Fig. 11.1
Anterior segment-optical coherence tomography image corresponding to the right eye of a 58-year-old female undergoing preoperative assessment for combined glaucoma and KPro surgeries for a history aniridic keratopathy. Anterior chamber depth is over 3.5 mm, indicating that sufficient space exists for anterior segment placement of glaucoma drainage implant tube
The preoperative assessment of candidates for combined glaucoma and KPro surgeries also requires coordination among multiple ophthalmic subspecialists including cornea, glaucoma, vitreoretinal, and contact lens specialists. Relevant medical, social, examination, and imaging data should be reviewed preoperatively among the various subspecialists in order to derive a surgical strategy specific to each individual patient to allow for the highest chance of success while minimizing the rate of complications.
11.3 Surgical Technique
This chapter focuses on two commonly used glaucoma drainage devices: the Baerveldt tube shunt (Abbott Medical Optics Inc., Santa Ana, CA) and the Ahmed Glaucoma Valve (New World Medical, Inc., Rancho Cucamonga, CA). Surgical steps with clinical pearls are as follows [7, 8].
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1.
Traction suture
A 7-0 Vicryl suture on a cutting needle is placed partial thickness through the superior cornea such that the superior temporal quadrant is exposed.
Clinical Pearl: The traction suture should be placed closer to the limbus to ensure that it will not interfere with subsequent trephination and suturing of the corneal button.
2.
Conjunctival incision and subconjunctival/Tenon’s dissection
After making a small opening of the conjunctiva at the limbus, lidocaine 2 %, with epinephrine is injected with a 30-gauge cannula to create a plane for subsequent conjunctival dissection. Conjunctival incision is made at the limbus with two relaxing incisions on either side. Dissection is carried through Tenon’s capsule and down to bare sclera. The incision is extended for approximately 10–12 mm parallel to the limbus. Dissection at the level of bare sclera is carried posteriorly between the rectus muscles of the quadrant, first with Westcott scissors and then with curved Steven’s scissors, to create an adequate pocket for the plate. Light hemostasis is performed to avoid bleeding when suturing the plate to the sclera.
Clinical Pearl: The authors prefer a peritomy at the limbus, especially in eye with extensive conjunctival scarring. In a primary surgery, some surgeons prefer a peritomy at 2–4 mm from the limbus.
3.
Priming the tube
Ahmed Glaucoma Valve (New World Medical, Inc., Rancho Cucamonga, CA).
The Ahmed Glaucoma Valve is primed by cannulating the tube with a 30-gauge cannula on a Balanced Salt Solution (BSS)-filled syringe. BSS is slowly injected through the tube until a continuous stream of the fluid is demonstrated through valve.
Clinical Pearl: This step is crucial to ensure adequate functioning of the valve. If the initial opening pressure is extremely high, it will likely not be reached physiologically in the eye. Therefore, if this step is omitted, absolute flow restriction may occur postoperatively. Of note, forceful irrigation should be avoided.
Baerveldt Glaucoma Implant (Abbott Medical Optics Inc., Santa Ana, CA)
The tube is irrigated with a 30-gauge cannula on a BSS-filled syringe to ensure its patency. As the Baerveldt tube has no valve, it must be occluded to prevent early hypotony. A 7-0 Vicryl suture is then tied around the tube to occlude it at its base. The tube is then again cannulated with a 30-gauge cannula on a BSS-filled syringe. It is important to ensure that the tube is completely occluded to avoid immediate postoperative hypotony.
Clinical Pearl: A Vicryl absorbable suture will allow the tube to open around 5–6 weeks postoperatively. Some surgeons prefer placing a 5-0 Prolene suture in the tube lumen, as a stent or “ripcord.” A 7-0 Vicryl suture is then tied around the tube to occlude it at its base. As needed, the surgeon can then pull the ripcord in the office to allow earlier and/or more controlled opening of the tube.
4.
Inserting and suturing the plate
Clinical Pearl: The authors prefer to place the plate before corneal and retinal procedures because it is easier to manipulate and move a closed and pressurized globe.
Ahmed Glaucoma Valve (New World Medical, Inc., Rancho Cucamonga, CA).
The Ahmed Valve plate is then inserted into the superotemporal (or other intended quadrant) sub-Tenon’s pocket 8–10 mm posterior to the limbus. The valve portion of the plate should not be directly handled or it may be damaged. To fix the plate to the sclera, an 8-0 Nylon suture on a cutting needle is then placed through two fixing holes. Suture knots are rotated so they are buried.
Clinical Pearls: The plate should be at least 7 mm posterior to the limbus to decrease the risk of exposure or conjunctival erosion; however, it should not be much further back than 10 mm due to the risk of the end of the plate touching the optic nerve. In addition, caution should be used in eyes with short axial length. In general, axial length of more than 21 mm can accommodate the adult-size Ahmed. The posterior end of the FP-7 plate can be trimmed if that is a concern. In the inferonasal quadrant, the plate should not be placed further than 8 mm from the limbus due to the proximity to the optic nerve in that quadrant. Lastly, the authors prefer not to use the Pars Plana Clip (New World Medical, Inc.), which has potential for exposure and requires a very relatively large bandage contact lens (ranging from 16 to 24 mm in diameter).
Baerveldt Glaucoma Implant (Abbott Medical Optics Inc., Santa Ana, CA)
In the selected quadrant, the two rectus muscles are carefully isolated to ensure that a clear space exists between the muscle belly and the underlying sclera. The wings of the Baerveldt plate are then placed under each muscle. To fix the plate to the sclera, an 8-0 Nylon suture on a cutting needle is then placed through two fixing holes. Suture knots are then rotated so they are buried.
Clinical Pearl: In most eyes, the suture eyelets should line up at 10 mm from the limbus if the plate is appropriately positioned behind the muscles.
5.
Keratoprosthesis and Vitrectomy
Some retina surgeons prefer a view through a temporary KPro to ensure a complete shaving for the vitreous base in the desired quadrant. In this case, the steps will be temporary KPro, PPV, removal of the temporary KPro and then Boston KPro placement. Other retina surgeons may perform PPV through Boston KPro. In this case, the steps will be Boston KPro placement, and then PPV. This technique requires scleral depression for optimal visualization of the vitreous base.
Clinical Pearls: It is recommended to shave vitreous base 360° because many of these eyes may require a future second GDI. In many eyes that require KPro, a landmark for the limbus may be difficult to discern. In this case, transillumination and/or direct visualization will aid a safe introduction of a 23-gauge needle in the posterior part of the pars plana (approximately aiming for 4–5 mm from the limbus).
6.
Inserting the tube into the anterior chamber
The tube is then trimmed to an appropriate length (approximately 4 mm from the entry to allow visualization of the tube behind the keratoprosthesis). The tube may be trimmed bevel down to decrease risk of contact/occlusion with the iris and/or KPro device. To avoid tube kinking, the tangential scleral entry for the tube (pointing slightly anteriorly) is created at 4–5 mm from the limbus using a 23-gauge needle. After the tube is inserted through the scleral entry, the tip of the tube should be visualized behind the KPro. The tube is secured to the sclera with a 10-0 Nylon mattress suture.
Clinical Pearl: Visualize the needle at all times. The authors prefer not to use the scleral entry from the vitrectomy port because most of them are too large for the tube causing excessive leakage around tube that may lead to early hypotony.
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