The BOSs (….or the hostile takeover of the filtering bleb)

A few years back it was suggested that cystic blebs often failed due to development of scar (fibrous) tissue occurring posteriorly (Figure 1). 

Figure 1. The Ring of Steel in cystic blebs

This was called the “RING OF STEEL” (Figure 2).

Figure 2

However, what happens in flat blebs? These failing blebs do not show any significant bleb formation but start to develop a progressive increase in intraocular pressure (IOP), usually after a period of initial good IOP control.

Fibrous tissue overlying the bleb, causing failure

I did surgical revision of such failing blebs and found a band of tissue overlying the bleb area. This had effectively sealed the scleral flap, preventing aqueous from going out from under the flap. I have named this tissue, found in the subconjunctival area, as the “BAND OF STEEL” (BOS). This BOS is responsible for bleb failure in these cases.

As seen in the following figures, this tissue appears as a band and has to be completely excised in order to free the scleral flap. After excision of the BOS, I usually place Mitomycin-C 0.04% for about 3 minutes over the affected area. This is a higher concentration than the MMC 0.02% which I had been using previously. This higher concentration might be more conducive to prevent fibrosis and prevent formation of the “band of steel”.

BOS is being cut

The cut piece of BOS