Angle stability and outflow in dual blade ab interno trabeculectomy with active versus passive chamber management

Abstract

Purpose: To compare intraoperative angle stability and postoperative outflow of two ab interno trabeculectomy devices that excise the trabecular meshwork with or without active aspiration and irrigation. We hypothesized that anterior segment optical coherence tomography (AS-OCT) allows for a quantitative comparison of intraoperative angle stability in a microincisional glaucoma surgery (MIGS) pig eye training model.

Methods: Twelve freshly enucleated porcine eyes were measured with AS-OCT at baseline, at the beginning of the procedure and at its conclusion to determine the anterior chamber depth (ACD) and the nasal angle α in degrees. The right and left eye of pairs were randomly assigned to an active dual blade goniectome (aDBG) and a passive dual blade goniectome (pDBG) group, respectively. The aDBG had irrigation and aspiration ports while the pDBG required surgery under viscoelastic. We performed the procedures using our MIGS training system with a standard, motorized ophthalmic operating microscope. We estimated outflow by obtaining canalograms with fluorescent spheres.

Results: In aDBG, the nasal angle remained wide open during the procedure at above 90° and did not change towards the end (100±10%, p = 0.9). In contrast, in pDBG, ACD decreased by 51±19% to 21% below baseline (p<0.01) while the angle progressively narrowed by 40±12% (p<0.001). Canalograms showed a similar extent of access to the outflow tract with the aDBG and the pDBG (p = 0.513). The average increase for the aDBG in the superonasal and inferonasal quadrants was between 27 to 31% and for the pDBG between 15 to 18%.

Conclusion: AS-OCT demonstrated that active irrigation and aspiration improved anterior chamber maintenance and ease of handling with the aDBG in this MIGS training model. The immediate postoperative outflow was equally good with both devices.

Fig 1. Active and passive dual blade goniectome.

The active dual blade goniectome (active DBG, left [7,8]) has two irrigation ports that maintain the chamber (blue arrows). The trabecular meshwork is put under stretch by an angle shaped ramp and excised by a left and a right blade. The cut trabecular meshwork strip, blood and debris are aspirated into the tip (red arrow). The passive dual blade goniectome (passive DBG, right [6]) requires viscoelastic to maintain the anterior chamber. It also puts the trabecular meshwork under stretch by an angle shaped ramp and cuts the trabecular meshwork with a left and a right blade. The trabecular meshwork strip can be left in the eye or amputated and extracted with microforceps.

Fig 2. Intraoperative view of active and passive DBG.

The active DBG (top) with an active irrigation and aspiration system. The anterior chamber was stable in both the left and the right pass. A supraphysiological deepening put the trabecular meshwork on tension and in direct view. Debris was aspirated. The passive DBG (bottom) required a viscoelastic to maintain the space. Air bubbles that were trapped in the viscoelastic (left asterisk) could not be removed without retracting the instrument from the eye. The anterior chamber became progressively more shallow as viscoelastic was displaced resulting in a narrowing angle and view obstruction from a billowing iris (right asterisk). Corneal striae from relative hypotony can be seen as well (right asterisk).

Fig 3. Intraoperative anterior segment optical coherence tomography (AS-OCT).

Behavior and stability of the anterior chamber depth (ACD, green bar in A) and nasal angle opening (α, green dotted lines, A) was measured with AS-OCT. The irrigation and aspiration of the active dual blade goniectome maintains the space during surgery allowing unhindered view of the chamber angle (active DBG, B and C). The passive DBG utilizes a viscoelastic resulting in a progressively narrowing chamber angle (passive DBG, E and F). The anterior chamber depth decreased by 51±19% (p<0.01*) during passive DBG while it remained unchanged during active DBG (106±7%, p = 0.5). The anterior chamber angle decreased by 40±12% (p<0.001*) during passive DBG but it remained unchanged during active DBG (100±10%, p = 0.9).

Fig 4. Outflow enhancement in aDBG and pDBG eyes.

All quadrants experienced a significant increase of fluorescence (SN = superonasal, IN = inferonasal, IT = inferotemporal, ST = superotemporal quadrant). In average, there was more outflow enhancement in active dual blade gonioectome (aDBG) than in passive DBG eyes, but there was no statistically significant difference between six aDBG and six pDBG eyes examined here (p>0.05).