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   Table of Contents      
ORIGINAL ARTICLE
Year : 1997  |  Volume : 45  |  Issue : 2  |  Page : 109-113

Primary argon laser trabeculoplasty vs pilocarpine 2% in open angle glaucoma : Two years follow-up study


Department of Ophthalmology, Postgraduate Institute of Medical Education and Research, Chandigarh, India

Correspondence Address:
A Sharma
Department of Ophthalmology, Postgraduate Institute of Medical Education and Research, Chandigarh
India
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Source of Support: None, Conflict of Interest: None


PMID: 9475029

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  Abstract 

In a prospective study, the efficacy of argon laser trabeculoplasty (ALT) was evaluated and compared with pilocarpine 2% as primary treatment in newly diagnosed primary open angle glaucoma (POAG). Out of 38 patients with POAG included in this study, one eye each of 36 patients underwent ALT, and one eye each of 26 patients received pilocarpine 2% every 8 hours. The mean pre-treatment IOP was 25.484.13 mmHg in ALT group and 24.473.51 mmHg in the pilocarpine group. The mean post treatment IOP at 2 year follow was 18.22.55 mmHg in ALT group and 18.272.22 mmHg in the pilocarpine group. Post treatment IOP was significantly lower than pre-treatment IOP in both ALT and pilocarpine groups. The post treatment fall in IOP showed no significant difference in ALT versus pilocarpine 2% at various follow up intervals (p>0.05). This study showed equal efficacy of ALT and pilocarpine 2% as initial therapy of POAG.

Keywords: Laser trabeculoplasty, pilocarpine 2%, primary open angle glaucoma


How to cite this article:
Sharma A, Gupta A. Primary argon laser trabeculoplasty vs pilocarpine 2% in open angle glaucoma : Two years follow-up study. Indian J Ophthalmol 1997;45:109-13

How to cite this URL:
Sharma A, Gupta A. Primary argon laser trabeculoplasty vs pilocarpine 2% in open angle glaucoma : Two years follow-up study. Indian J Ophthalmol [serial online] 1997 [cited 2021 Feb 25];45:109-13. Available from: https://www.ijo.in/text.asp?1997/45/2/109/15007



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In primary open angle glaucoma (POAG), the intraocular pressure (IOP) is raised to a level which is not compatible with normal function of the eye. Raised IOP has been recognised as the single most important risk factor for progression of disc and visual field changes in POAG.[1],[2] Various treatment options in primary POAG aim at lowering the IOP to preserve visual function.[3] Initial medical therapy and later filtering surgery, has been the standard to lower IOP in POAG.[4],[5]

Wise and Witter introduced argon laser trabeculoplasty (ALT) in 1979.[6] ALT is considered an effective modality for lowering IOP in open angle glaucoma. ALT avoids inconvenience, compliance problems, side effects of medical therapy and risks of major intraocular surgery.[7] ALT is mostly considered when medical therapy has failed to keep IOP within the normal limits.[7] ALT as primary treatment in POAG has been evaluated in some of the studies.[8][9][10] The present prospective study aims at evaluation of efficacy of ALT and comparison with pilocarpine 2% therapy in the initial management of POAG.


  Patients and methods Top


Thirty eight patients at the ophthalmology outpatient of the Postgraduate Institute of Medical Education and Research, Chandigarh with recent diagnosis of POAG were entered into the study. Criteria for inclusion into the trial were as follows: (i) IOP more than 21 mmHg on two occasions or on the same at two hour intervals between 8.00 AM and 5.00 PM with Goldmann applanation tonometer (2) Cup-disc ratio greater than 0.4, pallor of neuroretinal rim and /or generalised thinning of neuroretinal rim, polar notching; (3) glaucomatous field loss using Topcon automated perimeter. Eye with the first of these three criteria along with either on both of the second and third criteria were included in this study. Gonioscopic examination was undertaken to demonstrate open angle in all cases included in this study. The eyes which had undergone glaucoma filtering surgery or cataract extraction were excluded from the study. All the patients underwent complete ophthalmological examination including recording of visual acuity, intraocular pressure by applanation tonometer, direct ophthalmoscopy, gonioscopy and visual field examination (glaucoma screening and nasal step) with Topcon automated perimeter. Visual field changes as generalised depression, isolated paracentral scotoma, arcuate scotoma and nasal step were considered for diagnosis of POAG. Once inclusion criteria for POAG had been satisfied one eye each of every patient was treated with ALT and the other eye with medical therapy, pilocarpine 2% every 8 hours. Patients with even numbers received ALT in the right eye and pilocarpine (2%) in the left eye and patients with odd numbers received ALT in the left eye and pilocarpine (2%) in the right eye. Treatment to both eyes was initiated simultaneously. In case of delay in performing ALT, pilocarpine 2% every 8 hours was started and later discontinued on the day ALT was performed.

