The Trabectome is a surgical device that can be used for ab interno trabeculotomy, a minimally invasive glaucoma surgery for the surgical management of adult, juvenile, and infantile glaucoma. The trabecular meshwork is a major site of resistance to aqueous humor outflow. As angle surgeries such as Trabectome follow the physiologic outflow pathway, the risk of complications is significantly lower than filtering surgeries. Hypotony with damage to the macula (hypotony maculopathy), can occur with pressures below 5 mmHg, for instance, after traditional trabeculectomy, because of the episcleral venous pressure limit. The Trabectome handpiece is inserted into the anterior chamber, its tip positioned into Schlemm's canal, and advanced to the left and to the right. Different from cautery, the tip generates plasma to molecularize the trabecular meshwork and remove it drag-free and with minimal thermal effect. Active irrigation of the trabectome surgery system helps to keep the anterior chamber formed during the procedure and precludes the need for ophthalmic viscoelastic devices. Viscoelastic devices tend to trap debris or gas bubbles and diminish visualization. The Trabectome decreases the intra-ocular pressure typically to a mid-teen range and reduces the patient's requirement to take glaucoma eye drops and glaucoma medications (see references). The theoretically lowest pressure that can be achieved is equal to 8 mmHg in the episcleral veins. This procedure is performed through a small incision and can be done on an outpatient basis.
Method When abdomino-interno trabeculectomy is combined with cataract surgery, it is initially performed for optimal angle visualization. Corneal clarity is often damaged during cataract surgery, and this damage may only be noticeable during gonioscopy, when the light path through the cornea is longer. An iris-lanar clear corneal incision of 1.8 mm width is made approximately 2 mm in front of the surgical limbus. Cataract surgery uses a larger keratome that requires the incision to be closed, to reduce fluid leakage. No viscoelastic is used, as it can cause bipolar electrodes to carbonize during the incision. The patient's head is then turned away from the surgeon by approximately 40 degrees, and the microscope is turned to the same extent in the opposite direction. Optimum gonioscopic trabecular meshwork visualization requires an angle of approximately 70 to 80 degrees between the microscope and the patient's eye. An incision is made, which is slightly gaping. This gaping encourages hypotony and enables easy identification of Schlemm's canal from refluxed blood. Trypan blue can also be used to stain the trabecular meshwork [18]. The trabectome handpiece is inserted, with irrigation turned on. If the anterior chamber is too shallow for it to be fully inserted, the irrigation ports in the metal sleeve can form the anterior chamber by resting against the outer edges of the incision, with the tip already inside the eye. Right-handed surgeons find it easiest to perform counterclockwise removal first. The trabectome is engaged in the trabecular meshwork. This is done with the tip angled 45 degrees upward, just in front of the scleral spur. This angle offers a pointed entry into the meshwork. The trabectome is then moved in a strictly parallel fashion, with no movement toward the wall of the canal. The handpiece is turned 180 degrees, completing the clockwise removal. The superior and inferior angle structures can be seen, and almost 180 degrees of meshwork are removed by tilting the goniolens toward the patient's brow and then toward their cheek. This can be done in reverse, depending on which eye is operated on. Once complete, the trabectome is carefully removed from the eye. Viscoelastic is injected into the eye for pressurization, and to tamponade the reflux heme. If cataract surgery is to follow, the microscope and patient's head are returned to their initial positions. The existing access point is used, and a larger keratome is employed to create a larger incision, with a self-sealing biplanar wound [2].
Training Microincisional glaucoma surgery [3, 4] is conducted in a space that is approximately 200 times smaller than the space used to implant epibulbar glaucoma drainage devices [5] As such, this type of surgery is particularly challenging to learn. The deep venous plexus distal to the outer wall of Schlemm's canal, the iris root, the ciliary body band and the suprachoroidal space all risk being damaged during surgery. This damage can cause variable sequelae [6, 7]. To master this surgery, it is important to be able to visualize the angle, identify the correct target, avoid trauma and maximize meshwork removal. Microincisional glaucoma surgery does not yet have dedicated simulators or synthetic models such as those used in cataract surgery wet labs. Therefore, most aspiring surgeons in this field practice on glaucoma patients. This is despite reported complications being almost ten times as common toward the end of training [8]. A safe and low-cost training environment has recently been created, using pig eyes mounted on a model head. This allows trainee surgeons to track their progress objectively. The pig eyes are infused with diluted fluorescein to trace outflow. Fluorescein can diffuse through the trabecular meshwork, which allows flow speeds to be estimated in non-treated parts of the eye. A disadvantage of this method is that over time, diffusion also takes place through intact vascular endothelium, staining the extravascular space. Fluorescent beads can be used as an alternative, and are suitable in less time-sensitive, more beginner-friendly studies of ablation. However, unlike fluorescein, this method does not account for flow speeds or volume estimates.
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