Fig. 2.1
Two malpositioned iStent implants
Superficial Implantation
If the iStent is too superficial or incompletely inserted, there is a risk of detachment. In the case of superficial implantation, the iStent does not penetrate the trabecular meshwork completely and can be just engaged in the superficial layers of the trabecular meshwork. In this case there would be no communication between the anterior chamber and the Schlemm’s canal so the implant would not be efficacious. Moreover, it could come loose over time. Repositioning should be considered, but as mentioned before, most of the time the implant will settle on the iris root and cause no problems.
Cyclodialysis Cleft/Suprachoroidal Implantation
If IOP is very low during the first week a cyclodialysis cleft has to be ruled out. Also if the iStent is not seen in the angle and the iris root/ciliary tissue appear to have been damaged the area should be imaged with OCT or UBM to find the stent. Most of the cases can be managed conservatively as the cleft will close over time. If pressure remains too low or maculopathy develops, it may be necessary to suture the cleft. If the iStent is in the suprachoidal space but there is no inflammation removal is not necessary but close follow-up is required.
Late Postoperative Complications
A 5-year case series study by Arriola et al. showed no major complications regarding stent placement in the meshwork in a 19 patient study after 5 years (Arriola-Villalobos et al. 2012).
IStent obstruction
If the Stent is rotated toward the iris, the anterior chamber is narrow and not very deep or the iris is floppy, the aqueous humor flow to the iStent could facilitate the blockage of the device with the iris. This situation can be resolved by lasering the iris in order to unblock the stent snorkel. This has been described for both implant types (Fernandez-Barrientos et al. 2010; Arriola-Villalobos et al. 2012; Arriola-Villalobos et al. 2013; Fea 2010; Samuelson et al. 2011).
Endothelial damage
Arriola-Villalobos et al. (2013) analyzed prospectively the endothelial changes after combined surgery (Phaco + GTS400/Glaukos inject). At 2 years of follow-up the endothelial cell count decrease was 13.22 %, a reduction similar to that reported after phacoemulsification alone. However, if the implant was malpositioned and in contact with the corneal endothelium, it should be removed to avoid progressive endothelial damage.
2.2.2 Hydrus
2.2.2.1 Safety and Efficacy
The Hydrus Microstent (Ivantis, Irvine, USA) has been evaluated in an industry-funded randomized controlled trial in which 100 patients with open-angle glaucoma and cataract were randomized to receive either Hydrus implantation with concomitant phacoemulsification or phacoemulsification alone (Pfeiffer et al. 2015). Washed-out diurnal IOP was evaluated at baseline, 12 months and 24 months. IOP-lowering medications were allowed at other times if follow-up IOP exceeded 19 mmHg or there was evidence of progressive optic nerve damage or visual field loss. Mean diurnal IOP was calculated from measurements made using a two-person system (observer and reader), with at least two readings being made at each of three time points, spaced 4 h apart between 8 am and 4 pm.
At 24 months, the proportion of patients with 20 % reduction in washed-out diurnal IOP was 80 % in the treatment group compared to 46 % in the control group (p = 0.0008) assessed on an intention-to-treat basis. In a separate analysis that excluded patients who did not wash out medications for safety reasons, a 20 % reduction in washed-out diurnal IOP was achieved in 89 % of the treatment group versus 64 % of the control group (p = 0.0140). Washed-out mean diurnal IOP at 12 months was 16.6 mmHg in the treatment group versus 17.4 mmHg in the control group. At 24 months, washed-out mean diurnal IOP was 16.9 mmHg in the treatment group compared to 19.2 mmHg in the control group (p = 0.0093). The proportion of patients using no hypotensive medication at 24 months was 73 % in the treatment group compared to 38 % in the control group (p = 0.0008).
In terms of adverse events, peripheral anterior synechiae formation was noted in 19 % of treated patients versus 2 % of controls at 24 months (p = 0.0077). However, the presence of PAS was not thought to affect IOP or medication outcomes. Best-corrected visual acuity decreased by 2 lines in 2 patients in the treatment group, but resolved by 1 month. By month 3, best-corrected visual acuity was 20/40 or better in 96 % of subjects in the treatment group versus 90 % in the control group. Hypotony and stent migration were not found in the treatment group. Secondary glaucoma surgery was required in 2 % of the treatment group versus 4 % of the control group, and the difference was not statistically significant.