Patients in the laser treated group underwent single treatment session consisting of 100 burns over 360 of anterior trabecular meshwork. A spot size of 50 μm, exposure time of 0.1 seconds and power of 0.8 to 1.2 W were used. Intraocular pressure were measured with applanation tonometer at 1, 2, 6 and 24 hours following ALT to detect early rise of IOP. Patients who could not be monitored for post ALT acute rise of IOP were given tablet acetazolamide 250mg every 8 hours.

Intraocular pressure, visual field, gonioscopy and optic disc evaluation were done at 3, 6, 12, 18 and 24 months follow up. Treatment was considered effective in controlling IOP if it had been reduced to less than 21 mm Hg at all follow-up visits from three months onwards. Patients with IOP recording of 21 mm of Hg were rechecked after one week. Patients with IOP recording of 20 mm of Hg were considered for day time IOP records at 2 hour intervals. In the event of failure, second line of treatment in the form of timolol maleate 0.5%, every 12 hours was instituted. Visual field charts (glaucoma screening and nasal steps) obtained at various follow-up intervals were compared with baseline to determine progression of field changes. Disc changes were considered to have progressed if cup-disc ratio had increased at least by 0.2 as compared to the baseline. Gonioscopy was done at 6 and 12 months to detect goniosynechiae and trabecular pigmentation.

The mean IOP values and fall of IOP in the two treatment groups were compared and statistical significance evaluated by using two sample 't' test. The IOP control with ALT and pilocarpine 2% was compared using life table Log Rank test[11] and Kaplan-Meier method.[12]


  Results Top


The mean age of the 38 patients in this study was 44.5 (range 28-56) years. Twenty four patients were male and 14 female. Thirty six eyes underwent ALT and 26 eyes received pilocarpine 2%, every 8 hours. Fourteen eyes were excluded from the study. Of these, 6 had undergone trabeculectomy, 3 cataract surgery, 3 had normal IOP with no glaucomatous cupping or field defects and 1 eye each had absolute glaucoma and phthisis bulbi.

The mean fall in IOP was 7.544.74 mmHg at 3 months and 5.853.46 mmHg at 24 months in the ALT group, and 6.364.26 mm Hg at 3 months and 6.213.02 mm Hg at 24 months in the Pilocarpine 2% group [Figure - 1]. The mean fall in IOP in the ALT and pilocarpine 2% groups at various follow-up intervals was not significantly different (p>0.05) [Table - 1].

Post ALT IOP at 1, 2, 4, 6 and 24 hours could be recorded in 22 eyes. In 14 eyes post ALT IOP could not be recorded as patients expressed inability to come at desired time intervals. Six out 22 eyes (27%) showed rise of IOP (>5 mmHg) during the first 24 hours. The mean IOP immediately before ALT in these 22 eyes was 23.84.46 mmHg. The mean post ALT early IOP was 20.83.54 mmHg at 1 hour, 20.54.47 mmHg at 2 hours, 19.6416.12 mmHg at 4 hours, 19.55.34 mmHg at 6 hours and 18.863.87 mmHg at 24 hours.

Kaplan-Meier survival showed that IOP was controlled with ALT in 92% at 3 months, 84% at 6 months, 76% at 12 months, 70% at 18 months, and 59% at 24 months. Pilocarpine 2% controlled IOP in 89% at 3 months, 74% at 6 months, 67% at 12 months, 67% at 18 months, and 58% at 24 months [Figure - 2]. There was no statistically significant difference in the IOP control between the ALT and pilocarpine 2% groups (> 0.9 with Logrank test). [Table - 2] shows the life table data for the two groups.

