The Tube Versus Trabeculectomy Study supports the view that aqueous shunts can be a reasonable alternative in patients who have had prior eye surgery. Nonetheless, there are patients who would be better served by other surgical options. Following are some examples of conditions that might favor other glaucoma surgical options.
When Should Surgical Treatments Other Than Glaucoma Drainage Devices Be Considered?
Your “Target IOP” is around 10mmHg
If you have advanced or rapidly progressing glaucoma you may need a very low intraocular pressure (IOP) in order to slow the progression of your vision loss. An aqueous shunt may not be the best option in this case. Trabeculectomy with Mitomycin-C (MMC) is really the only glaucoma surgery that can be expected to achieve an IOP in the range of 10mmHg without the use of drops.
You have Normal or Low Tension Glaucoma (NTG or LTG)
In patients with Normal Tension Glaucoma (sometimes called low tension glaucoma) damage to the optic nerve occurs despite IOPs in the “normal” range. Because the intraocular pressure is already in the teens, those with NTG need IOPs in the low teens or even single digits (below 10mmHg). Realistically, as with anyone in need of such a low IOP, trabeculectomy with MMC is the only surgery that will achieve this target IOP without also using glaucoma drops.
You cannot tolerate any glaucoma medications and your target IOP is below 15mmHg
Glaucoma drainage devices can be expected to get the IOP into the high teens without additional use of glaucoma medications. Trabeculectomy with MMC, however, is really the only option for those patients who absolutely must have a very low IOP without the use of eye drops.
You have a low corneal endothelial cell count
Corneal endothelial cells have a critical job – keeping your cornea clear. If these cells are damaged then the cornea swells up and loses its transparency. Placement of glaucoma drainage devices are associated with endothelial cell loss. If you already have a low endothelial cell count (something that can be assessed with “specular microscopy” in the office) then a non-penetrating glaucoma surgery such as canaloplasty might be a better option for you.
1) Gedde SJ, Schiffman JC, Feuer WF, et al. Tube Versus Trabeculectomy Study Group. Treatement outcomes in the tube versus trabeculectomy study after one year of follow-up. Am J Ophthalmol. 2007;143:9-22.
2) Minckler DS, Francis BA, Hodapp EA, et al. Aqueous Shunts in Glaucoma. Ophthalmol. 2008;115(6):1089-1098.
3) Jacobi PC, Dietlein TS, Krieglstein GK. Adjunctive mitomycin C in primary trabeculectomy in young adults: a long-term study of case-matched young patients. Graefes Arch Clin Exp Ophthalmol 1998;236:652–7.
Rasheed el-S. Initial trabeculectomy with intraoperative mitomycin-C application in primary glaucomas. Ophthalmic Surg Lasers 1999;30:360–6.
Bindlish R, Condon GP, Schlosser JD, et al. Efficacy and safety of mitomycin-C in primary trabeculectomy: five-year follow-up. Ophthalmology. 2002;109(7):1336-1341; discussion 1341-1342.
4) McDermott ML, Swendris RP, Shin DH, et al. Corneal endothelial cell counts after Molteno implantation. Am J Ophthalmol. 1993;115(1):93-96.
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