2.2.2.2 Patient Selection and Procedure
The Hydrus implant is an 8 mm crescent-shaped implantable device. The implant is very flexible, made from nitinol (a nickel/titanium alloy), and is preloaded onto a handheld delivery system. The device not only bypasses the trabecular meshwork but scaffolds and dilates the Schlemm’s canal. Due to its flexibility it easily sits in the Schlemm’s canal and dilates it. As it scaffolds around one quarter of the canal it can provide access to multiple aqueous channels.
The surgery set-up is similar to the IStent surgical procedure described above, and a goniolens is needed to visualize the angle. Surgery can be performed under topical anesthesia or the technique of choice of the surgeon. Acetylcholine can be used in combined procedures; it can be implanted through the same corneal incision used for the phacoemulsification. For Hydrus alone procedures the implant can be inserted through a 1–1.5 mm corneal incision. If the target implantation site is not easily accessible/visible through the phaco incision, a secondary incision can be performed opposite to the desired implantation site.
After filling the anterior chamber with viscoelastic the delivery system is introduced in the anterior chamber and advanced until the inserter tip comes into contact with the trabecular meshwork. The trabecular meshwork is perforated using the beveled tip of the cannula. Once opened the device is implanted into the Schlemm’s canal by rotating the advancement mechanism with one finger. The inserter terminal segment should be positioned parallel to the canal (flat angle) and with the bevel pointing slightly up. Otherwise, during the delivery the device could move down and out of the canal. Also if the angle between the angular surface and the inserter is excessive or the position is forced there could be problems with the delivery. The implant should advance with little or no resistance, if resistance is found the implant can be retracted and the position can be cautiously modified.
Once the implant is in place, the central core wire of the delivery system is retracted, allowing the complete detachment of the implant. The inlet segment (1–2 mm) should remain in the anterior chamber and the rest of the implant in the canal. On confirmation of the implant position, surgery is completed once the viscoelastic has been removed.
Conceptually the indications of the Hydrus implant are similar to the iStent. But, due to the dual action of the Hydrus implant, which bypasses the trabecular meshwork and expands the Schlemm’s canal thus giving access to multiple collector channels, it is possible that the IOP reduction could be higher than after iStent implantation. However, this higher efficacy has still to be established.
2.2.2.3 Complications
Reported complication rate is very low, and when performed in combination with phacoemulsification the rate is similar to a cataract alone procedure (Pfeiffer et al. 2015).
Intraoperative Complications
To avoid intraoperative complications it is very important to visualize the tip of the inserter, be careful when crossing the pupil with the inserter in phakic eyes and avoid any movement during the “injection” of the Hydrus into the Schlemm’s canal. The inserter has to be held steady and kept in contact with the angular tissue with the bevel slightly up. Also, note that the rotation knob of the inserter can be adjusted so the position of the bevel is comfortable for the surgeon.
Bleeding
When the procedure is performed correctly some bleeding is very common and also indicates the reflux of blood from the venous system. This bleeding will not affect the patient’s recovery or the final outcome. The presence of blood in the Schlemm’s canal can also help to detect the best areas for implantation. If when touching the trabecular meshwork the blood prevents the correct visualization of the tip or the progression of the device it may be necessary to retrieve the implant, wash out the blood and viscoelastic, wait for the bleeding to stop, and then proceed again with the implantation. If the device touches/ruptures the iris or is implanted in the ciliary body, the bleeding could be more severe and may take some time to stop. If visualization is not good and the surgeon is unsure of a possible damage to the iris or ciliary body, cancelling the procedure should be considered and then wait for the eye to recover.
Incomplete/incorrect insertion
The implant should be inserted so that only the inlet is outside the canal. The insertion angle is extremely important and after opening the meshwork the bevel should be angled up so that the device finds its way into the Schlemm’s canal. If the bevel is positioned to facilitate a “direct” insertion into the Schlemm’s canal (parallel to iris root) this may result in the implant going downwards damaging the angular structures or even the ciliary body and the iris.