Pretreatment best corrected visual acuity of 62 eyes included in this study ranged from 6/9 to 6/5. Two of 36 eyes that underwent ALT and 3 of 26 eyes treated with pilocarpine 2% had 2 lines decrease in visual acuity due to early cataract changes during follow up. In the ALT group, in 4 out of 15 eyes with failed treatment, IOP was not controlled with additional timolol maleate 0.5% and showed progression in disc changes alongwith deterioration in visual fields. In the pilocarpine 2% group, in 3 out of 11 eyes with failed treatment, IOP was not controlled with additional timolol maleate 0.5% and showed deterioration of visual fields alongwith progression of disc changes. None of patients developed goniosynechiae following ALT, however, 6 of 23 (26%) eyes showed increased trabecular pigmentation.


  Discussion Top


Intraocular pressure has been recognised as the most significant risk factor associated with optic disc damage in primary POAG.[1] The present study evaluates and compares IOP lowering effect of ALT with pilocarpine 2% as initial therapy in POAG patients. ALT is considered an effective modality for lowering intraocular pressure. Most of the investigators consider ALT as an adjuvant to medical therapy.[7] ALT on an average reduced IOP by 6.4 mmHg (26%) at 5 months in 237 chronic open angle glaucoma patients.[8] In glaucoma laser trial, ALT reduced on an average 9 mm Hg (33%) IOP at 3 months follow up.[9] In another study a mean of 7.8 mmHg IOP reduction was reported following ALT.[10] In the present study, ALT resulted in significant lowering of IOP at 3, 6, 12,18 and 24 months follow up. The mean IOP lowering at various post ALT intervals ranged from 6.1 to 7.8 mmHg in the present study. These results are comparable to those reported in the literature.[8],[9]

In recent literature, the role of ALT as initial treatment in POAG has been evaluated and compared with medical or surgical treatment.[9],[10],[13] Primary ALT has been reported to be more effective than pilocarpine 4% in lowering IOP.[10] In a recent study, mean reduction of IOP was recorded in 60% with surgery, 48.5% with maximal medical treatment and 38% with laser therapy alone.[13] The glaucoma laser trial group (1990) reported that IOP lowering following ALT was 2 mmHg more than medical therapy.[9] In the glaucoma laser trial ALT alone controlled IOP in higher percentage of patients at 1 and 2 years (63% and 44%) than timolol maleate 0.5% alone (41 % and 30%). However the major concern in this study is lowering of IOP in ALT treated eyes due to cross over effect of timolol maleate 0.5%. Due to this reason we preferred pilocarpine 2% as primary medical therapy in the present study. The results of ALT in these prospective studies are either better than or equivalent to medical therapy in lowering IOP. In the present study ALT was found to be effective as primary treatment and IOP lowering effect was equivalent to medical treatment with pilocarpine 2%-76% and 59% success in the ALT group and 66% and 58% success in the Pilocarpine groups at 12 and 24 months, respecteively.

The efficacy of ALT is known to decrease with long-term follow up. Schwatz et al[14] reported that the success rate of 77% at 2 years decreased to 46% at 5 years. Spaeth and Baez[15] reported that 33% of patients with POAG treated with ALT are controlled at 5 years. Maximum failures occur in the first year and subsequently success decreases at the rate of 10% per year.[7] In the present study success rate decreased from 76% at 12 months to 59% at 24 months.

