MINIMALLY INVASIVE, GONIOSCOPICALLY ASSISTED REMOVAL OF PROLAPSED VITREOUS FROM TRABECULECTOMY SCLEROSTOMY

To describe a novel, minimally invasive technique of removing prolapsed vitreous from a trabeculectomy sclerostomy when this is recognised post-operatively. To compare widely available gonio lens systems for feasibility of use, and test whether the imaging inverter used for vitreoretinal surgery can help overcome mirror image difficulties associated with using a low-cost disposable indirect gonioscopy lens for angle surgery.

Surgical case and separate wet-lab model

A patient was found to have a raised intraocular pressure a week following uncomplicated combined trabeculectomy and phacoemulsification surgery. Vitreous was seen on clinic gonioscopy prolapsing from the iridectomy area into the sclerostomy sited in clear cornea.  As the trabeculectomy was not draining, the patient was taken back to theatre.

An initial attempt made to visualise the area with a Swan-Jacob direct gonio lens, with microscope- and head-tilting, was unsuccessful. The vitreous prolapse was hooked away from the sclerostomy with a viscoelastic cannula using the mirrored view of a disposable indirect gonioscopy lens. This manoeuvre has not previously been described, and is superior to simple anterior vitrectomy which risks leaving a cut segment of vitreous in the sclerostomy. A dry anterior vitrectomy supported with viscoelastic was performed within the iridectomy under indirect gonioscopy to eat away the freed vitreous wick.

A wet lab model was set up in an operating theatre using an indirect, single-mirror gonio lens and a dome-shaped mound of Healon GV viscoelastic on top of sterile glove wrapping with small-sized font text on it to simulate an anterior chamber, with the text aiding in identifying orientation. Image inversion on the microscope was tested to see if it could aid coordination of instruments within a gonio mirror image.

Even a superonasally placed sclerostomy could not be easily seen with a single-mirror direct gonio lens with axial tilting. A disposable indirect gonio lens offered a good view of the area without tilting, but surgical manipulations were mirrored and thus extremely challenging. Despite this, successful clearance of the sclerostomy with restoration of bleb function was achieved. Image inversion using a vitreoretinal microscope made the discrepancy between instrument and image movements worse by turning the whole field of view upside down.

Vitreous can be safely removed from a trabeculectomy sclerostomy gonioscopically to rescue function without an open revision. A direct single-mirror gonio lens is of no use. Using a single-mirror indirect gonio lens is technically difficult and not helped by an inverter. A double-mirror upright gonio lens would work, though these are less widely available.