- Email: [email protected]
Argon vs Diode Laser Trabeculoplasty
Argon vs Diode Laser Trabeculoplasty JUDITH A. ENGLERT, MD, TERRY A. COX, MD, R. RAND ALLINGHAM, MD, AND M. BRUCE SHIELDS, MD
• PURPOSE: To compare the efficacy of diode laser and argon laser trabeculoplasty in a randomized prospective study of 11 paired fellow eyes. • METHODS: Fellow eyes of 11 patients, having had no prior laser trabeculoplasty and requiring laser trabeculoplasty to lower intraocular pres sure, were randomly assigned prospectively to diode laser trabeculoplasty in one eye and argon laser trabeculoplasty in the other eye. • RESULTS: In the diode laser group, the average baseline intraocular pressure was 21.6 ± 2.0 mm Hg before trabeculoplasty and 19.6 ± 2 . 1 mm Hg (or a 7.7% ± 11.5% mean pressure reduction) at 1 month, 19.3 ± 2.6 mm Hg (or a 6.9% ± 13.5% mean reduction) at 2 months, and 19.0 ± 3 . 3 mm Hg (or a 2.4% ± 16.9% mean reduction) at 3 months postoperatively. In the argon laser group, the average intraocular pressure was 24.4 ± 3 . 5 mm Hg before treatment and 17.6 ± 1.7 mm Hg (or a 24.7% ± 11.4% mean pressure reduction) at 1 month, 16.8 ± 2.5 mm Hg (or a 26.7% ± 15.3% mean reduction) at 2 months, and 15.5 ± 1.2 mm Hg (or a 30.0% ± 16.5% mean reduc tion) at 3 months after laser trabeculoplasty. The difference between argon and diode laser intraocu lar pressure reduction was statistically significant at 1 month (P < .01), 2 months (P < .01), and 3 months (P < .05) after treatment. • CONCLUSION: Argon laser trabeculoplasty ap pears to be more effective than diode laser therapy in lowering intraocular pressure during the first 3 months after treatment. Accepted for publication March 6, 1997. From the Department of Ophthalmology, Duke University Medical Center, Durham, North Carolina (Drs Englert, Cox, and Allingham), and the Department of Ophthalmology, Yale University, New Haven, Connecticut (Dr Shields). Reprint requests to R. Rand Allingham, MD, Duke University Eye Center, Box 3802, Durham, NC 27710; fax: (919) 681-6474.
VOL.124, N O . 5
A
RGON
LASER TRABECULOPLASTY HAS BEEN
used to treat open-angle glaucoma since 1979.1 Pressure-lowering effects can also be achieved with other laser wavelengths, including krypton red at 647 nm2 and Nd:YAG laser at 1,064 nm.3 A recent innovation in ophthalmology is the diode laser, which emits infrared energy at a wave length of 790 to 850 nm. Laser trabeculoplasty by means of an infrared wavelength may have several clinical advantages over surgery using the argon laser, which has a shorter wavelength. Advantages include less disruption of the blood-aqueous barrier, less formation of peripheral anterior synechiae, less pain associated with the procedure, fewer intraocular pres sure spikes after treatment, arid less postoperative inflammation.4 Technically, the diode laser also has several advantages over argon laser units, including smaller size, more portability, and reduced expense.5 We compared the efficacy of argon and diode laser trabeculoplasty in reducing intraocular pressure in paired fellow eyes of 11 patients with medically uncontrolled open-angle glaucoma.
