Know your glaucoma surgery for better comanagement

Treating and managing chronic glaucoma can be rewarding as an optometrist. The frequency of office visits to monitor this chronic disease provides ODs an opportunity to develop a close relationship with their patients while providing medical eye care. More than ever, patients are looking to optometrists to manage all of their glaucoma care, including postoperative management of glaucoma surgical procedures.

Recent advances in microinvasive surgical techniques and devices that improve aqueous outflow have revolutionized the surgical glaucoma treatment algorithm. It is critical that optometrists become knowledgeable in all the surgical glaucoma options available to patients so they can facilitate and coordinate care with a glaucoma specialist when their intervention is necessary. It is also important to establish a relationship with your local glaucoma specialist if you are planning to comanage surgery. I recommend observing them in their clinic and during surgery in order to get to know their surgical techniques and management preferences. This also will build mutual trust when comanaging patients because glaucoma management carries higher liability for both parties. If you and your surgeon are not on the same page about postsurgical treatment and management, it can leave you both open to increased risk of litigation, especially in cases of advanced glaucoma.

Laser iridotomy in narrow-angle or angle-closure glaucoma

Laser peripheral iridotomy (LPI) is the definitive treatment for angle-closure glaucoma (ACG) due to pupillary block as well as ACG preventative treatment in those with narrow angles.

In patients presenting with ACG, an LPI should be performed after you have broken the attack using oral and topical agents. Initiate an in office “glaucoma cocktail” and give 500 mg of oral acetazolamide (Diamox, Wyeth). Then add one drop of topical glaucoma agents of each pharmaceutical class every 10 minutes until the pressure starts to fall below 30 mm Hg. The glaucoma surgeon and the patient alike will appreciate you for breaking the attack prior to seeing the surgeon same day.

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An LPI establishes an alternative route for aqueous flow between the anterior and posterior chambers and is typically done using a YAG laser which allows quicker penetration with less total energy.¹ After diagnosing narrow angles with gonioscopy, you need to determine whether the angles are at risk for closure. If the iris is touching the trabecular meshwork, there is risk of closure, and the patient should be referred for an LPI.

The patient is given 1% pilocarpine and either brimonidine (Aphagan P, Allergan) or aproclonidine (Iopidine, Alcon) 10 minutes prior to the LPI to prevent postoperative intraocular pressure (IOP) spike. Many surgeons are now placing the iridotomies temporal to reduce linear dysphotopsias postoperatively.² (See Figure 1.) Despite location under the lid for superior and inferior PIs, it is hypothesized the tear prism at the edge of the lids bend light, allowing it to reflect back through to the retina, causing glare.³ After the patient has the LPI, he will be placed on a topical anti-inflammatory for five to seven days to prevent postoperative inflammation. The surgeon will recheck IOP one hour later to ensure no spike and return the patient to you in one week pending no complications. 

At the one-week follow up, look for patency of the iridotomies. This can be done by retro illumination. If the iris was dense, or a localized bleed prevented visualization during the procedure, the iridotomy may not achieve patency. Refer back to the surgeon for repeat treatment if nonpatent. Late closure can also occur up to six weeks postoperatively.⁴ Gonioscopy is also performed to ensure the angle has opened. If the angle has not opened or IOP remains elevated, then plateau iris is suspected. The patient should be referred back to the surgeon for argon laser iridoplasty. 

ODs should then evaluate for adjunctive topical therapy based on the amount of glaucomatous damage at discovery. Clinical correlation of disc assessment, visual fields, and nerve fiber layer evaluation is critical in determining if IOP is ideal to prevent further change over time.

Next: Selective laser trabeculoplasty (SLT)

Selective laser trabeculoplasty (SLT)

SLT is the easiest of all the glaucoma surgeries to comanage due to lower risk of complication as well as efficacy. SLT uses a Q-switched, three-nanosecond, frequency-doubled Nd:YAG; 532-nm wavelength green laser to selectively target nonpigmented cells of the trabecular meshwork (TM). This spares adjacent cells from thermal heat transfer and damage. Activated cells release cytokines that trigger a targeted macrophage response which phagocytize matter in the TM, increasing outflow.⁵ The average reduction in IOP has been reported from 18 percent to 40 percent, similar to prostaglandin analogs.⁶  SLT can be used as adjunct therapy or as a primary treatment to lower IOP. 

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The patient is given a drop of a topical alpha-agonist before and after SLT to prevent an acute rise in IOP. The trabecular meshwork is treated 360 degrees for best results, but a treatment of 180 degrees, especially if the TM is heavily pigmented, can also be effective with less risk of IOP spike. After the procedure, patients are placed on a short regimen of topical steroids or NSAIDs to prevent inflammation. The patient is returned to the referring doctor either at one week or six weeks. The surgeon checks the patient for an IOP spike immediately after surgery. If there are no immediate complications, the patient can wait to be seen at six weeks because maximum IOP lowering is not achieved until then. If the patient is currently on topical therapy, he is kept on those glaucoma meds until six weeks postop. The comanaging doctor can then adjust the medications based on IOP goal. 

Many surgeons will not perform SLT on the second eye until it is known whether the patient responded to SLT in the first eye. At six weeks, the optometrist can then schedule SLT on the second eye if indicated. If the patient’s IOP does not respond to SLT, then glaucoma medications or other procedures will be needed.