Occasionally if resistance is found and the implant does not progress smoothly during implantation, the device should not be released. Sometimes if the device is stuck, movement is transferred to the inserter, moving it in the opposite direction to the injection movement thus exposing the implant that should remain in the same position, as it is not being introduced further in the Schlemm’s canal. It is very important to recognize this situation and retract the device into the inserter again. The first step is to check the insertion angle and if after a second attempt, the device is stuck in the same place a good option is to move to another area even if a new incision is needed. In any case, the implant should not be released until the surgeon is sure that it is correctly and completely implanted in the canal. Although the device can be pushed into the Schlemm’s or pulled out with a manipulator or a blunt instrument, these maneuvers are only effective when correcting a minor positioning problem. If any of the windows of the implant are even partially seen in the anterior chamber, removal of the device should be considered. If trabecular damage is not significant, the surgeon can consider implanting a second one. Depending on the damaged area it may be necessary to target or find another implantation site (Fig. 2.2).
Fig. 2.2
Incomplete/incorrect placement of Hydrus implant, with most of the implant in the anterior chamber
Adequate position of the implant should be checked after implantation. As some bleeding is very common sometimes it might be necessary to remove the viscoelastic and the blood. Although not always possible, it is recommended to check the whole implant from the distal end to inlet.
Tearing of the trabecular meshwork
If the grip is not firm enough or there are movements during the insertion, the device may rupture the trabecular meshwork exposing the external wall of the Schlemm’s canal. If there is not much bleeding a second implantation attempt can be performed.
Supraciliary/suprachoroidal implantation
As in the case of the iStent, if the angle structures are not correctly identified there is an increased risk of damaging the ocular structures. The implantation of a device like this in the ciliary body is painful and involves a high risk of severe bleeding. It is important to recognize this situation as soon as the implant starts to dissect the ciliary body tissue and retract the device into the inserter. If the implant was completely released it should be removed using retina forceps. Depending on the ocular situation and the possible damage to the ciliary body and iris a new device could be implanted.
Iris or lens damage Rupture of the iris
During the surgical procedure the surgeon should visualize the tip of the inserter and be careful to avoid touching the lens (in phakic eyes), cornea or the iris. Extra movements or surgical maneuvers increase the risk of damaging the ocular structures. If these maneuvers are needed for any reason, correct visualization is key to prevent further damage. If the device has to be removed, it is important to proceed slowly and control both ends of the device, also forceps should be used with care to avoid capturing the iris. If visualization of the device and/or angular structures is not good enough (blood or mixture of viscoelastic and blood), it can be improved by waiting for the bleeding to stop and then washing out the blood and viscoelastic.
Early Postoperative Complications
Hyphema
Some bleeding is common and is not usually a problem. Pfeiffer et al. did not report any severe complications related to bleeding.
Malposition
If for any reason, the position of the device could not be checked intraoperatively it should be as soon as possible. If the device is dislocated, or partially out of the Schlemm’s canal it is probably better to remove it. Depending on the ocular conditions and IOP a new device can be implanted in the same surgery.
Late Postoperative Complications
There is little published evidence on the long-term complications; however, this device seems to be very safe.
Corneal Endothelial Cell damage
If the surgery is uneventful and the device position correct, the possibility of significant endothelial damage is very low.
Peripheral Anterior Synechiae (PAS) and Inlet Obstruction
Pfeiffer et al. reported that 18.8 % of patients may develop anterior synechiae after 2 years. These PAS were located at or near the inlet segment of the implant and consisted in focal iris tissue adhesion to the device or chamber angle usually of less than 1 clock hour. However, PAS did not have a negative impact on the success rate. In this series, no cases of complete blockage of the inlet by the iris were found.
2.2.3 Trabectome
The Trabectome (NeoMedix, Tustin, USA) is designed to electrosurgically ablate the trabecular meshwork and inner wall of Schlemm’s canal. This enables aqueous to bypass the juxtacanalicular trabecular meshwork and inner wall of Schlemm’s canal, which is thought to be the main site of resistance in open-angle glaucoma (Overby et al. 2009).
2.2.3.1 Safety and Efficacy
Results from the use of the Trabectome were first reported by Minckler et al. (2005). Company data for 4659 treatments show that it safely reduces the need for drops for several years and reduces IOP by 26 % (Mosaed 2014). A retrospective study suggested that Trabectome is less effective than trabeculectomy (Jea et al. 2012a). To date, there are no published randomized controlled trial data.