PATIENTS AND METHODS ELEVEN PATIENTS HAVING 22 PAIRED FELLOW EYES WITH
medically uncontrolled open-angle glaucoma were enrolled in the study after providing informed con sent. The study was approved by the institutional review board. Patients with a type of glaucoma known to be responsive to laser trabeculoplasty and having had no prior laser trabeculoplasty were considered for the study. Fourteen patients were initially enrolled and were randomly assigned prospectively to receive argon laser trabeculoplasty in one eye and diode laser trabeculoplasty in the other eye. Three of the 14 patients required laser trabeculoplasty in one eye only
© AMERICAN JOURNAL OF OPHTHALMOLOGY 1997;124:627-631
627
during the period of the study and were thus excluded from analysis. The 11 remaining patients were composed of two men and nine women with an age range of 57 to 81 years. Ten patients were white and one patient was African American (Patient 7). Ten patients had chronic open-angle glaucoma, and one had the exfoliation syndrome with associated glaucoma (Pa tient 1). Ten months before enrollment in the study, Patient 9 underwent bilateral peripheral iridectomies for open but narrow angles and had no documented episode of angle-closure glaucoma or evidence of peripheral anterior synechiae on examination. One eye of each subject was randomly assigned to trabeculoplasty by means of an argon laser with a wavelength of 488 to 514 nm (VISULAS Argon II, Carl Zeiss Instruments, Oberkochen, Germany) using a 50-(xm spot size, 0.1-second duration, and an average power of 1.0 W directed through an antireflection-coated Goldmann lens. Approximately 50 burns were applied to the anterior portion of the trabecular meshwork in the nasal 180 degrees. The fellow eye of each subject received trabeculoplasty by means of a diode laser with a wavelength of 790 to 850 nm (OcuLight SLx, IRIS Medical Instruments, Mountain View, California) using a 75-u,m spot, 0.1-second duration, and a power of 1.0 to 1.2 W directed through a Ritch trabeculoplasty lens. The Ritch lens is a 17-diopter plano-convex lens that provides Xl.4 magnification,6 reducing the effective spot size from 75 to 52.5 (xm and thus providing a more comparable spot size between the two laser units. The same number and placement of laser applications was used as with the argon laser, and power was adjusted with both instruments to provide a mild, visible tissue reaction. With the argon, the reaction was usually a blanching of the trabecular meshwork with occasional gas bubble formation, whereas only a faint blanching or tissue movement was typically seen with the diode laser. Two of us (M.B.S., R.R.A) performing the laser trabeculoplasty were equally skilled in performance of trabeculoplasty using either laser system. The author performing trabeculoplasty on the first eye of each patient also performed laser trabeculoplasty on the other eye of that patient to control for potential variation in technique. Postoperatively, one drop of apraclonidine 0.5% 628
was administered. Intraocular pressure was measured by ophthalmic technicians masked to patient partici pation in the study. Intraocular pressure was measured at 1 hour after treatment. A pressure spike of greater than 5 mm Hg occurred 1 hour postoperatively in the argon-treated eye of Patient 5 and in the diode-treated eye of Patient 6 (Table 1). These two patients were treated with additional pressure-lowering agents as required, and the pressure was rechecked the follow ing day. The treated eye of each of these patients had an intraocular pressure lower than the baseline pres sure 1 day after treatment, and any additional ocular hypotensives were stopped. Fluorometholone 0.1% drops were given four times a day for 5 days postoper atively to all patients. Patients were also evaluated at 1 month, 2 months, and 3 months after treatment. At each visit, intraocu lar pressure was recorded. Medications between mea surements were unchanged in all cases. When a patient required either an alteration of medication regimen or an additional laser procedure in either eye, that patient was excluded from further analysis at that point. Data were analyzed using both parametric (paired t test) and nonparametric (Wilcoxon signed-rank test) techniques, with outcomes expressed as both absolute change and percent change from baseline. Because the results were similar in all four cases, only t tests on absolute change in intraocular pressure are reported.
RESULTS THE INITIAL AVERAGE INTRAOCULAR PRESSURE WAS 24.4
± 3 . 5 mm Hg in the argon-treated eyes and 21.6 ± 2.0 mm Hg in the diode-treated eyes, as shown in the Figure. The difference between the baseline intraocu lar pressure measurements in the two groups was not significant (P = .096). Measurements obtained 1 hour after treatment were higher with argon laser than were those obtained after treatment with diode laser (Table 1), although the results were not statisti cally significant (P = .16). Although observations were not statistically evalu ated, no difference in postoperative inflammation as estimated by slit-lamp examination was apparent between the two groups. Nearly all of the patients voiced a preference for diode laser over argon laser
AMERICAN JOURNAL OF OPHTHALMOLOGY
NOVEMBER 1997
TABLE 1. Intraocular Pressures of Individual Patients After Laser Trabeculoplasty*
Patient No.
1 2 3 4 5 6 7 8 9 10 11
Laser
Baseline Intraocular Pressure
Type
(mm Hg)
1 hr
1 mo
2 mos
3 mos
A D A D D A A D A D D A A D A D A D A D D A
40 25 27 26 19 23 28 23 24 25 19 22 21 17 19 17 22 25 18 21 21 24
+3 -3 0 -10 -1 -3
-23 -8 -13 -7 +1 -10 -9 -3 -7 -5 +2 -3 -2 -3 -3 0 -5 -6 0 0 +7 0
-25 -8 -15 -8 -1 -10
-24 -8
Change in Intraocular Pressure (mm Hg)f
i-2
-3 + 16 -5 +7 -1 -4 -5 -4 +1 +2 -3 +4 -6 +1 -4
— —
— — -1 -9
— — — —
-6 -5 +1 -3 -6 -3 -3 0
+5 -8 -6 -3 -3 0
— —
— —
0 +1 +7 +1
0 +3
— —
A = argon laser; D = diode laser. The first line listed for each patient represents the right eye. A dash indicates that the patient was eliminated from further analysis. ♦A positive number indicates an increase and a negative number, a decrease.
