Ring of Steel Formation Following Trabeculectomy with Mitomycin-C
Dr Swati Mishra, Dr Prabhat Nangia, Dr Sarang Lambat, Dr Vinay Nangia
A female, 66 years of age, reported to SEI with complaints of pain redness and photophobia since 1 day. She had a visual acuity of 6/6p in right eye (RE) and 6/6 in left eye (LE). Anterior segment examination showed early cataract in both eyes. Intra Ocular Pressure (IOP) was 12 mmHg in the right eye and 18 mmHg in left eye. Gonioscopy showed occludable but open angles in both eyes. Central corneal thickness was 520 microns in RE and 513 microns in LE. Fundus examination showed 0.8 vertical cup disc ratio (VCDR) and inferior rim thinning in RE and 0.9 VCDR in LE. SDOCT showed RNFL thinning in infero temporal and infero-nasal sector in RE and nasal, naso inferior, temporo inferior and temporal in LE. She was advised trabeculectomy with mitomycin C in both eyes- LE followed by RE. One week following LE trabeculectomy the IOP was 2 mmHg with shallow thin functional bleb in left eye. After 1 month, IOP was 12 mmHg in left eye with a diffuse thin walled pale bleb. After 3 months, ring of steel formation around the bleb was noted with an IOP of 34 mmHg in left eye. She was put on anti glaucoma therapy (Brimonidine + Timolol) and further surgical management is being considered.
“Ring of steel” refers to a peri-bleb ring of scar tissue seen commonly in limbal based conjunctival flap. Dr. Khaw et. al. observed that cystic blebs have 2 things in common: (1) anterior aqueous drainage, and (2) a peri-bleb ring of scar tissue known as “ring of steel”.
When the conjunctival incision is not posterior enough, limbal based conjunctival flap are more likely to result in a cystic bleb. With a fornix based conjunctival flap it is easier to achieve a larger area of MMC treatment, which prevents the ring of steel. Additionally, incompletely cut sides of a large scleral flap leads to posteriorly directed, diffuse flow of aqueous resulting in formation of a more diffuse, non cystic bleb. Thus, the ring of steel may be prevented by fornix based flap, broader application of anti metabolites and incomplete side cuts of scleral flap, not reaching up to the limbus. Prevention of ring of steel formation is important for IOP control post trabeculectomy with MMC.
In our patient we did a fornix based flap. While all guidelines are generally followed, it may be important to consider the following. There should be sufficient posterior dissection, and posterior placement of the mitomycin- C soaked sponge elements over a relatively wide area. The development of ring of steel may however also depend on the conjunctiva-tenons complex and how it responds to the mitomycin-C and the relative survival of the vasculature and its ability to respond aggressively to the MMC affected area, which the healthy ocular tissues would consider as toxic avascular tissue. The vasculature tends to grow towards the area of conjunctiva which is most affected by the mitomycin to become unhealthy and pale. Decrease in size of bleb therefore is a part of the growth of the vasculature towards the mitomycin-c affected bleb and the tendency of the ring of fibrosis to contract in a centripetal manner. There are many instances, where there is formation of the ring of steel, but the bleb stays functional and does not contract at least initially. Whereas in some cases the growth of the vessels is so aggressive that the contraction of the bleb continues. A static ring of steel of sufficient size, may be associated with better IOP control. What is important is to identify patients through more frequent follow up, where the centripetal contraction is taking place associated with an increase in IOP. This process generally indicates impending failure of IOP control.
- Khaw PT, Jones E, Mireskandari K, et al. Modulating wound healing after glaucoma surgery. Curr Opin Ophthalmol.2001 April. 2004;doi. 10.1097/00055735-200104000-00011
- Enhanced Trabeculectomy – The Moorfields Safer Surgery System Bettin P, Khaw PT (eds): Glaucoma Surgery. Dev Ophthalmol. Basel, Karger, 2012, vol 50, pp 1–28. doi: 10.1159/000458483
- Kurado et al. Fornix- based versus limbal-based conjunctival flaps in Trabeculectomy with mitomycin C in high risk patients, Clin Ophthalmol May2014 doi: 10.2147/OPTH.S61342
Dr Vinay Nangia
MS, FRCS, FRCOphth
Department of ophthalmology
Suraj Eye Institute