Sir,
The results of the National Survey of Trabeculectomy II1 of ‘first time trabeculectomy’ for predominantly primary open angle glaucoma is seriously methodologically flawed, by failing to define success prior to undertaking the study. Rather, once data had been collected, the main success criterion was then defined as: intraocular pressure (IOP) at one year of less than two-thirds the preoperative IOP.
There is no evidence to suggest that reduction of IOP by one third stabilises visual fields in patients with primary open angle glaucoma.
There is ample evidence to suggest an upper limit of IOP of <15 mmHg will minimise further field loss.2,3 In order to prevent hypotony and its attendant complications, it is preferable to keep the IOP to >6.5 mmHg.4
Re-evaluating the study data using these values (ie, success means IOP between 6.5–15 mmHg), then ‘unqualified’1 (no additional ocular hypotensive medication) and ‘qualified’1 (additional ocular hypotensive medication) success of trabeculectomy in this series was 44.5% and 46.4%, respectively.
These figures cast doubts on continued use of trabeculectomy in the UK, because, put bluntly, they show that trabeculectomy as currently practised, is unlikely to achieve an IOP compatible with field stabilisation.
The situation may be even worse with longer follow-up, as Chen and associates in their study of patients with successful control of the IOP at one year, found control of the IOP reduced with time, with a failure rate of 3% per year.5
We would ask the authors of this study to formally respond, either accepting or refuting our analysis of the results. If our analysis is accepted, then individual ophthalmologists who perform trabeculectomy, need to re-assess their own position in relation to success and complication rates, particularly in terms of consent and use of adjunctive antimetabolites. Although antimetabolites improve the results of surgery in terms of IOP, they were used in only 6.4% of cases in this series.6,7
Also it cannot be acceptable that only 57.7% of the patients had visual fields performed during the year following surgery.1
References
Edmunds B, Thompson JR, Salmon JF et al. The National Survey of Trabeculectomy. II. Variations in operative technique and outcome. Eye 2001; 15: 441–448
Hitchings R . Primary surgery for open angle glaucoma. Br J Ophthalmol 1993; 77: 445–448
AGIS investigators. The AGIS study: 7. The relationship between control of intraocular pressure and visual field deterioration. Am J Ophthalmol 2000; 130: 429–440
Pederson JE . Ocular hypotony. In: Ritch R, Sheilds MB, Krupin T (eds). The Glaucomas, Vol I Mosby: St Louis 1996 385–395
Chen TC, Wilensky JT, Viana MAG . Long-term follow-up of initially successful trabeculectomy. Ophthalmology 1997; 104: 1120–1125
Rasheed ES . Initial trabeculectomy with intraoperative Mitomycin-C application in primary glaucomas. Ophthalmic Surg Lasers 1999; 30: 360–366
Yostron D, Khaw PT . A randomized trial of the effect of intraoperative 5-fluorouracil on the outcome of trabeculectomy in East Africa. Br J Ophthalmol 2001; 85: 1028–1030
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Murthy, S., Clearkin, L. The National Survey of trabeculectomy. II. Variations in the operative technique and outcome. Eye 16, 677–678 (2002). https://doi.org/10.1038/sj.eye.6700134
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DOI: https://doi.org/10.1038/sj.eye.6700134