because of increased intraoperative comfort, although responses were not quantified. At the 1-month follow-up examination, the intraoc ular pressure dropped by an average of 6.8 ± 4.0 mm Hg from baseline (corresponding to a 24.7% ± 11.4% mean intraocular pressure reduction) in the argontreated eyes compared with a reduction of 2.0 ± 2.7 mm Hg, or a 7.7% ± 11.5% mean pressure reduction in the diode-treated eyes, as shown in Table 2. Data were analyzed by comparing the difference in intraocular pressure reduction between the argontreated and diode-treated eye in each patient at the various time intervals postoperatively. Individual data for each subject at all time periods are shown in Table 1. Mean percent pressure reduction was calculated by determining the percent of pressure reduction for each patient and then averaging the individual per cent drops in pressure. At 1 month, there was a significant difference in change from baseline be tween the two groups (P = .010). Patient 4 required a VOL.124, No. 5
second trabeculoplasty to both the argon-treated eye and the diode-treated eye to reduce the intraocular pressure and was excluded from further analysis after 1 month. Patient 9 required a second trabeculoplasty to the diode-treated eye after 1 month and was also excluded from further analysis at that time. With nine subjects remaining at the 2-month follow-up examination, the average intraocular pres sure measurement was 16.8 ± 2.5 mm Hg, corre sponding to a 26.7% ± 15.3% mean intraocular pressure reduction in the argon-treated eyes, and 19.3 ± 2.6 mm Hg, or a 6.9% ± 13.5% mean intraocular pressure reduction, in the diode-treated group (Table 2); the difference in change from baseline was again statistically significant (P = .010). After this interval, Patients 2 and 5 required an additional pressurelowering agent for the diode-treated eye and were excluded from further analysis. Patient 11 required additional laser trabeculoplasties to both the argontreated and diode-treated eyes at that time.
ARGON VS DIODE LASER TRABECULOPLASTY
629
• Argon - « - ■ Diode
X.
"" * — 1
* I h-#-H
I
Time Aft«r Laser
FIGURE. Mean intraocular pressure measurements ± SEM after diode laser and argon laser trabeculoplasty.
TABLE 2. Change in Mean Intraocular Pressure After Laser Trabeculoplasty'" Change (rTim Hg)
n Baseline 1 mo 2 mos 3 mos
11 11 9 6
Argon Laser
24.4 -6.8 -7.4 -8.3
± ± ± ±
Diode Laser
3.5 4.0 5.4 6.7
21.6 -2.0 -1.8 -0.7
± ± ± ±
P Value (Paired t Test)
2.0 2.7 3.2 3.7
.0097 .0096 .0218
'Data are expressed as 95% confidence limits (mm Hg).
The six subjects remaining at the 3-month followup examination had an average intraocular pressure of 15.5 ± 1.2 mm Hg, corresponding to a 30.0% ± 16.5% mean intraocular pressure reduction, in the argon-treated eyes, and 19.0 ±3.3 mm Hg, or a 2.4% ± 16.9% mean pressure reduction, in the diodetreated eyes (Table 2). The difference in intraocular pressure response remained statistically significant (P = .022). At all monthly follow-up visits, the changes from baseline for argon-treated eyes were statistically signif icant when evaluated as a separate group (P = .008 at 1 month, P = .032 at 2 months, P = .016 at 3 months). The changes from baseline for diodetreated eyes were not statistically significant (P = .17 at 1 month, P = .30 at 2 months, P = .94 at 3 months). 630
DISCUSSION ARGON LASER TRABECULOPLASTY HAS BEEN SHOWN TO
be an effective method for lowering intraocular pres sure in numerous previous studies. McHugh and associates7 examined the efficacy of diode laser tra beculoplasty on 20 eyes of 13 patients with openangle glaucoma and found a mean ocular hypotensive effect of 9.30 mm Hg at 3 months from a mean baseline intraocular pressure of 28.30 mm Hg. Brancato and associates8 found no significant difference between the hypotensive effect of argon and diode laser trabeculoplasty on two groups of 10 different patients at 6 months and 1 year after treatment. The average pressure reduction at 6 months for diode laser was 6.7 mm Hg, or a 28.7% mean intraocular pressure reduction, and for argon laser, 5.8 mm Hg, or a 25.9% mean drop in intraocular pressure. Moriarty and associates9 found a somewhat greater mean ocular hypotensive effect with diode laser of 9.32 mm Hg at 3 months from a mean baseline pressure of 26.9 mm Hg in 25 eyes of 16 patients. The 2-year follow-up of these patients showed that this hypotensive effect was maintained. None of the above studies was done with paired fellow eyes. A report by Brooks and Gillies10 found a mean hypotensive effect of 5 mm Hg with argon laser and 4 mm Hg with diode laser at 3 months when comparing 50 eyes of 50 patients undergoing argon or diode laser