Rates of successful IOP control decline with time, particularly in the first year postoperatively (Ahuja et al. 2013; Minckler et al. 2008; Mosaed 2014). Success rates reported in case series vary from 64 % to over 80 % at 12 months postoperatively, and from 62 % to more than 75 % at 24 months. Interpretation of results is hampered by the absence of clear criteria for the use of IOP-lowering medications in the postoperative period and by loss to follow-up of a significant proportion of patients.
Trabectome treatment may be more effective when combined with cataract surgery (Ahuja et al. 2013; Francis 2010; Jordan et al. 2013). Phacoemulsification itself has been shown to lower IOP (Chen et al. 2015; Mansberger et al. 2012), and the relative contributions of Trabectome and phacoemulsification are not yet defined by randomized trials.
Recently, it has been reported that Trabectome treatment may be effective in relatively narrow angles (Bussel et al. 2015a) and also in patients after failed trabeculectomy (Bussel et al. 2015b). Trabectome does not violate the integrity of the conjunctiva, and one cohort study suggests that the success of subsequent trabeculectomy is not compromised (Jea et al. 2012b).
In a single-center case series (Ahuja et al. 2013), the commonest complications were hyphema (46 %), microhyphema (27 %), and IOP spike (22 %). Other complications that have been reported include reduction in visual acuity >2 lines (0–5 %) (Ahuja et al. 2013; Minckler et al. 2008), delayed onset hyphema (5 %) (Ahuja et al. 2012), and aqueous misdirection (0.4 %) (Ahuja et al. 2013). In the manufacturer’s case series (Mosaed 2014), hypotony (IOP < 5 mmHg) at day 1 occurred in 1 % but sustained hypotony at 1 month was rare (0.2 %). Secondary surgery was required in 7 % of cases.
2.2.3.2 Patient Selection and Procedure
Trabectome surgery may be performed under local anesthesia. The Trabectome probe consists of an irrigating-aspirating handpiece which is introduced into the anterior chamber through a 1.6 mm temporal incision in clear cornea. Under gonioscopic guidance, the end of the probe is advanced across the anterior chamber towards the nasal trabecular meshwork. The footplate of the probe is inserted through the trabecular meshwork into the lumen of the nasal part of Schlemm’s canal. The footplate is then advanced along the lumen of Schlemm’s canal while electrosurgical power is applied to ablate the inner wall of Schlemm’s canal and the overlying trabecular meshwork.
Phacoemulsification can be performed after the Trabectome surgery through the same corneal incision, following enlargement, or via a separately placed incision. Some surgeons argue that phacoemulsification should be performed prior to Trabectome surgery, not afterwards. This way, the surgical view is less likely to be compromised by blood reflux following Trabectome surgery and the drainage angle may be more open and accessible. On the other hand, any reduction in corneal clarity at the end of phacoemulsification is likely to produce a poor gonioscopic view for Trabectome surgery.
Patients need to have surgically visible and accessible nasal drainage angles. To permit a gonioscopic view of the drainage angle, the patient must be able to rotate his or her head away from the surgeon. Inability to do this is a contraindication for surgery. Similarly, corneal opacities are a relative contraindication to surgery. Angles that appear to be relatively narrow on gonioscopy in the clinic may nonetheless be accessible surgically because the pressure of irrigation from the handpiece causes the lens-iris diaphragm to move posteriorly. However, angles that have peripheral anterior synechiae are unlikely to be amenable to treatment, because the iris tissue may not ablate easily and is liable to bleed heavily. The pupil is usually dilated if combined Trabectome-phacoemulsification is planned. Otherwise, preoperative application of pilocarpine eye drops may assist with opening the drainage angle. Through miosis, folds of iris are moved away from the ablation site and the crystalline lens is relatively protected from trauma. If, despite these precautions, iris is being aspirated into the handpiece, the surgeon should reduce the aspiration flow rate.
