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    Know your glaucoma surgery for better comanagement

    Patients are looking more to ODs to manage their glaucoma care, including postop

     

    Filtration surgery

    Recommendation for filtration surgery is necessary when glaucoma progresses despite all other efforts exhausted. Indications are worsening visual fields or cupping despite IOP at episcleral venous pressure, the IOP not at goal despite maximum meds or SLT/MIGS, or poor compliance or intolerance to drops. Will the patient go blind in her lifetime if surgery is not performed? If the answer is yes, then it is time to refer for a trabeculectomy or aqueous drainage device.11

    Trabeculectomy. Trabeculectomy is the most common filtering operation. It lowers IOP by creating a fistula between the inner eye and subconjunctival space. The surgeon first dissects a conjunctival flap superiorly. Tenon’s capsule is cut, and a scleral flap is then created. The surgeon applies an antimetabolite such as mitomycin-C to the scleral flap to prevent fibroblast proliferation and subsequent scarring. Next, a sclerectomy is created to allow for aqueous drainage through the scleral flap. Finally, an iridectomy is done to prevent obstruction of the sclerectomy. The scleral flap is closed with sutures, and the tightness of the suture regulates aqueous flow to create a bleb. The conjunctiva is then sutured back in place.12 Patients are placed on a topical antibiotic and steroid four times a day. All glaucoma drops are discontinued in the surgical eye.

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    The goal is to establish an elevated bleb early on and reduce the risk of bleb failure by scarring. Topical steroids are used the first three months. You should not taper the steroid until the injection of the surgical eye matches the injection of the nonsurgical eye. It is critical to avoid bleb failure due to scarring from inflammation. Each surgeon has different preferences regarding postoperative steroid management, so it is important to closely communicate with the glaucoma specialist.

    One of the more common early postoperative complication is hypotony.13 The clinician needs to determine if hypotony is due to a wound leak, over filtration, or a decrease in aqueous production. If over filtering, the bleb will look giant. If the bleb looks small or flat, it is most likely due to a decrease in aqueous production. If a leak is present, decrease the steroid to once a day and consider placing a large-diameter contact lens on to cover the leak. If over filtering, also decrease the steroid and add topical atropine twice a day.

    It is critical to look for a shallow anterior chamber. Simultaneously, you may see a choroidal detachment or effusion, which is from fluid in the suprachoroidal space. This pushes the lens-iris diaphragm forward and further flattens the chamber. If there is a shallow anterior chamber secondary to the over filtration, the cycloplegic agent will move the lens iris diaphragm back and help the ciliary body restart the production of aqueous. See the patient back in one to two days, and if the anterior chamber remains shallow, refer back to the surgeon. The surgeon may need to perform a bleb injection with an ophthalmic viscosurgical device (OVD) to slow down filtration.

    Choroidal effusions typically resolve on their own, but in about 20 percent of cases, they may need to be drained.14 Check the patient every week—as long as the anterior chamber is not too shallow—until the hypotony improves. On the contrary, if IOP is high and not at goal after surgery, the sutures may need to be adjusted through laser suture lysis.

    Aqueous drainage devices. These devices reroute aqueous from the anterior chamber to an external reservoir where a fibrous bleb forms and regulates flow by diffusion out the capillaries. These devices have shown success in controlling IOP in eyes with previously failed trabeculectomy, uveitic, and neovascular glaucomas.13

    Glaucoma drainage devices are available as nonvalved (free flow) or valved (resisted flow). Baerveldt  (AMO) or Molteno (Molteno Ophthalmic) tubes are the most common non-valved devices and are usually ligated with a dissolvable suture to prevent early hypotony until the bleb forms four to six weeks postoperatively. The Ahmed (New World Medical) device is the most common valved tube. It has flow resistant leaflets similar to cardiac valves. (See Figure 3.) The valve automatically closes if the IOP is too low. The valved devices reduce the risk of early postoperative hypotony, but postoperative target pressure may be higher than with the non-valved devices.15

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    Topical antibiotic and steroid therapy is similar to trabeculectomy protocol. With Ahmed devices, the IOP can climb after one week. This is called a hypertensive phase which typically stabilizes to lower IOP levels after four to five months.16,17 With all devices, the initial goal is to keep pressure in the teens.  Add back topical glaucoma meds when you see IOP start to climb. Topical beta blockers, alpha agonists, and carbonic anhydrase inhibitors are the best initial choices.18 With nonvalved tubes, glaucoma medications are also needed early on until the suture dissolves and the filter starts working.

    Early complications can include hyphema, diplopia from plate placement by the recti muscles, hypotony, and encapsulation. 19 Corneal decompensation from the tube can occur late onset and may require transplantation.19

    Optometrists are uniquely qualified to provide primary medical and postoperative glaucoma care. Utilizing surgical options earlier in the glaucoma continuum and understanding their postoperative management is necessary to prevent severe vision loss from this disease. Close collaboration with the glaucoma specialist is critical in maintaining continuity of care for your patients. 

    Click here to check out the latest glaucoma news and advice

    Elizabeth D. Muckley, OD, FAAO
    Dr. Muckley is director of optometric services at NE Ohio Eye Surgeons in Kent, OH, where she concentrates on medical glaucoma and ...

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