AMERICAN JOURNAL OF OPHTHALMOLOGY
NOVEMBER 1997
trabeculoplasty. Twenty-three paired fellow eyes were then evaluated to determine whether argon was more effective than diode; in this group, argon laser trabec uloplasty lowered intraocular pressure by 5 mm Hg, whereas trabeculoplasty using the diode laser lowered intraocular pressure by 3 mm Hg. Evaluating the group of paired fellow eyes by the Wilcoxon signedrank test showed a statistically significant difference between the efficacy of argon compared with that of diode laser trabeculoplasty. Our findings in this study showing better efficacy with argon than with diode laser for trabeculoplasty are similar to those of Brooks and Gillies10 when analyzing paired fellow eyes. We found a significant difference in ocular hypotensive effect at 1 month, 2 months, and 3 months when comparing diode and argon laser in paired fellow eyes. Variables such as age, race, and trabecular pigmentation were inherently controlled by comparing fellow eyes of the same patient. Admittedly, patients with the exfoliation syndrome may have asymmetric trabecular meshwork pigmentation. However, patients with this type of glaucoma were included in the study because it is a condition known to respond to laser trabeculoplasty, and the eyes were randomly assigned to each type of laser to prevent bias. Statistical analysis that excluded the exfoliation patient still showed argon laser trabec uloplasty to be significantly more effective than diode laser (P < .05 for each of the various follow-up periods). Settings were essentially the same for both types of laser, with perhaps slightly more power per square area of trabecular meshwork using the diode. These settings were nearly identical to those used in prior studies in which large numbers of patients demonstrated efficacy of diode laser trabeculoplasty.7'9 We did not carry out analysis beyond 3 months postoperatively; however, previous studies7'9 do show that this hypotensive effect is maintained. Our study specifically addresses the comparison of
efficacy between the two treatment modalities for laser trabeculoplasty rather than the overall efficacy of either one of the laser types. Because we compared fellow eyes, we were able to use a smaller sample size to answer this specific question. It would be erroneous to conclude from this study that diode laser is ineffective in reducing intraocular pressure. In fact, diode laser did reduce intraocular pressure in our small series of patients, although not to the degree found by other authors.7'9 We conclude that argon laser does appear to be significantly more effective than diode laser in reducing intraocular pressure in the early postopera tive period.
REFERENCES 1. Wise JB, Witter SL. Argon laser therapy for open-angle glaucoma. Arch Ophthalmol 1979;97:319-322. 2. Spumy RC, Lederer CM Jr. Krypton laser trabeculoplasty: a clinical report. Arch Ophthalmol 1984;102:1626-1628. 3. Belgrado G, Brihaye-Van Geertruyden M, Herzeel R. Com parison of argon and cw.Nd.YAG laser trabeculoplasty: clinical results. In: Marshall J, editor. Laser technology in ophthalmology. Berkeley: Kugler and Ghedini, 1988:45-52. 4. Moriarty AP, McHugh JDA, Spalton DJ, ffytche TJ, Shah SM, Marshall J. Comparison of the anterior chamber inflammatory response to diode and argon laser trabecul oplasty using a laser flare meter. Ophthalmology 1993; 100: 1263-1267. 5. Moriarty AP. Diode lasers in ophthalmology. Int Ophthal mol 1993;17:297-304. 6. Ritch R. A new lens for argon laser trabeculoplasty. Oph thalmic Surg 1985;16:331-332. 7. McHugh D, Marshall J, ffytche TJ, Hamilton PAM, Raven A. Diode laser trabeculoplasty (DLT) for primary open-angle glaucoma and ocular hypertension. Br J Ophthalmol 1990; 74:743-747. 8. Brancato R, Carassa R, Trabucchi G. Diode laser compared with argon laser for trabeculoplasty. Am J Ophthalmol 1991;112:50-55. 9. Moriarty AP, McHugh JDA, ffytche TJ, Marshall J, Hamil ton PAM. Long-term follow-up of diode laser trabeculoplasty for primary open-angle glaucoma and ocular hypertension. Ophthalmology 1993;100:1614-1618. 10. Brooks AMV, Gillies WE. Laser trabeculoplasty: argon or diode? Aust N Z J Ophthalmol 1992;21:161-164.
