The role of early trabeculectomy in the control of chronic simple glaucoma.
Dept of Opthalmology, KEM Hospital, Parel, Bombay.
Y K Dastur
Dept of Opthalmology, KEM Hospital, Parel, Bombay.
Seventy patients of bilateral chronic simple glaucoma with a mean age of 59.7 years, an intra-ocular pressure over 25 mmg Hg, optic disc cupping, and without visual field loss were selected. The eye with higher intra-ocular pressure or the larger optic disc cup was treated by early trabeculectomy while the other eye of the same patient was subjected to medical therapy with topical beta blockers for 3 years (without any surgical treatment). Both the eyes of 70 patients were compared after 3 years. Eyes which had undergone trabeculectomy had a mean intra-ocular pressure of 11.7 mm Hg against 18 mm Hg in the medically treated eyes. Surgically treated eyes had decrease in the mean cup : disc ratio (from 0.54 : 1 to 0.48 : 1) whereas medically treated eyes showed an increase from 0.41:1 to 0.51: 1. Visual field loss occurred in 3/70 operated eyes and in 27/70 medically treated eyes. Twenty-one of 70 treated eyes developed cataract and 12 of these required cataract surgery. Only 18/70 medically treated eyes developed cataracts but none of these required cataract surgery. Early trabeculectomy in cases of chronic simple glaucoma resulted in a large reduction of intra-ocular pressure and consequently reduced the size of optic disc cup and the chances of visual field loss.
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Dastur Y K. The role of early trabeculectomy in the control of chronic simple glaucoma. J Postgrad Med 1994;40:74-7
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Dastur Y K. The role of early trabeculectomy in the control of chronic simple glaucoma. J Postgrad Med [serial online] 1994 [cited 2022 Dec 10 ];40:74-7
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Chronic simple glaucoma is a disease of insidious onset and progressive course, which terminates in blindness if not adequately treated. The usual practice of using anti-glaucoma medications such as topical miotics and beta blockers often result in a lowering of the intra ocular tension to the upper limit of normal. Hence, optic disc changes and visual loss continue to progress resulting in visual deterioration,,. There is presently a trend towards earlier trabeculectomy in cases of chronic simple glaucoma even before maximum therapy has failed. Surgical therapy produces a greater reduction in intra-ocular tension than medical therapy.
In spite of reduction of intra-ocular tension by trabeculectomy, visual field loss continues to occur in some cases. Recently by using anti-fibrosis regimen with trabecuiectomy, intraocular tension can be further lowered to a level, which can effectively stop any further progression of glaucoma and yet allow for any possible improvement in function. Patients with very low intra-ocular tension after trabeculectomy and anti-fibrosis regimen often have fluctuating and seriously blurred vision.
This study is being conducted with a view to evaluate the efficacy of early trabeculectomy without anti-fibrosis regimen in early cases of chronic simple glaucoma. The study also aims to determine whether a greater reduction in intra-ocular pressure achieved by trabeculectomy has a protective effect against the visual field loss and optic disc. changes of chronic simple glaucoma.
A prospective study was conducted in 70 patients (age range 42- 74 yrs, mean: 59.7 yrs; M: F = 4:3) [Table:1] of early chronic simple glaucoma having bilateral sigh.
Hence, 140 eyes were evaluated. Exclusion criteria were patients with either unilateral chronic simple glaucoma, or bilateral chronic simple glaucoma with advanced visual field changes, those with low tension glaucoma, those who had undergone prior topical therapy for glaucoma where, and patient with associated tension or diabetes.
The patients selected for the study had intraocular pressure above 25 mmg Hg on applanation tonometry, glaucomatous cupping with cup disc ratio of 0.3 : 1 or more as judged by opthalmoscopy and absence of visual field loss on kinetic perimetry. Slit lamp examination and gonioscopy were done to rule out secondary and narrow angle glaucoma respectively.
Of the two eyes affected, one with the higher intra-ocular tension or with the larger cup disc ratio was selected for early trabeculectomy. The surgery was carried out after controlling intra-ocular pressure with either use of 0.25% or 0.5% timolol or 0.5% or 1% betaxolol eye drops. The operation was done under local anaesthesia Watson's modification of trabeculectomy consisting of a limbal based conjunctival and lamellar scleral flap was performed. The opposite eye of the same patient was selected for medical therapy. Either 0.25% or 0.5% timolol eye drops were used twice daily for three years after ascertaining whether the patient had any previous history of pulmonary disease or bronchial asthma. The patients with pulmonary disorders were treated with 0.5% or 1% betaxolol eye drops twice daily for 3 years. Topical pilocarpine and oral acetazolamide were not used in any patients of this study.
Post-operative hospitalisation was for 3 days. The patients received oral antibiotics along with topical steroids and antibiotics. They were examined at weekly intervals for the first four weeks and subsequently intra-ocular pressure and fundus examination was done at monthly intervals for 3 years. Visual field was checked every 6 months by kinetic perimetry during the three year study period.
The patients who did not attend the above follow ups or used topical therapy irregularly were considered as drop-out and were not included in analysis.
The patients who developed advanced cataract was operated by the extra-capsular technique with posterior chamber implant through an upper quadrant clear comeal incision.
