyes (7%) showed evidence of progressive optic nerve damage or glaucomatous visual field loss; 15 ( 16%) required laser retreatment and 37 (40%) underwent filtration surgery because of progressive visual field loss or unacceptably high lOPs. Forty-one eyes (44%) failed to have a final lOP of at least 3 mmHg below the pretreatment level or a final lOP of less than or equal to 19 mmHg. If the requirement of an lOP of less than or equal to 19 mmHg throughout the course of follow-up is added to the criteria for success, 71 eyes (76%) failed. Survival analysis demonstrated no significant differences in failure rates between groups with pretreatment 1515
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Table 2. Life-table Analysis of Time to Failure after Argon Laser Trabeculoplasty Time after Treatment (yrs)
No. of Eyes
No. of Failures
No. of Eyes Withdrawn
Cumulative Probability of Success
0-0.5 0.5-1.0 1.0-1.5 1.5-2.0 2.0-2.5 2.5-3.0 3.0-3.5 3.5-4.0 4.0-4.5 4.5-5.0
93 76 66 63 58 53 49 47 36 31
13 8 3 3 4 2 1 7 2 3
4 2 0 2 1 2 1 4* 3 13
0.86 0.77 0.73 0.70 0.65 0.62 0.61 0.52 0.49 0.44
* These
0.91 0.81 0.68 0.57
Standard Error
0.037 0.044 0.047 0.049 0.051 0.052 0.052 0.055 0.055 0.057
4 eyes had 48 months of follow-up, but no follow-up thereafter.
lOPs less than 22 mmHg, 23 to 29 mmHg, or greater than 30 mmHg. A similar analysis based on diagnosis did not show significant differences in success rates between eyes with primary open-angle glaucoma, pseudoexfoliation glaucoma, or those with pre-laser lOPs less than or equal to 19 mmHg. The median time to failure was shortest for eyes with pretreatment pressures less than or equal to 19 mmHg (24 months) compared with 42 months for pseudoexfoliation glaucoma and 54 months for primary open-angle glaucoma, but the number of eyes was too small for these differences to achieve statistical significance. The Cox proportional hazards model also showed no significant effect of pretreatment lOP, age, sex, or diagnosis on success of treatment. With regard to the effect of previous intraocular surgery, the 16 eyes that had undergone glaucoma or cataract surgery before argon laser trabeculoplasty were compared with eyes not having had any type of previous ocular surgery. Both groups had primary open-angle glaucoma and no significant differences in success were found. In addition, ten eyes underwent cataract extraction at varying times after laser trabeculoplasty (24 ± 20 months [mean± SD]; range, 3-60 months). All eyes, except one, remained successful for the duration of follow-up (32 ± 23 months [mean ± SD); range, 3-54 months). Medications were reduced only slightly in the successful group. The mean reduction in number of medications for successful eyes was 0.5 ± 0.8 (mean + SO) compared with a reduction of 0.1 ± 0.7 (mean± SO) for failing eyes (P < 0.04 ). One eye appeared to be made worse by argon laser trabeculoplasty, as the lOP increased more than 10 mmHg above the pretreatment level within I month of the initial treatment and required filtration surgery. No emergency surgery was required as a result of argon laser trabeculoplasty. Five eyes required laser retreatment or filtration surgery based on optic nerve changes or progressive visual field loss despite final lOP reduction of more than 3 mmHg and consistent tonometry readings of less than or equal to 19 mmHg. 1516
Probability of Success Given Survival at 1 yr
DISCUSSION Following Wise and Witter's 1 initial report of a substantial reduction in lOP after argon laser trabeculoplasty, early success with lOP control and avoidance of glaucoma surgery has been confirmed by others. 2 •3 Wise4 extended his follow-up to 6 months or more for 150 eyes. Six percent of the eyes required glaucoma surgery during follow-up and the average lOP reduction did not diminish with time. As only 11 eyes were seen 4 years after treatment, this study was limited in establishing the frequency of a long-lasting reduction in lOP after argon laser trabeculoplasty. Pohjanpelto 5 followed pseudoexfoliation and primary open-angle glaucoma patients for 18 to 42 months. Ninety-five percent of eyes with pseudoexfoliation were initially controlled, but 10% were termed late failures (control is defined as lOP < 22 mmHg and a pressure reduction of 20% from the pretreatment level). Seventysix percent of eyes with primary open-angle glaucoma were initially controlled, but one eye was a late failure. Schwartz and Kopelman 6 reported successful control (stable visual field and optic nerve as well as a decrease in lOP> 4 mmHg compared with baseline) in 77% of a predominately black population with a mean follow-up of 24 months. They documented a gradual increase in lOP for all eyes with time. Extended follow-up of the same population, with 13 successful eyes being followed for 5 years, demonstrated a decrease in success rate to 46%. Results were more successful in white patients (65%) than black patients (32%). 7 Our study establishes that argon laser trabeculoplasty is effective in reducing lOP in most patients followed up to 5 years. The mean final decrease in lOP for all 93 eyes was greater than 6 mmHg. The mean lOP reduction for all eyes changed only slightly over time. Seventy-two percent of eyes had a final lOP of at least 3 mmHg below the pretreatment level and 56% of eyes had a final lOP of less than or equal to 19 mmHg. Despite a significant mean decrease in lOP for our
SHINGLETON et al