Authors Interactive™ Comments and questions regarding this article may be addressed to authors via THE JOURNAL'S Web Site. Selected comments, questions, and author responses are posted on Authors Interactive™ at http://www.ajo.com/
VOL.124, No. 5
ARGON VS DIODE LASER TRABECULOPLASTY
631
• PURPOSE: To compare the efficacy of diode laser and argon laser trabeculoplasty in a randomized prospective study of 11 paired fellow eyes. • METHODS: Fellow eyes of 11 patients, having had no prior laser trabeculoplasty and requiring laser trabeculoplasty to lower intraocular pres sure, were randomly assigned prospectively to diode laser trabeculoplasty in one eye and argon laser trabeculoplasty in the other eye. • RESULTS: In the diode laser group, the average baseline intraocular pressure was 21.6 ± 2.0 mm Hg before trabeculoplasty and 19.6 ± 2 . 1 mm Hg (or a 7.7% ± 11.5% mean pressure reduction) at 1 month, 19.3 ± 2.6 mm Hg (or a 6.9% ± 13.5% mean reduction) at 2 months, and 19.0 ± 3 . 3 mm Hg (or a 2.4% ± 16.9% mean reduction) at 3 months postoperatively. In the argon laser group, the average intraocular pressure was 24.4 ± 3 . 5 mm Hg before treatment and 17.6 ± 1.7 mm Hg (or a 24.7% ± 11.4% mean pressure reduction) at 1 month, 16.8 ± 2.5 mm Hg (or a 26.7% ± 15.3% mean reduction) at 2 months, and 15.5 ± 1.2 mm Hg (or a 30.0% ± 16.5% mean reduc tion) at 3 months after laser trabeculoplasty. The difference between argon and diode laser intraocu lar pressure reduction was statistically significant at 1 month (P < .01), 2 months (P < .01), and 3 months (P < .05) after treatment. • CONCLUSION: Argon laser trabeculoplasty ap pears to be more effective than diode laser therapy in lowering intraocular pressure during the first 3 months after treatment. Accepted for publication March 6, 1997. From the Department of Ophthalmology, Duke University Medical Center, Durham, North Carolina (Drs Englert, Cox, and Allingham), and the Department of Ophthalmology, Yale University, New Haven, Connecticut (Dr Shields). Reprint requests to R. Rand Allingham, MD, Duke University Eye Center, Box 3802, Durham, NC 27710; fax: (919) 681-6474.
VOL.124, N O . 5
A
RGON
LASER TRABECULOPLASTY HAS BEEN
used to treat open-angle glaucoma since 1979.1 Pressure-lowering effects can also be achieved with other laser wavelengths, including krypton red at 647 nm2 and Nd:YAG laser at 1,064 nm.3 A recent innovation in ophthalmology is the diode laser, which emits infrared energy at a wave length of 790 to 850 nm. Laser trabeculoplasty by means of an infrared wavelength may have several clinical advantages over surgery using the argon laser, which has a shorter wavelength. Advantages include less disruption of the blood-aqueous barrier, less formation of peripheral anterior synechiae, less pain associated with the procedure, fewer intraocular pres sure spikes after treatment, arid less postoperative inflammation.4 Technically, the diode laser also has several advantages over argon laser units, including smaller size, more portability, and reduced expense.5 We compared the efficacy of argon and diode laser trabeculoplasty in reducing intraocular pressure in paired fellow eyes of 11 patients with medically uncontrolled open-angle glaucoma.