Pre-treatment intra-ocular pressure in 37170 eyes (53%) treated surgically was in the range of 30 - 40 mmg Hg. In contrast, 45/70 eyes (64%) treated medically had pressure in the range of 20-30 mmg Hg [Table:2]. The mean pre-treatment intra-ocular pressure of former group was 34.5 mmg Hg and of medically treated group was 28.8 mmg Hg. 40/70 eyes (57%) with cup disc ratio greater than 0.5: 1 were treated surgically. Thirty-six of seventy eyes which received medical therapy had cup disc ratio of 0.3 : 1 [Table:2]
The mean cup disc ratio of surgically treated eyes was 0.54 : 1 and of medically treated was 0.4 :1.
At 3 years of follow up. 47170 eyes (67%) operated for trabeculectomy had intra-ocular pressure in the range of 10-20 mmg Hq with a mean intraocular pressure of 11.7 mmg Hg. The mean cup disc ratio was found to be 0.48:1 with 37% eyes having range between 0.3 - 0.5: 1.
41/70 eyes (58%) treated medically for chronic simple glaucoma were found to have intracicular pressure in the range of 10-20 mmg Hg with a mean of 18 mm Hg at 3 years follow-up. At the same time 32/70 eyes (45%) showed cup disc ratio of more than 0.51 with a mean of 0.51 : 1 [Table:2].
None of the patients had any visual field defect at the time of inclusion. After 3 years. 3 eyes (4.3%) from surgically treated group and 27(39%) from medically treated group showed evidence of visual field loss on kinetic perimetry.
At presentation 51/70 eyes (73%) from surgically were operated by the extra-capsular technique with treated group had 6/12 or better vision. After trabecuiectomy at 3 years follow up only 35/70 eyes (50%) had 6/12 or better vision [Table:3].
The principal cause of diminished vision after trabeculectomy was cataract, which progressed in 21/70 eyes (30%) Twelve of the 21 cataracts were subsequently operated by extraction and posterior chamber implant. These showed 6112 or better visual recovery. None of these 12 eyes had any operative complication.
In contrast, 64/70 eyes (91%) treated with drugs for chronic simple glaucoma had 6/12 or better vision at presentation. After medical therapy, 49170 eyes (70%) had better than 6/12 vision at 3 years follow-up [Table:3], Even with medical therapy, cataract development was observed in 18/70 eyes (25%), though none of them needed operative treatment during the 3 year follow-up.
This study shows that 70 eyes operated for trabeculectomy had a 60% reduction of intra-ocular pressure (from a mean pre-treatment value of 34.5 mm Hg to 11.7 mmg Hg) at 3 years follow-up. Jay and Murray, Kidd and O'Connor and Lavin, et al have reported values of mean intra-ocular pressure following trabeculectomy as 15 mmg Hg, 15 mmg Hg, 13 mm H9 respectively. Kidd and 0' Connor have found 40% reduction of mean intra-ocular pressure after 5 years of trabeulectomy. In our study, 70 eyes treated medically for 3 years had a 30% reduction of intra-ocular pressure from a mean value of 28.8 mm Hg to 18 mm Hg. Jay and Murrays and Lavin et al have reported post-medical treatment mean intra-ocular pressure of 21 mm Hg and 18 mm Hg respectively.
The mean cup disc ratio of the 70 eyes treated with trabeculectomy decreased from 0.54 : 1 to 0.48:1 and of medically treated eyes increased from 0.41:1 to 0.51: 1. This means that the 30% reduction of intra-ocular pressure achieved with medical therapy did not stop progressive increase in the size of the glaucomatous cup. However, the 60% reduction of intra-ocular pressure seen after trabeculectomy did reduce the size of the glaucomatous cup. Katz, et al had detected decrease in cupping when the intra-ocular pressure was reduced by 30% or more.
70 eyes treated by trabeculectomy, after a 3 year follow-up, showed visual field loss in 3/70 eyes (4.3%). However, same number treated medically showed field loss in 27/70 eyes (39%). This confirms the fact that surgery, which produces a lower mean intraocular pressure than with medical therapy, has a protective effect against progressive visual field loss,,,,.
At the time of presentation 51/70 eyes (73%) in our study had 6/12 or better visual acuity but after 3 years of trabeculectomy 35/70 eyes (50%) had 6/12 or better vision. The Main cause was found to be cataract in 21/70 eyes (30%). Other workers have also reported incidence of 10% and 30% after trabeculectomy.
Following medical therapy, only 70% eyes (49/30) showed visual acuity of 6/12 or better instead of initial 91% (64/70) eyes. Cataract was detected in 18/70 of these eyes but none required operative therapy.
This study shows that early trabeculectomy in cases of chronic simple glaucoma results in a lower intraocular pressure than with medical therapy; further the greater reduction of intra-ocular pressure helps to reduce the size of optic disc cup and lowers the possibility of visual field loss. It does cause a greater degree of cataract progression but after the extracapsular technique and posterior chamber implant visual recovery is usually possible.
Visual field loss once occurring in chronic simple glaucoma progresses very rapidly,. Hence trabeculectomy should be done early before visual field loss supervenes.
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