It is advisable to deflate the anterior chamber prior to introduction of the Trabectome probe. This allows blood to reflux into Schlemm’s canal from the collector channels, thereby permitting easier identification of the canal, particularly in unpigmented angles. Although the blood may drain back into the collector channels following pressurization of the eye by the irrigating Trabectome probe, the operator will have had an opportunity to identify the location of the Schlemm’s canal.
In order to minimize the risk of trauma to the crystalline lens, cornea or iris, the surgeon should hold the handpiece in such a way that the tip can be comfortably manipulated in the fingers of one hand. Electrosurgical power should never be activated when the tip of the probe is dry as this may cause damage to the handpiece.
Rotating the goniolens with one hand and the eye using the handpiece will enable a greater length of the nasal trabecular meshwork to be visualized. Thus, the potentially treatable area can be maximized.
Reflux of blood from the collector channels into the anterior chamber following removal of the irrigating handpiece from the eye is to be expected. Indeed, such reflux is regarded as a sign of correct ablation, and helps to identify the extent of ablation. The surgeon should quickly repressurize the eye to tamponade the reflux. Viscoelastic may be used as the tamponading agent if the next step is phacoemulsification. The viscoelastic is injected so as to displace blood, maintaining the red reflex for the capsulorhexis to be performed.
Following surgery, IOP-lowering drops should be continued. They may be cautiously withdrawn some weeks or months postoperatively if surgery has been performed as a drop-sparing procedure for patients who are allergic to or intolerant of one or more eye drops. Patients should be prescribed a course of topical steroids, antibiotics, and pilocarpine. The pilocarpine drops are intended to prevent the formation of peripheral anterior synechiae, which may occlude the opening in Schlemm’s canal.
Blood is commonly noted in the angle or on the iris at day 1 postoperatively. However, it has usually cleared by week 1 (Minckler et al. 2005). Patients should be counseled preoperatively that their vision may be blurred in the first week owing to the reflux of blood into the anterior chamber.
2.2.3.3 Complications
Intraoperative Complications
Poor Visibility
Excellent visibility of the area to be treated is key to the success of the procedure. The surgeon must use adequately high microscope magnification when introducing the footplate into Schlemm’s canal and when ablating tissue. Bubbles of air between the goniolens and the cornea are to be avoided through the use of sufficient coupling medium. However, care should be taken to avoid contaminating the top surface of the goniolens with the coupling medium, as this will reduce visibility. Equally, the manufacturer’s instructions for setting up the equipment need to be followed meticulously to avoid introducing air into the anterior chamber via the handpiece during the procedure. Air bubbles in the anterior chamber will block the surgeon’s view. As the handpiece’s own aspiration function is insufficient to remove intracameral air, the handpiece needs to be removed in order for the air to be exchanged first with viscoelastic and then with balanced salt solution. Surgeons are advised to avoid using the Trabectome probe with viscoelastic in the anterior chamber as this may adversely affect heat dissipation.
Insertion of Footplate
To minimize any difficulty introducing the footplate into the lumen of Schlemm’s canal, the surgeon should insert the footplate through the trabecular meshwork at a point that is not directly opposite the corneal incision. In this way, the tip of the footplate is directed obliquely (and not parallel to) the plane of the trabecular meshwork. It is also important to ensure that the tip of the footplate is not inadvertently bent or blunted by contact with hard surfaces. Particular care should be taken to avoid damaging the footplate during the removal of the plastic cap from the end of the handpiece.
Incomplete Ablation
Incomplete ablation occurs if the footplate of the probe is not introduced properly into the lumen of Schlemm’s canal. Clean ablation of tissue is thought to be important to prevent resealing and closure of Schlemm’s canal. Before starting ablation, the surgeon should verify correct placement of the footplate by gently tenting up the tissue with the probe. During ablation, the surgeon must ensure that sufficient electrosurgical power is applied. Application of insufficient power may result in tearing of the tissues and clogging of the tip with tissue. On the other hand, application of excessive power risks thermal damage to Schlemm’s canal and the orifices of the collector channels. Visible charring of tissues is an indication for treatment power to be reduced. Following ablation, the deroofed Schlemm’s canal should be visible as a shiny white gutter. It can be helpful to use the blunt heel of the footplate as a manipulator to verify that the canal has been successfully deroofed. Parts of the canal that have not been deroofed successfully may be retreated, with care to avoid thermal damage.
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