entire study group, the determination of success after argon laser trabeculoplasty was not made purely on the basis of lOP. The determination of a safe lOP level and the need for further laser or surgical treatment were affected by multiple variables, including clinical judgments on optic nerve and visual field status. Consequently, success rates varied depending on which of these criteria were used for defining satisfactory control. At a minimum, a sufficient reduction in lOP to protect the optic nerve, to protect the field of vision, and to avoid further laser or surgical intervention were criteria that had to be met for success. Using these criteria, we found the probability of remaining successful up to 4 years after argon laser trabeculoplasty to be 52%. This suggests that approximately one half of the patients who might have otherwise undergone filtration surgery in the past may avoid such intervention for an extended period of time after argon laser trabeculoplasty. Since failure occurred more frequently in the first year after argon laser trabeculoplasty, it should be noted that if a patient is successful at 1 year, the probability of that patient remaining successful up to 4 years after argon laser trabeculoplasty increased to 68%. Although the lOP may be lowered sufficiently after argon laser trabeculoplasty to avoid surgery, vigilance is required in order to detect progressive visual field loss during follow-up. As some eyes with profound optic nerve damage require low normal pressures, a final lOP much lower than 19 mmHg and an lOP reduction much greater than 3 mmHg may be needed. This point is supported by the fact that progressive glaucomatous optic nerve damage developed in five patients and they needed further laser or surgical treatment despite significant posttreatment pressure reduction and consistent tonometry measurements less than or equal to 19 mmHg. These eyes are similar to Pohjanpelto's finding 5 of visual field deterioration in some eyes despite pressure reduction to 22 mmHg or less after laser treatment and the finding of Schwartz et aC of progressive field loss in some eyes despite lOPs in the mid teens. These observations emphasize that close observation is required of apparently successful eyes in order to avoid progressive nerve damage and visual field loss. Controversies exist as to the effect of various modifying factors on argon laser trabeculoplasty results. In particular the effects of baseline lOP 7•14 diagnosis 2 •5- 7 •14 age 2 •3 ~nd previous surgery 15 on lOP reduction by' argon laser trabeculoplasty have been studied. Others have found a positive correlation between the amount ofiOP reduction and the pretreatment level, 14 but our study failed to demonstrate significant differences in success rates between groups with 'pretreatment lOPs of less than 22, 23 to 29, or greater than 30 mmHg. In terms of diagnosis, pseudoexfoliation has been' variably associated with success after treatment. 2 •3•5•7•14 No significant difference in success rates between pseudoexfoliation and primary open-angle glaucoma patients was established in our study. Age or previous intraocular surgery status did not significantly affect success rates after treatment in our population.
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Argon laser trabeculoplasty infrequently eliminates the need for medications after treatment. Pollack et al 16 also found that most patients are dependent on medications after laser treatment. This demonstrates the need for continued patientcompliance with glaucoma medical treatment after argon laser trabeculoplasty and for physician monitoring. Careful management is required in the early weeks after argon laser trabeculoplasty as demonstrated by the single patient who had persistent pressure elevation after treatment. Intraocular pressure elevation after 360° or 180° argon laser trabeculoplasty has been shown to be an infrequent but important complication. 2 •3 It is important to measure the lOP approximately 1 hour after laser trabeculoplasty and modify treatment and followup thereafter depending on the level of lOP and optic nerve status. This study demonstrates that argon laser trabeculoplasty is an effective means of reducing lOP in many eyes with open-angle glaucoma. The average lOP lowering effect remains fairly stable with extended observation; however, up to 50% of eyes with advanced glaucoma may require laser retreatment or glaucoma surgery within 5 years of the initial treatment session.
REFERENCES 1. Wise JB, Witter SL. Argon laser therapy for open angle glaucoma: a pilot study. Arch Ophthalmol1979; 97:319-22. 2. Thomas JV, Simmons RJ, Belcher CD Ill. Argon laser trabeculoplasty in the presurgical glaucoma patient. Ophthalmology 1982; 89:18797. 3. Schwartz AL, Whitten ME, Bleiman B, Martin D. Argon laser trabecular surgery in uncontrolled phakic open angle glaucoma. Ophthalmology 1981; 88:203-12 4. Wise JB. Long-term control of adult open angle glaucoma by argon laser treatment. Ophthalmology 1981; 88:197-202. 5. Pohjanpelto P. Late results of laser trabeculoplasty for increased intraocular pressure. Acta Ophthalmol 1983; 61:998-1008. 6. Schwartz AL, Kopelman J. Four-year experience with argon laser trabecular surgery in uncontrolled open-angle glaucoma. Ophthalmology 1983; 90:771-80. 7. Schwartz AL, Love DC, Schwartz MA. Long-term follow-up of argon laser trabeculoplasty for uncontrolled open-angle glaucoma. Arch Ophthalmol1985; 103:1482-4. 8. Rosner B. Multivariate methods in ophthalmology with application to other paired-data situations. Biometrics 1984; 40:1025-35. 9. Rock WJ, Drance SM, Morgan RW. Visual field screening in glaucoma: an evaluation of the Armaly technique for screening glaucomatous visual fields. Arch Ophthalmol 1973; 89:287-90. 10. Kaplan EL, Meier P. Nonparametric estimation from incomplete observations. J Am Stat Assoc 1958; 53:457-81. 11. Breslow N. A generalized Kruskai-Wallis test for comparing K samples subject to unequal patterns of censorship. Biometrika 1970; 57:579-94. 12. Cox DR. Regression models and life tables. J Royal Stat Soc Series B, 1972; 34:187-220. 13. Dixon WJ, ed. BMDP Statistical Software. University of California Press, 1985. 14. Traverso CE, Spaeth GL, Starita RJ, et al. Factors affecting the results of argon laser trabeculoplasty in open-angle glaucoma. Ophthalmic Surg 1986; 17:554-9.
