Case Description
A 64-year-old female had a prior subconjunctival stent which had failed, with tenons fibrosis. The contralateral eye had counting fingers vision after hypotony from tube shunt. The failed subconjunctival stent had previously been performed with a conjunctival dissection from an external approach.
The patient declined further intervention including diode CPC when her subconjunctival stent failed. She was only amenable to revision.
Pre-operative assessment
Pressure was very elevated pre-operatively, with an IOP of 31mmHg in the right eye. To lower the risk of subconjunctival hemorrhage, the patient was started on oral acetazolamide. The surgeon also proceeded to bleb revision within a week after pre-treating with difluprednate.
The surgical plan was to revise the old subconjunctival stent and place a new one if there was no flow, using the intraoperative OCT on the wound closure to determine if the implant was free of Tenon's tissue.
Surgical approach
After the peritomy, subconjunctival marking was injected, working with great care around the scar tissue to avoid cutting or damaging the stent in case it could be left in. However, there was a wall of Tenon's tissue around it (Figure 1).
With a 27-gauge needle, it was freed from the surrounding tissue. There was not a lot of ischemia from the prior mitomycin treatment often associated with these stents, but there was no flow through the device.
Despite attempting to back-flush the device and blow through any clog in the stent through a firm injection, there still was no flow (Figure 2). As such, the decision was made to remove the stent to avoid two filtration procedures. The stent was removed very carefully given its fragility and brittleness.
Before placing a new stent, a pocket was dissected. An external approach was taken, using a modification of a non-FDA approved technique. The device was placed into the anterior chamber with the injector (Figure 3). Wing sutures were used to close, with a final mattress suture to obtain a tight area of conjunctiva across the limbus (Figure 4).
Intraoperative OCT was used to confirm the stent was free, with no Tenon's tissue below it (Figure 5).
Post-operative outcomes
After surgery, the patient received mitomycin. The month 12 followup showed good eye pressure at goal, at IOP 16mmHg on dorzolamide and timolol. In addition, the last visual field test has not shown progression.
Conclusions
Intraoperative OCT provides vital information for subconjunctival stent surgery. It allows to see clearly whether the stent is embedded in the Tenon's layer. Dr. Sheybani has observed that, when the Tenon's tissue is needled or swept away after placing the stent, the functionality of the device is improved.
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