PATIENTS AND METHODS ELEVEN PATIENTS HAVING 22 PAIRED FELLOW EYES WITH
medically uncontrolled open-angle glaucoma were enrolled in the study after providing informed con sent. The study was approved by the institutional review board. Patients with a type of glaucoma known to be responsive to laser trabeculoplasty and having had no prior laser trabeculoplasty were considered for the study. Fourteen patients were initially enrolled and were randomly assigned prospectively to receive argon laser trabeculoplasty in one eye and diode laser trabeculoplasty in the other eye. Three of the 14 patients required laser trabeculoplasty in one eye only
© AMERICAN JOURNAL OF OPHTHALMOLOGY 1997;124:627-631
627
during the period of the study and were thus excluded from analysis. The 11 remaining patients were composed of two men and nine women with an age range of 57 to 81 years. Ten patients were white and one patient was African American (Patient 7). Ten patients had chronic open-angle glaucoma, and one had the exfoliation syndrome with associated glaucoma (Pa tient 1). Ten months before enrollment in the study, Patient 9 underwent bilateral peripheral iridectomies for open but narrow angles and had no documented episode of angle-closure glaucoma or evidence of peripheral anterior synechiae on examination. One eye of each subject was randomly assigned to trabeculoplasty by means of an argon laser with a wavelength of 488 to 514 nm (VISULAS Argon II, Carl Zeiss Instruments, Oberkochen, Germany) using a 50-(xm spot size, 0.1-second duration, and an average power of 1.0 W directed through an antireflection-coated Goldmann lens. Approximately 50 burns were applied to the anterior portion of the trabecular meshwork in the nasal 180 degrees. The fellow eye of each subject received trabeculoplasty by means of a diode laser with a wavelength of 790 to 850 nm (OcuLight SLx, IRIS Medical Instruments, Mountain View, California) using a 75-u,m spot, 0.1-second duration, and a power of 1.0 to 1.2 W directed through a Ritch trabeculoplasty lens. The Ritch lens is a 17-diopter plano-convex lens that provides Xl.4 magnification,6 reducing the effective spot size from 75 to 52.5 (xm and thus providing a more comparable spot size between the two laser units. The same number and placement of laser applications was used as with the argon laser, and power was adjusted with both instruments to provide a mild, visible tissue reaction. With the argon, the reaction was usually a blanching of the trabecular meshwork with occasional gas bubble formation, whereas only a faint blanching or tissue movement was typically seen with the diode laser. Two of us (M.B.S., R.R.A) performing the laser trabeculoplasty were equally skilled in performance of trabeculoplasty using either laser system. The author performing trabeculoplasty on the first eye of each patient also performed laser trabeculoplasty on the other eye of that patient to control for potential variation in technique. Postoperatively, one drop of apraclonidine 0.5% 628
was administered. Intraocular pressure was measured by ophthalmic technicians masked to patient partici pation in the study. Intraocular pressure was measured at 1 hour after treatment. A pressure spike of greater than 5 mm Hg occurred 1 hour postoperatively in the argon-treated eye of Patient 5 and in the diode-treated eye of Patient 6 (Table 1). These two patients were treated with additional pressure-lowering agents as required, and the pressure was rechecked the follow ing day. The treated eye of each of these patients had an intraocular pressure lower than the baseline pres sure 1 day after treatment, and any additional ocular hypotensives were stopped. Fluorometholone 0.1% drops were given four times a day for 5 days postoper atively to all patients. Patients were also evaluated at 1 month, 2 months, and 3 months after treatment. At each visit, intraocu lar pressure was recorded. Medications between mea surements were unchanged in all cases. When a patient required either an alteration of medication regimen or an additional laser procedure in either eye, that patient was excluded from further analysis at that point. Data were analyzed using both parametric (paired t test) and nonparametric (Wilcoxon signed-rank test) techniques, with outcomes expressed as both absolute change and percent change from baseline. Because the results were similar in all four cases, only t tests on absolute change in intraocular pressure are reported.
RESULTS THE INITIAL AVERAGE INTRAOCULAR PRESSURE WAS 24.4
± 3 . 5 mm Hg in the argon-treated eyes and 21.6 ± 2.0 mm Hg in the diode-treated eyes, as shown in the Figure. The difference between the baseline intraocu lar pressure measurements in the two groups was not significant (P = .096). Measurements obtained 1 hour after treatment were higher with argon laser than were those obtained after treatment with diode laser (Table 1), although the results were not statisti cally significant (P = .16). Although observations were not statistically evalu ated, no difference in postoperative inflammation as estimated by slit-lamp examination was apparent between the two groups. Nearly all of the patients voiced a preference for diode laser over argon laser
AMERICAN JOURNAL OF OPHTHALMOLOGY
NOVEMBER 1997
TABLE 1. Intraocular Pressures of Individual Patients After Laser Trabeculoplasty*
Patient No.
1 2 3 4 5 6 7 8 9 10 11
Laser
Baseline Intraocular Pressure
Type
(mm Hg)
1 hr
1 mo
2 mos
3 mos
A D A D D A A D A D D A A D A D A D A D D A
40 25 27 26 19 23 28 23 24 25 19 22 21 17 19 17 22 25 18 21 21 24
+3 -3 0 -10 -1 -3
-23 -8 -13 -7 +1 -10 -9 -3 -7 -5 +2 -3 -2 -3 -3 0 -5 -6 0 0 +7 0
-25 -8 -15 -8 -1 -10
-24 -8
Change in Intraocular Pressure (mm Hg)f
i-2
-3 + 16 -5 +7 -1 -4 -5 -4 +1 +2 -3 +4 -6 +1 -4
— —
— — -1 -9
— — — —
-6 -5 +1 -3 -6 -3 -3 0
+5 -8 -6 -3 -3 0
— —
— —
0 +1 +7 +1
0 +3
— —
A = argon laser; D = diode laser. The first line listed for each patient represents the right eye. A dash indicates that the patient was eliminated from further analysis. ♦A positive number indicates an increase and a negative number, a decrease.