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15. Brown SVL, Thomas JV, Budenz DL, et al. Effect of cataract surgery on intraocular pressure reduction obtained with laser trabeculoplasty. Am J Ophthalmol1985; 100:373-6.
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16. Pollack IP, Robin AL, Sax H. The effect of argon laser trabeculoplasty on the medical control of primary open-angle glaucoma. Ophthalmology 1983; 90:785-9.
Discussion
by
Douglas R. Anderson, MD Shingleton and co-workers have brought us up-to-date on long-term results of argon laser trabeculoplasty. To judge whether the outcome is good or bad, we of course compare the results with what we think would have happened with some alternate management (i.e., continued full medical therapy with suboptimal pressure, or trabeculectomy with its attendant better pressure control but also additional expense and risk of complication). Ideally, we might hope for some randomized prospective trial comparing argon laset trabeculoplasty with one or another alternate, but such data are lacking, and we must see what we can conclude about argon laser trabeculoplasty with the available information. First, argon laser trabeculoplasty does lower intraocular pressure (lOP) in the majority of patients treated. Some enjoy pressure lowering without the need for continued medication, but many must continue at least some of their medications. Separate from these prompt "successes" are 20 to 25% who, practically from the start, had inadequate lowering ofiOP and therefore undergo a second laser treatment or surgery within 1 year (a second laser treatment usually did not work, and all but 4 of 15 such patients subsequently required filtration surgery)_ From among the 75 to 80% who did not suffer prompt failure, most maintained a controlled pressure with stable discs and fields for the duration of follow-up. However, some later failed in one of three ways. A very few had partial lowering of pressure, and the surgeon deferred judgment for more than I year before finally deciding that the pressure was still worrisome and that it was prudent to perform surgery. More often, the pressure increased after initial adequate lowering of pressure, and for that reason further intervention was required. A third type of late failure was represented by five cases of progressive change in disc or field (or both), four of which did so despite normal lOP. In total, through one of these three courses, the late failures occurred at a rate of 10% (of the remaining successes) per year. Thus, a 75% success at 1 year is reduced to 50% success by the end of 5 years.
From the Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami. Supported in part by the National Glaucoma Research, a program of American Health Assistance Foundation, Rockville, Maryland. Reprint requests to Douglas R. Anderson, MD, Bascom Palmer Eye Institute, PO Box 016880, Miami, FL 33101.
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One might hope for better results, but after 5 years at least half of the patients had avoided surgery. That benefit is seemingly enough to confirm our belief that argon laser trabeculoplasty should be done first whenever medical therapy has failed and surgery is the only other alternative-unless you believe that the group would have been better off if all had filtration surgery. This would be true, for example, if delay in the unsuccessful laser cases caused further visual loss to occur before the filtration surgery was done. Evidently, this does not occur. Five cases did have further nerve damage or field loss, but in only one case did this occur because of inadequate pressure lowering. (One must trust that indications for argon laser trabeculoplasty were such that field loss would have occurred without intervention in substantially more than 5 cases). Thus, the following two conclusions may be reached. (I) The occurrence of nerve damage and field loss is reduced by the use of argon laser trabeculoplasty in cases with apparently inadequate response to medical therapy. One might like a randomized clinical trial in which half of such patients are followed as a comparison group without intervention in order to establish that the intervention definitely results in a lower incidence of field loss. However, one would have to be far off in clinical judgment of when argon laser trabeculoplasty is indicated for the nonintervention group to have only a 5% incidence of field loss. (2) Primary use of argon laser trabeculoplasty followed by trabeculectomy in selected cases is a better strategy than prompt filtration surgery for all cases. Filtration surgery does seem more often to achieve lower lOP without the need for continued medication, but again, one might hope for a randomized trial comparing these two alternatives in order to be sure. However, our collective clinical judgment currently might be that cataract formation, longer postoperative recovery, and occasional disasterous results might too high a price to pay: the current strategy reduces field loss to 5% and elimination of that 5% risk is the most benefit that the surgery-in-all-cases strategy could achieve. Moreover, we know that surgery too has a certain rate oflate failure to control the lOP. Therefore, the current data suggest that the strategy of using laser before surgery is on track.
Abstract: Long-term efficacy of 360° argon laser trabeculoplasty was studied in 118 eyes of 93 patients with uncontrolled chronic open-angle glaucoma. The mean intraocular pressure (lOP) decrease was 8.9 ± 5.4 mmHg (mean ± standard deviation [SO] in 71 eyes at 1 year, 9.3 ± 4.3 mmHg (mean ± SD) in 51 eyes at 3 years, and 10.3 ± 3.9 mmHg (mean ± SD) in 28 eyes at 5 years. The probability of success at 4 years (decrease in lOP~ 3 mmHg, lOP :s; 19 mmHg, stable visual field, stable optic nerve, and no further laser or surgical intervention) was 52%. Pretreatment lOP, diagnosis, previous operations, age, and sex were not significant determinants for success or failure. Eyes receiving argon laser trabeculoplasty before cataract surgery maintained control of lOP after surgery. Failure was most common in the first year after treatment (23%), and thereafter failure occurred at a rate of 7 to 10% per year. [Key words: argon laser trabeculoplasty, cataract surgery, filtration surgery, intraocular pressure, Kaplan-Meier survival analysis, optic nerve, primary open-angle glaucoma, proportional hazards model, pseudoexfoliation, visual field.] Ophthalmol qy 94:1513-1518, 1987
Argon laser trabeculoplasty has become an integral part of the ophthalmologist's program for the treatment of open-angle glaucoma. It is a relatively safe outpatient procedure, well tolerated by patients, and has been reported1-3 to lower intraocular pressure (lOP) sufficiently to postpone or prevent glaucoma surgery in 82 to 97% of patients followed from 6 to 24 months. However, concern remains about its long-term effectiveness. Reports with follow-up extending from 1 to 5 years 4 - 7 claim varying success rates from 46 to 94%. This study was designed to further evaluate the long-term efficacy of argon laser trabeculoplasty in controlling lOP, preventing glaucomatous visual loss, and avoiding further laser or surgical intervention in open-angle glaucoma patients.