Argon laser trabeculoplasty is safe and no serious complications have been reported following this procedure.[7] The only complication of concern following ALT is post treatment acute elevation of intraocular pressure.[7] Post ALT rise of IOP more than 5 mmHg has been reported in 34% and >10 mmHg in 12% patients.[16] Six of 22 (27%) eyes showed acute post ALT rise of IOP >5 mmHg in the first 24 hours in our study. The post laser rise of IOP can be reduced by acetazolamide 250 mg 8 hourly or use of clonidine derivatives topically.[17]

The authors are aware of the concern over preferring pilocarpine 2% as initial therapy. Currently beta-blockers such as timolol maleate 0.5% and betaxolol 0.5% are preferred as initial therapy for treatment of primary open angle glaucoma patients. However, the results of this study indicate that the effect of ALT on lowering IOP is at least equivalent to a single drug. As this study design included patients a POAG only separate studies would be needed to evaluate the efficacy of ALT in normal tension glaucoma and ocular hypertensive patients.

 
  References Top

1.
Grant WM, Burke JF Jr. Why do some people go blind from Glaucoma ? Ophthalmology 89:991-998, 1982.  Back to cited text no. 1
    
2.
Lundberg L, Wettrell K, Linner E. Ocular hypertension. A prospective twenty year follow up study. Acta Ophthalmol 65:705-70, 1987.  Back to cited text no. 2
    
3.
Armlay MF Lessions to be learnt from the collaborative glaucoma study. Surv Ophthalmol 25:139-144, 1980.  Back to cited text no. 3
    
4.
Sharir M, Zimmerman TJ. Initial treatment of glaucoma: surgery or medications. Medical therapy. Surv Ophthalmol 37:297-299, 1993.  Back to cited text no. 4
    
5.
Shultz JS. Initial treatment of glaucoma: surgery of medication Chop or drop. Surv Ophthalmol 37:293-299, 1993.  Back to cited text no. 5
    
6.
Wise JB and Witter SL. Argon laser therapy for open angle glaucoma. Arch Ophthalmol 97:319-322, 1979  Back to cited text no. 6
    
7.
Coakes R. Laser trabeculoplasty Br. J Ophthalmol 76:624-626, 1992.  Back to cited text no. 7
    
8.
Thomas JV, Simmons RJ, Belcher CD. Argon laser trabeculoplasty in the pre-surgical glaucoma patient. Ophthalmology 89:187-197,1982  Back to cited text no. 8
    
9.
The Glaucoma Laser Trial Research Group: The Glaucoma Laser Trial (GLT):2, Results of argon laser trabeculoplasty versus topical medications. Ophthalmology 97:1403-1413, 1990  Back to cited text no. 9
    
10.
Bergea B and Svedbergh B. Primary argon laser trabeculoplasty vs pilocarpine, short term results. Acta Ophthalmologica 70:454-460,1992.  Back to cited text no. 10
    
11.
Peto R, Pike MC, Armitage P et al. Design and analysis of randomised clinical trials requiring prolonged observations of each patient II. Analysis and examples. Br J Cancer 35:1-39, 1977.  Back to cited text no. 11
    
12.
Kaplan EL and Meier P: Nonparametric estimation from incomplete observations. J Am Stat Assoc 53:457-481, 1958.  Back to cited text no. 12
    
13.
Migdal C, Gregory W, Hitchings R. Long term functional outcome after earlyf surgery with laser and medicine in open-angle glaucoma. Ophthalmology 101:1651-1657, 1994.  Back to cited text no. 13
    
14.
Schwatz LW, Spaeth GL, Traverso C, Greenidge KC. Variation of techniques on the results of argon laser trabeculoplasty. Ophthalmology 90:781-784, 1983  Back to cited text no. 14
    
15.
Spaeth GL, Baez KA. Argon laser trabeculoplasty controls one third of cases of progressive, uncontrolled, open angle glaucoma for 5 years. Arch Ophthalmol 110:491-494, 1992  Back to cited text no. 15
    
16.
Glaucoma laser trial research group. The glaucoma laser trial 1. Acute effects of argon laser trabeculoplasty on intraocular pressure. Arch Ophthalmol 107:1135-1142, 1989.  Back to cited text no. 16
    
17.
Robin AL, Pollack IP, House B, Enger C. Effects of ALO 2145 on intraocular pressure following argon laser trabeculoplasty. Arch Ophthalmol 105:646-650, 1987.  Back to cited text no. 17
    


    Figures

  [Figure - 1], [Figure - 2]
 
 
    Tables

  [Table - 1], [Table - 2]



 

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