because of increased intraoperative comfort, although responses were not quantified. At the 1-month follow-up examination, the intraoc ular pressure dropped by an average of 6.8 ± 4.0 mm Hg from baseline (corresponding to a 24.7% ± 11.4% mean intraocular pressure reduction) in the argontreated eyes compared with a reduction of 2.0 ± 2.7 mm Hg, or a 7.7% ± 11.5% mean pressure reduction in the diode-treated eyes, as shown in Table 2. Data were analyzed by comparing the difference in intraocular pressure reduction between the argontreated and diode-treated eye in each patient at the various time intervals postoperatively. Individual data for each subject at all time periods are shown in Table 1. Mean percent pressure reduction was calculated by determining the percent of pressure reduction for each patient and then averaging the individual per cent drops in pressure. At 1 month, there was a significant difference in change from baseline be tween the two groups (P = .010). Patient 4 required a VOL.124, No. 5
second trabeculoplasty to both the argon-treated eye and the diode-treated eye to reduce the intraocular pressure and was excluded from further analysis after 1 month. Patient 9 required a second trabeculoplasty to the diode-treated eye after 1 month and was also excluded from further analysis at that time. With nine subjects remaining at the 2-month follow-up examination, the average intraocular pres sure measurement was 16.8 ± 2.5 mm Hg, corre sponding to a 26.7% ± 15.3% mean intraocular pressure reduction in the argon-treated eyes, and 19.3 ± 2.6 mm Hg, or a 6.9% ± 13.5% mean intraocular pressure reduction, in the diode-treated group (Table 2); the difference in change from baseline was again statistically significant (P = .010). After this interval, Patients 2 and 5 required an additional pressurelowering agent for the diode-treated eye and were excluded from further analysis. Patient 11 required additional laser trabeculoplasties to both the argontreated and diode-treated eyes at that time.
ARGON VS DIODE LASER TRABECULOPLASTY
629
• Argon - « - ■ Diode
X.
"" * — 1
* I h-#-H
I
Time Aft«r Laser
FIGURE. Mean intraocular pressure measurements ± SEM after diode laser and argon laser trabeculoplasty.
TABLE 2. Change in Mean Intraocular Pressure After Laser Trabeculoplasty'" Change (rTim Hg)
n Baseline 1 mo 2 mos 3 mos
11 11 9 6
Argon Laser
24.4 -6.8 -7.4 -8.3
± ± ± ±
Diode Laser
3.5 4.0 5.4 6.7
21.6 -2.0 -1.8 -0.7
± ± ± ±
P Value (Paired t Test)
2.0 2.7 3.2 3.7
.0097 .0096 .0218
'Data are expressed as 95% confidence limits (mm Hg).
The six subjects remaining at the 3-month followup examination had an average intraocular pressure of 15.5 ± 1.2 mm Hg, corresponding to a 30.0% ± 16.5% mean intraocular pressure reduction, in the argon-treated eyes, and 19.0 ±3.3 mm Hg, or a 2.4% ± 16.9% mean pressure reduction, in the diodetreated eyes (Table 2). The difference in intraocular pressure response remained statistically significant (P = .022). At all monthly follow-up visits, the changes from baseline for argon-treated eyes were statistically signif icant when evaluated as a separate group (P = .008 at 1 month, P = .032 at 2 months, P = .016 at 3 months). The changes from baseline for diodetreated eyes were not statistically significant (P = .17 at 1 month, P = .30 at 2 months, P = .94 at 3 months). 630
DISCUSSION ARGON LASER TRABECULOPLASTY HAS BEEN SHOWN TO
be an effective method for lowering intraocular pres sure in numerous previous studies. McHugh and associates7 examined the efficacy of diode laser tra beculoplasty on 20 eyes of 13 patients with openangle glaucoma and found a mean ocular hypotensive effect of 9.30 mm Hg at 3 months from a mean baseline intraocular pressure of 28.30 mm Hg. Brancato and associates8 found no significant difference between the hypotensive effect of argon and diode laser trabeculoplasty on two groups of 10 different patients at 6 months and 1 year after treatment. The average pressure reduction at 6 months for diode laser was 6.7 mm Hg, or a 28.7% mean intraocular pressure reduction, and for argon laser, 5.8 mm Hg, or a 25.9% mean drop in intraocular pressure. Moriarty and associates9 found a somewhat greater mean ocular hypotensive effect with diode laser of 9.32 mm Hg at 3 months from a mean baseline pressure of 26.9 mm Hg in 25 eyes of 16 patients. The 2-year follow-up of these patients showed that this hypotensive effect was maintained. None of the above studies was done with paired fellow eyes. A report by Brooks and Gillies10 found a mean hypotensive effect of 5 mm Hg with argon laser and 4 mm Hg with diode laser at 3 months when comparing 50 eyes of 50 patients undergoing argon or diode laser