of
From the Glaucoma SeNice,* Ophthalmic Consultants Boston, Inc, the Glaucoma Consultation SeNice and Epidemiology Unit,t Massachusetts Eye and Ear Infirmary, and the Department of Ophthalmology, HaNard Medical School, Boston. Presented at the American Academy of Ophthalmology Annual Meeting, New Orleans, November 1986.' Reprint requests to Bradford J. Shingleton, MD, Ophthalmic Consultants of Boston, Inc, 50 Staniford Street, Boston, MA 02114.
MATERIALS AND METHODS This retrospective study reviewed 118 eyes of93 consecutive patients with chronic open-angle glaucoma and pseudoexfoliation glaucoma treated by argon laser trabeculoplasty between October 1979 and June 1981. The results in the two eyes in 23 of25 patients treated bilaterally were identical and indicated a high degree of association between the response in fellow eyes. As an analysis which considers pairs of eyes from the same individual as independent observations may be inappropriate, 8 only one of a pair of eyes, randomly selected, was analyzed. The mean age of the 93 patients included in the study was 69.5 ± 8.2 years (mean± standard deviation [SD]) (range, 50-93 years). Fifty-eight percent of the patients were women, 95% were white. Seventy-six eyes had primary open-angle glaucoma, 11 had pseudoexfoliation glaucoma, and 6 had pre-laser lOPs ofless than or equal to 19 mmHg. Patients with other types of secondary open-angle glaucoma, angle-closure glaucoma, and congenital glaucoma were excluded. Sixteen of the eyes with primary open-angle glaucoma had undergone previous surgery (5 eyes had cataract surgery, 4 had filtration 1513
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Table 1. Mean lOPs after Argon Laser Trabeculoplasty Mo of Follow-up Pre-argon laser trabeculoplasty, baseline
1 6 12 18 24 30 36 42 48 54 60
lOP
=
lOP (mmHg) (mean± SO)
No. of Eyes
26.1 ± 18.5 ± 17.0 ± 17.0 ± 18.4 ± 16.8 ± 18.1 ± 16.4 ± 18.5 ± 16.8 ± 16.7 ± 15.4 ±
93 92 75 71 43 61 40 51 34 45 32 28
intraocular pressure; SO
=
5.5 6.2 5.0 4.8 4.4 3.5 3.8 3.6 4.7 4.4 4.8 3.4
Change in lOP (mean± SO)
-7.7 ± 6.4 -8.9 ± 5.4 -8.7 ± 4.6 -9.3 ± 4.3 -8.8 ± 5.5 -10.3 ± 3.9
standard deviation.
had combined cataract and filtration surgery, and 2 had peripheral iridectomies). All patients had either advanced glaucomatous optic nerve damage or significant lOP elevation and would have been candidates for filtration surgery before the introduction of argon laser trabeculoplasty. All patients were maintained on a maximally tolerated medical program for glaucoma control. Glaucoma medications used before argon laser trabeculoplasty included one or more of the following types: topical beta-adrenergic antagonists, epinephrine derivatives, miotics (pilocarpine and carbachol), strong miotics (echothiopate iodide), and systemic carbonic anhydrase inhibitors. The mean number of medications used before argon laser trabeculoplasty was 3.4 ± 1.0 (mean ± SO). Argon laser trabeculoplasty treatments were performed in a single session with approximately 100 laser applications (range, 80-11 0) equally distributed around the entire angle circumference. The argon laser (Coherent Radiation Model 900, Palo Alto, CA) application parameters were 50 ~m spot size, 700 to 1200 m W power, and 0.1 second duration. Treatment was directed at the mid-to-anterior pigmented trabecular meshwork with a desired reaction of blanching and minimal vacuolization. Patients maintained their pretreatment glaucoma medical regimen after laser therapy and used topical steroids (fluorometholone, dexamethasone alcohol, or prednisolone acetate) in the treated eye for 3 to 5 days. The mean follow-up was 37 ± 24 months (mean ± SO) (range, 1-68 months). Clinical criteria for success included no progressive optic nerve damage or glaucomatous visual field loss, no laser retreatment or glaucoma surgical intervention, and final lOP ofless than or equal to 19 mmHg and at least 3 mmHg below the pretreatment level. Eyes were considered failures and eliminated from further follow-up if they did not meet these criteria; thus, failed eyes contributed to lOP analysis only up to and including their date of failure. The 1514
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criteria were based on similar standards used by others6 •7 in order to permit meaningful comparison. Twelve patients considered successful had follow-up less than 48 months due to patient death (7 patients) or inability to maintain follow-up (5 patients) and were included in this study. Data evaluation incorporated life-table analysis methods to account for varying follow-up periods. Baseline documentation of optic nerve status was made for each patient before argon laser trabeculoplasty by detailed diagrams and stereoscopic photographs. Assessment of changes were made at each follow-up visit by direct ophthalmoscopy and contact lens funduscopy. Evidence of progressive change in optic nerve cupping from baseline placed a patient in the failure category. When visual acuity was adequate, baseline visual fields were established for each patient before argon laser trabeculoplasty with either a Goldmann perimeter, Octopus computerized perimeter (lnterzeag AG, Switzerland) or Humphrey field