SLT can lose its effectiveness over time, and IOP may rise. Success rates of SLT one-, three-, and five-year follow-up were 68 percent, 46 percent, and 32 percent, respectively.⁷ Studies have shown that IOP reduction with the second treatment is less, with an average decrease of 2.9 mm Hg compared to >5 mm Hg with the initial treatment.⁸  Some surgeons repeat SLT, but there are no long-term studies on efficacy of repeat SLT. 

Next: MIGS and iStent

MIGS and iStent

Recent advances in micro-invasive glaucoma surgical (MIGS) techniques and devices that improve aqueous outflow have revolutionized the glaucoma treatment algorithm. (See Table 1.) The Trabecular Micro-Bypass Stent from Glaukos (iStent) is a tiny L-shaped implantable device made of titanium that is 1-mm long and 0.33-mm high.^9,10 (See Figure 2.) It is approved only for use in combination with cataract surgery. The stent creates a patent bypass between the anterior chamber and Schlemm’s canal to improve aqueous outflow. It is inserted easiest inferonasally in Schlemm’s canal, where coincidentally the highest concentration of collecting channels and aqueous veins are located_.^9,10 The procedure is done under gonioscopic visualization before or after the cataract procedure, so visualization of the anatomy of the angle is critical.

Related: How patients perceive their glaucoma matters

Postoperatively, glaucoma medications are continued initially, and patients follow the same regimen of topical medications used for cataract surgery. It takes at least six weeks to reach the maximum IOP-lowering effect from iStent. Don’t be over eager in stopping glaucoma medications. Once the IOP decreases, glaucoma medications can be reduced one at a time until desired IOP goal is obtained.

In clinical trials, 68 percent of patients undergoing a combined iStent/cataract surgery procedure achieved an IOP of 21 mm Hg or lower with no medications at one year compared with only 50 percent of subjects in the cataract surgery-alone group. This treatment difference of 18 percent was statistically (P=0.004) and clinically significant. In the study, a 20 percent IOP reduction at 12 months was observed in 64 percent of patients in the iStent group vs. 47 percent in the cataract surgery-alone group (P=0.01).¹⁰

Next: Filtration surgery

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. 

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References

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2. Vera V, Naqi A, Belovay GW, Varma DK, Ahmed II. Dysphotopsia after temporal versus superior laser peripheral iridotomy: a prospective randomized paired eye trial. Am J Ophthalmol. 2014 May;157(5):929-35.

3. Murphy PH, Trope GE. Monocular blurring. A complication of YAG laser iridotomy. Ophthalmology. 1991 Oct;98(10):1539-42.

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7. Juzych MS, Chopra V, Banitt MR, Hughes BA, Kim C, Goulas MT, Shin DH. Comparison of long-term outcomes of selective laser trabeculoplasty versus argon laser trabeculoplasty in open angle glaucoma. Ophthalmology. 2004 Oct;111(10):1853-9.

8.  Hong BK, Winer JC, Martone JF, Wand M, Altman B, Shields B. Repeat selective laser trabeculoplasty. J Glaucoma. 2009 Mar;18(3):180-3.

9. Samples JR, Ahmed IIK, Eds. Surgical Innovations in Glaucoma. New York: Springer, 2014:147-156.

10. Samuelson TW1, Katz LJ, Wells JM, Duh YJ, Giamporcaro JE; US iStent Study Group. Randomized evaluation of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology. 2011 Mar;118(3):459-67.

11. Weinreb RN, Crowston, JG. Glaucoma Surgery: Open Angle Glaucoma. The Hague, Netherlands: Kugler Publications. 2005.

12. Allingham RR, Damji KF, Freedman SE, Rhea DJ, Shields MB. Shields Textbook of Glaucoma. Philadelphia: Lippincott Williams and Wilkins, 2011.

13. Gedde SJ, Schiffman JC, Feuer WJ, Herndon LW, Brandt JD, Budenz DL; Tube Versus Trabeculectomy Study Group. Three-year follow-up of the tube versus trabeculectomy study. Am J Ophthalmol. 2009 Nov;148(5):670-84.

14. Schrieber C, Liu Y. Choroidal effusions after glaucoma surgery. Curr Opin Ophthalmol. 2015 Mar;26(2):134-42.

15. Christakis PG, Tsai JC, Kalenak JW, Zurakowski D, Cantor LB, Kammer JA, Ahmed II. The Ahmed versus Baerveldt study: three-year treatment outcomes. Ophthalmology. 2013 Nov;120(11):2232-40.

16. Souza C, Tran DH, Loman J, Law SK, Coleman AL, Caprioli J. Long-term outcomes of Ahmed glaucoma valve implantation in refractory glaucomas. Am J Ophthalmol. 2007 Dec;144(6):893-900

17. Nouri-Mahdavi K1, Caprioli J. Evaluation of the hypertensive phase after insertion of the Ahmed Glaucoma Valve. Am J Ophthalmol. 2003 Dec;136(6):1001-8.

18. Law SK. Earlier Intraocular Pressure Control After Ahmed Glaucoma Valve Implantation for Glaucoma. ClinicalTrials.gov. Available at: https://clinicaltrials.gov/ct2/show/NCT00869141. Accessed 3/24/16.

19. Gedde SJ, Schiffman JC, Feuer WJ, Herndon LW, Brandt JD, Budenz DL; Tube versus Trabeculectomy Study Group. Treatment outcomes in the Tube Versus Trabeculectomy (TVT) study after five years of follow-up. Am J Ophthalmol. 2012 May;153(5):789-803.

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