AMERICAN JOURNAL OF OPHTHALMOLOGY
NOVEMBER 1997
trabeculoplasty. Twenty-three paired fellow eyes were then evaluated to determine whether argon was more effective than diode; in this group, argon laser trabec uloplasty lowered intraocular pressure by 5 mm Hg, whereas trabeculoplasty using the diode laser lowered intraocular pressure by 3 mm Hg. Evaluating the group of paired fellow eyes by the Wilcoxon signedrank test showed a statistically significant difference between the efficacy of argon compared with that of diode laser trabeculoplasty. Our findings in this study showing better efficacy with argon than with diode laser for trabeculoplasty are similar to those of Brooks and Gillies10 when analyzing paired fellow eyes. We found a significant difference in ocular hypotensive effect at 1 month, 2 months, and 3 months when comparing diode and argon laser in paired fellow eyes. Variables such as age, race, and trabecular pigmentation were inherently controlled by comparing fellow eyes of the same patient. Admittedly, patients with the exfoliation syndrome may have asymmetric trabecular meshwork pigmentation. However, patients with this type of glaucoma were included in the study because it is a condition known to respond to laser trabeculoplasty, and the eyes were randomly assigned to each type of laser to prevent bias. Statistical analysis that excluded the exfoliation patient still showed argon laser trabec uloplasty to be significantly more effective than diode laser (P < .05 for each of the various follow-up periods). Settings were essentially the same for both types of laser, with perhaps slightly more power per square area of trabecular meshwork using the diode. These settings were nearly identical to those used in prior studies in which large numbers of patients demonstrated efficacy of diode laser trabeculoplasty.7'9 We did not carry out analysis beyond 3 months postoperatively; however, previous studies7'9 do show that this hypotensive effect is maintained. Our study specifically addresses the comparison of
efficacy between the two treatment modalities for laser trabeculoplasty rather than the overall efficacy of either one of the laser types. Because we compared fellow eyes, we were able to use a smaller sample size to answer this specific question. It would be erroneous to conclude from this study that diode laser is ineffective in reducing intraocular pressure. In fact, diode laser did reduce intraocular pressure in our small series of patients, although not to the degree found by other authors.7'9 We conclude that argon laser does appear to be significantly more effective than diode laser in reducing intraocular pressure in the early postopera tive period.
REFERENCES 1. Wise JB, Witter SL. Argon laser therapy for open-angle glaucoma. Arch Ophthalmol 1979;97:319-322. 2. Spumy RC, Lederer CM Jr. Krypton laser trabeculoplasty: a clinical report. Arch Ophthalmol 1984;102:1626-1628. 3. Belgrado G, Brihaye-Van Geertruyden M, Herzeel R. Com parison of argon and cw.Nd.YAG laser trabeculoplasty: clinical results. In: Marshall J, editor. Laser technology in ophthalmology. Berkeley: Kugler and Ghedini, 1988:45-52. 4. Moriarty AP, McHugh JDA, Spalton DJ, ffytche TJ, Shah SM, Marshall J. Comparison of the anterior chamber inflammatory response to diode and argon laser trabecul oplasty using a laser flare meter. Ophthalmology 1993; 100: 1263-1267. 5. Moriarty AP. Diode lasers in ophthalmology. Int Ophthal mol 1993;17:297-304. 6. Ritch R. A new lens for argon laser trabeculoplasty. Oph thalmic Surg 1985;16:331-332. 7. McHugh D, Marshall J, ffytche TJ, Hamilton PAM, Raven A. Diode laser trabeculoplasty (DLT) for primary open-angle glaucoma and ocular hypertension. Br J Ophthalmol 1990; 74:743-747. 8. Brancato R, Carassa R, Trabucchi G. Diode laser compared with argon laser for trabeculoplasty. Am J Ophthalmol 1991;112:50-55. 9. Moriarty AP, McHugh JDA, ffytche TJ, Marshall J, Hamil ton PAM. Long-term follow-up of diode laser trabeculoplasty for primary open-angle glaucoma and ocular hypertension. Ophthalmology 1993;100:1614-1618. 10. Brooks AMV, Gillies WE. Laser trabeculoplasty: argon or diode? Aust N Z J Ophthalmol 1992;21:161-164.
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