analyzer (Humphrey Instruments, San Leandro, CA). Visual fields were monitored, on the average, once per year during follow-up using consistent testing parameters. The Armaly-Drance method of kinetic perimetry9 was used for Goldmann visual fields. Static threshold perimetry was performed using programs 31, 32, or 34 on an Octopus computerized perimeter (Model 2000) and programs 30-1 and 30-2 on a Humphrey field analyzer. Documentation of significant visual field change required identification of a new scotoma or enlargement and increased density of existing scotomas reproducible on repeat testing. Visual field loss was not quantified. The goals of data analysis were to describe changes in lOP after treatment and differences in rate of success between subgroups. Differences between pretreatment and posttreatment lOP in any given individual were evaluated by paired t tests. Intraocular pressure changes were also evaluated statistically by computing the slope of the regression line of lOP versus time for each individual with at least two measurements after argon laser trabeculoplasty. Differences in mean slopes between successful and failing groups were compared by unpaired t tests. Nonparametric and parametric survival techniques were used to analyze success rates. The Kaplan-Meier approach 10 was used to obtain estimates of failure by specific time points. This survival analysis approach accounted for varying follow-up periods due to patient death or patients lost to follow-up. Comparison in failure rates between subgroups of lOP and between diagnostic groups used Breslow's version of the generalized Wilcoxon test. 11 Multivariate analysis of predictors of failure used Cox's proportional hazards model. 12 Parameters were estimated by maximizing the partial likelihood as implemented by the BMDP statistical package.U
RESULTS Table 1 summarizes the lOPs after argon laser trabeculoplasty. Mean lOPs at each of the follow-up dates
SHINGLETON et al
were significantly lower than the mean pretreatment lOPs (P < 0.0001). The decrease in lOP from the mean pretreatment level ranged from 7.6 ± 6.4 mmHg (mean ± SD) at 1 month to 10.7 ± 3.9 mmHg (mean± SD) at 60 months after treatment. Failed eyes and eyes lost to follow-up were withdrawn from further lOP evaluation after their elimination date but were included in lifetable analyses. The long-term results reflect only those eyes that remained successful; other eyes only contributed to the data up to and including their time of failure or dropout from the study. Seventy-two percent of eyes (67 /93) had a final lOP of at least 3 mmHg below the pretreatment level and 56% of eyes (52/93) had a final lOP of less than or equal to 19 mmHg. The mean decrease in final lOP for all 93 eyes was 6.3 ± 7.3 mmHg (mean± SD). In order to describe the long-term trends after argon laser trabeculoplasty, we calculated the slopes of lOP versus time for the 80 eyes with at least two lOP measurements after laser treatment. Thirteen eyes did not have two post-laser lOP measurements; 11 eyes were failures by 1 month and two patients died. Slopes ofiOP measurements provide further information on longterm follow-up because they do not selectively delete eyes with high lOPs. The mean slope ofiOPs for the 80 eyes increased only 0.01 ± 0.34 mmHg (mean± SD) per month after treatment. This demonstrates the relative stability of mean lOP reduction after argon laser trabeculoplasty (Fig 1). The mean slopes of posttreatment lOPs were different in successful and failed eyes. The lOPs for successful eyes decreased 0.10 ± 0.35 mmHg (mean ± SD) per month and the lOP for failed eyes increased 0.12 ± 0.29 mmHg (mean ± SD) per month (P < 0.003). The final lOP reduction for 41 successful eyes was 10.8 ± 5.5 mmHg (mean ± SD). The final lOP reduction for 52 failed eyes was 2.8 ± 5.8 mmHg (mean± SD). Although lOP reduction was less in the failure group than in the successful group, the mean decrease in final lOP for failed eyes represents a significant decrease from the pretreatment level (P < 0.01 ). The Kaplan-Meier survival curve for time to failure is presented in Figure 2. The probability of remaining successful up to 4 years was 52% for all 93 eyes. The highest probability for failure was in the first year with a cumulative failure rate of 23%. In subsequent years, the probability of failure was 7 to 10% per year. Life-table analysis of the 60 eyes with primary open-angle glaucoma (without prior surgical intervention, pseudoexfoliation, or low pretreatment lOP) disclosed a similar probability of remaining successful up to 4 years of 57%. Table 2 shows the probability of success at 2, 3, 4, and 5 years after argon laser trabeculoplasty, gi¥en success at 1 year. If an eye was successful at 1 year,,the probability of remaining successful up to 4 years after initial treatment was 68%. In addition, Table 2 presents the specific number of patients involved in life-table analysis for each half-year interval from 0 to 5 years after argon laser trabeculoplasty. Tliis table details the number offailures during each half-year interval and the number of pa-
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LONG-TERM ALT
'B)
40
.§.
30
~
e 26.1
Average pretreatment lOP
~
.t 18.520!!-.fo--------------10
0
~----~----~----~----~----~~
12
24
36
48
60
Month of Follow Up Fig 1. Change in lOP after argon laser trabeculoplasty.
1.0 Cl,)
~ 0.8
(,)
(,)
:::3
Cl) .... 0
0.6
;if!...:::: 0.4
:a .8 e Cl.
0.2 0
6
12 18 24 30 36 42 48 54 60
Time (months) Fig 2. Survival curve for time to failure after argon laser trabeculoplasty.
tients withdrawn due to death or inability to maintain follow-up. Life-table analyses were also performed for time-tolaser retreatment or glaucoma surgical intervention and time to an lOP greater than 19 mmHg. The life-table estimate of the probability of additional laser or surgical therapy by 4 years was 41%. The probability of maintaining an lOP ofless than or equal to 19 mmHg for up to 4 years was 35%. Of the 93 eyes included in this study, 52 failed during follow-up for one or more of the following reasons. Six eyes (7%) showed evidence of progressive optic nerve damage or glaucomatous visual field loss; 15 ( 16%) required laser retreatment and 37 (40%) underwent filtration surgery because of progressive visual field loss or unacceptably high lOPs. Forty-one eyes (44%) failed to have a final lOP of at least 3 mmHg below the pretreatment level or a final lOP of less than or equal to 19 mmHg. If the requirement of an lOP of less than or equal to 19 mmHg throughout the course of follow-up is added to the criteria for success, 71 eyes (76%) failed. Survival analysis demonstrated no significant differences in failure rates between groups with pretreatment 1515
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Table 2. Life-table Analysis of Time to Failure after Argon Laser Trabeculoplasty Time after Treatment (yrs)
No. of Eyes
No. of Failures
No. of Eyes Withdrawn
Cumulative Probability of Success
0-0.5 0.5-1.0 1.0-1.5 1.5-2.0 2.0-2.5 2.5-3.0 3.0-3.5 3.5-4.0 4.0-4.5 4.5-5.0
93 76 66 63 58 53 49 47 36 31
13 8 3 3 4 2 1 7 2 3
4 2 0 2 1 2 1 4* 3 13
0.86 0.77 0.73 0.70 0.65 0.62 0.61 0.52 0.49 0.44
* These
0.91 0.81 0.68 0.57
Standard Error
0.037 0.044 0.047 0.049 0.051 0.052 0.052 0.055 0.055 0.057
4 eyes had 48 months of follow-up, but no follow-up thereafter.
lOPs less than 22 mmHg, 23 to 29 mmHg, or greater than 30 mmHg. A similar analysis based on diagnosis did not show significant differences in success rates between eyes with primary open-angle glaucoma, pseudoexfoliation glaucoma, or those with pre-laser lOPs less than or equal to 19 mmHg. The median time to failure was shortest for eyes with pretreatment pressures less than or equal to 19 mmHg (24 months) compared with 42 months for pseudoexfoliation glaucoma and 54 months for primary open-angle glaucoma, but the number of eyes was too small for these differences to achieve statistical significance. The Cox proportional hazards model also showed no significant effect of pretreatment lOP, age, sex, or diagnosis on success of treatment. With regard to the effect of previous intraocular surgery, the 16 eyes that had undergone glaucoma or cataract surgery before argon laser trabeculoplasty were compared with eyes not having had any type of previous ocular surgery. Both groups had primary open-angle glaucoma and no significant differences in success were found. In addition, ten eyes underwent cataract extraction at varying times after laser trabeculoplasty (24 ± 20 months [mean± SD]; range, 3-60 months). All eyes, except one, remained successful for the duration of follow-up (32 ± 23 months [mean ± SD); range, 3-54 months). Medications were reduced only slightly in the successful group. The mean reduction in number of medications for successful eyes was 0.5 ± 0.8 (mean + SO) compared with a reduction of 0.1 ± 0.7 (mean± SO) for failing eyes (P < 0.04 ). One eye appeared to be made worse by argon laser trabeculoplasty, as the lOP increased more than 10 mmHg above the pretreatment level within I month of the initial treatment and required filtration surgery. No emergency surgery was required as a result of argon laser trabeculoplasty. Five eyes required laser retreatment or filtration surgery based on optic nerve changes or progressive visual field loss despite final lOP reduction of more than 3 mmHg and consistent tonometry readings of less than or equal to 19 mmHg. 1516
Probability of Success Given Survival at 1 yr
DISCUSSION Following Wise and Witter's 1 initial report of a substantial reduction in lOP after argon laser trabeculoplasty, early success with lOP control and avoidance of glaucoma surgery has been confirmed by others. 2 •3 Wise4 extended his follow-up to 6 months or more for 150 eyes. Six percent of the eyes required glaucoma surgery during follow-up and the average lOP reduction did not diminish with time. As only 11 eyes were seen 4 years after treatment, this study was limited in establishing the frequency of a long-lasting reduction in lOP after argon laser trabeculoplasty. Pohjanpelto 5 followed pseudoexfoliation and primary open-angle glaucoma patients for 18 to 42 months. Ninety-five percent of eyes with pseudoexfoliation were initially controlled, but 10% were termed late failures (control is defined as lOP < 22 mmHg and a pressure reduction of 20% from the pretreatment level). Seventysix percent of eyes with primary open-angle glaucoma were initially controlled, but one eye was a late failure. Schwartz and Kopelman 6 reported successful control (stable visual field and optic nerve as well as a decrease in lOP> 4 mmHg compared with baseline) in 77% of a predominately black population with a mean follow-up of 24 months. They documented a gradual increase in lOP for all eyes with time. Extended follow-up of the same population, with 13 successful eyes being followed for 5 years, demonstrated a decrease in success rate to 46%. Results were more successful in white patients (65%) than black patients (32%). 7 Our study establishes that argon laser trabeculoplasty is effective in reducing lOP in most patients followed up to 5 years. The mean final decrease in lOP for all 93 eyes was greater than 6 mmHg. The mean lOP reduction for all eyes changed only slightly over time. Seventy-two percent of eyes had a final lOP of at least 3 mmHg below the pretreatment level and 56% of eyes had a final lOP of less than or equal to 19 mmHg. Despite a significant mean decrease in lOP for our
SHINGLETON et al
entire study group, the determination of success after argon laser trabeculoplasty was not made purely on the basis of lOP. The determination of a safe lOP level and the need for further laser or surgical treatment were affected by multiple variables, including clinical judgments on optic nerve and visual field status. Consequently, success rates varied depending on which of these criteria were used for defining satisfactory control. At a minimum, a sufficient reduction in lOP to protect the optic nerve, to protect the field of vision, and to avoid further laser or surgical intervention were criteria that had to be met for success. Using these criteria, we found the probability of remaining successful up to 4 years after argon laser trabeculoplasty to be 52%. This suggests that approximately one half of the patients who might have otherwise undergone filtration surgery in the past may avoid such intervention for an extended period of time after argon laser trabeculoplasty. Since failure occurred more frequently in the first year after argon laser trabeculoplasty, it should be noted that if a patient is successful at 1 year, the probability of that patient remaining successful up to 4 years after argon laser trabeculoplasty increased to 68%. Although the lOP may be lowered sufficiently after argon laser trabeculoplasty to avoid surgery, vigilance is required in order to detect progressive visual field loss during follow-up. As some eyes with profound optic nerve damage require low normal pressures, a final lOP much lower than 19 mmHg and an lOP reduction much greater than 3 mmHg may be needed. This point is supported by the fact that progressive glaucomatous optic nerve damage developed in five patients and they needed further laser or surgical treatment despite significant posttreatment pressure reduction and consistent tonometry measurements less than or equal to 19 mmHg. These eyes are similar to Pohjanpelto's finding 5 of visual field deterioration in some eyes despite pressure reduction to 22 mmHg or less after laser treatment and the finding of Schwartz et aC of progressive field loss in some eyes despite lOPs in the mid teens. These observations emphasize that close observation is required of apparently successful eyes in order to avoid progressive nerve damage and visual field loss. Controversies exist as to the effect of various modifying factors on argon laser trabeculoplasty results. In particular the effects of baseline lOP 7•14 diagnosis 2 •5- 7 •14 age 2 •3 ~nd previous surgery 15 on lOP reduction by' argon laser trabeculoplasty have been studied. Others have found a positive correlation between the amount ofiOP reduction and the pretreatment level, 14 but our study failed to demonstrate significant differences in success rates between groups with 'pretreatment lOPs of less than 22, 23 to 29, or greater than 30 mmHg. In terms of diagnosis, pseudoexfoliation has been' variably associated with success after treatment. 2 •3•5•7•14 No significant difference in success rates between pseudoexfoliation and primary open-angle glaucoma patients was established in our study. Age or previous intraocular surgery status did not significantly affect success rates after treatment in our population.
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LONG-TERM ALT
Argon laser trabeculoplasty infrequently eliminates the need for medications after treatment. Pollack et al 16 also found that most patients are dependent on medications after laser treatment. This demonstrates the need for continued patientcompliance with glaucoma medical treatment after argon laser trabeculoplasty and for physician monitoring. Careful management is required in the early weeks after argon laser trabeculoplasty as demonstrated by the single patient who had persistent pressure elevation after treatment. Intraocular pressure elevation after 360° or 180° argon laser trabeculoplasty has been shown to be an infrequent but important complication. 2 •3 It is important to measure the lOP approximately 1 hour after laser trabeculoplasty and modify treatment and followup thereafter depending on the level of lOP and optic nerve status. This study demonstrates that argon laser trabeculoplasty is an effective means of reducing lOP in many eyes with open-angle glaucoma. The average lOP lowering effect remains fairly stable with extended observation; however, up to 50% of eyes with advanced glaucoma may require laser retreatment or glaucoma surgery within 5 years of the initial treatment session.
REFERENCES 1. Wise JB, Witter SL. Argon laser therapy for open angle glaucoma: a pilot study. Arch Ophthalmol1979; 97:319-22. 2. Thomas JV, Simmons RJ, Belcher CD Ill. Argon laser trabeculoplasty in the presurgical glaucoma patient. Ophthalmology 1982; 89:18797. 3. Schwartz AL, Whitten ME, Bleiman B, Martin D. Argon laser trabecular surgery in uncontrolled phakic open angle glaucoma. Ophthalmology 1981; 88:203-12 4. Wise JB. Long-term control of adult open angle glaucoma by argon laser treatment. Ophthalmology 1981; 88:197-202. 5. Pohjanpelto P. Late results of laser trabeculoplasty for increased intraocular pressure. Acta Ophthalmol 1983; 61:998-1008. 6. Schwartz AL, Kopelman J. Four-year experience with argon laser trabecular surgery in uncontrolled open-angle glaucoma. Ophthalmology 1983; 90:771-80. 7. Schwartz AL, Love DC, Schwartz MA. Long-term follow-up of argon laser trabeculoplasty for uncontrolled open-angle glaucoma. Arch Ophthalmol1985; 103:1482-4. 8. Rosner B. Multivariate methods in ophthalmology with application to other paired-data situations. Biometrics 1984; 40:1025-35. 9. Rock WJ, Drance SM, Morgan RW. Visual field screening in glaucoma: an evaluation of the Armaly technique for screening glaucomatous visual fields. Arch Ophthalmol 1973; 89:287-90. 10. Kaplan EL, Meier P. Nonparametric estimation from incomplete observations. J Am Stat Assoc 1958; 53:457-81. 11. Breslow N. A generalized Kruskai-Wallis test for comparing K samples subject to unequal patterns of censorship. Biometrika 1970; 57:579-94. 12. Cox DR. Regression models and life tables. J Royal Stat Soc Series B, 1972; 34:187-220. 13. Dixon WJ, ed. BMDP Statistical Software. University of California Press, 1985. 14. Traverso CE, Spaeth GL, Starita RJ, et al. Factors affecting the results of argon laser trabeculoplasty in open-angle glaucoma. Ophthalmic Surg 1986; 17:554-9.
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15. Brown SVL, Thomas JV, Budenz DL, et al. Effect of cataract surgery on intraocular pressure reduction obtained with laser trabeculoplasty. Am J Ophthalmol1985; 100:373-6.
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16. Pollack IP, Robin AL, Sax H. The effect of argon laser trabeculoplasty on the medical control of primary open-angle glaucoma. Ophthalmology 1983; 90:785-9.
Discussion
by
Douglas R. Anderson, MD Shingleton and co-workers have brought us up-to-date on long-term results of argon laser trabeculoplasty. To judge whether the outcome is good or bad, we of course compare the results with what we think would have happened with some alternate management (i.e., continued full medical therapy with suboptimal pressure, or trabeculectomy with its attendant better pressure control but also additional expense and risk of complication). Ideally, we might hope for some randomized prospective trial comparing argon laset trabeculoplasty with one or another alternate, but such data are lacking, and we must see what we can conclude about argon laser trabeculoplasty with the available information. First, argon laser trabeculoplasty does lower intraocular pressure (lOP) in the majority of patients treated. Some enjoy pressure lowering without the need for continued medication, but many must continue at least some of their medications. Separate from these prompt "successes" are 20 to 25% who, practically from the start, had inadequate lowering ofiOP and therefore undergo a second laser treatment or surgery within 1 year (a second laser treatment usually did not work, and all but 4 of 15 such patients subsequently required filtration surgery)_ From among the 75 to 80% who did not suffer prompt failure, most maintained a controlled pressure with stable discs and fields for the duration of follow-up. However, some later failed in one of three ways. A very few had partial lowering of pressure, and the surgeon deferred judgment for more than I year before finally deciding that the pressure was still worrisome and that it was prudent to perform surgery. More often, the pressure increased after initial adequate lowering of pressure, and for that reason further intervention was required. A third type of late failure was represented by five cases of progressive change in disc or field (or both), four of which did so despite normal lOP. In total, through one of these three courses, the late failures occurred at a rate of 10% (of the remaining successes) per year. Thus, a 75% success at 1 year is reduced to 50% success by the end of 5 years.
From the Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami. Supported in part by the National Glaucoma Research, a program of American Health Assistance Foundation, Rockville, Maryland. Reprint requests to Douglas R. Anderson, MD, Bascom Palmer Eye Institute, PO Box 016880, Miami, FL 33101.
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One might hope for better results, but after 5 years at least half of the patients had avoided surgery. That benefit is seemingly enough to confirm our belief that argon laser trabeculoplasty should be done first whenever medical therapy has failed and surgery is the only other alternative-unless you believe that the group would have been better off if all had filtration surgery. This would be true, for example, if delay in the unsuccessful laser cases caused further visual loss to occur before the filtration surgery was done. Evidently, this does not occur. Five cases did have further nerve damage or field loss, but in only one case did this occur because of inadequate pressure lowering. (One must trust that indications for argon laser trabeculoplasty were such that field loss would have occurred without intervention in substantially more than 5 cases). Thus, the following two conclusions may be reached. (I) The occurrence of nerve damage and field loss is reduced by the use of argon laser trabeculoplasty in cases with apparently inadequate response to medical therapy. One might like a randomized clinical trial in which half of such patients are followed as a comparison group without intervention in order to establish that the intervention definitely results in a lower incidence of field loss. However, one would have to be far off in clinical judgment of when argon laser trabeculoplasty is indicated for the nonintervention group to have only a 5% incidence of field loss. (2) Primary use of argon laser trabeculoplasty followed by trabeculectomy in selected cases is a better strategy than prompt filtration surgery for all cases. Filtration surgery does seem more often to achieve lower lOP without the need for continued medication, but again, one might hope for a randomized trial comparing these two alternatives in order to be sure. However, our collective clinical judgment currently might be that cataract formation, longer postoperative recovery, and occasional disasterous results might too high a price to pay: the current strategy reduces field loss to 5% and elimination of that 5% risk is the most benefit that the surgery-in-all-cases strategy could achieve. Moreover, we know that surgery too has a certain rate oflate failure to control the lOP. Therefore, the current data suggest that the strategy of using laser before surgery is on track.