IIA Trabecular Outflow Procedures A 60-year-old woman with primary open-angle glaucoma (POAG) presents with worsening visual acuity in both eyes, particularly with disabling glare while driving. Best-corrected visual acuity is 20/40 in each eye, with glare testing resulting in worsening to 20/70 in both eyes. Intraocular pressure (IOP) on latanoprost and timolol both administered in both eyes once a day is 20 mm Hg in the right eye and 23 mm Hg in the left eye. Anterior segment biomicroscopic examination is significant for 2 to 3+ nuclear sclerosis of the lens with cortical spoking in both eyes. Funduscopic examination shows a cup-to-disk ratio of 0.6 in the right eye with an intact neuroretinal rim and 0.75 in the left eye with inferior thinning of the neuroretinal rim. Humphrey visual field (HVF) testing shows a normal examination in the right eye and an early superior arcuate defect in the left eye (Fig. 22.1). The patient is recommended to have phacoemulsification cataract extraction, beginning with the right eye. Postoperatively, visual acuity is improved to 20/20 after correction, with a dramatic improvement in glare testing. IOP is also improved to 15 mm Hg on latanoprost alone in the right eye and 17 mm Hg on latanoprost and timolol in the left eye at 1-year follow-up. Subsequent visual field testing has shown no demonstrable progression in either eye. Cataract surgery is one of the most commonly performed surgeries in the United States, with 3 million procedures performed each year.1 Since the introduction of phacoemulsification in 1967 by Charles Kelman, this technique has supplanted extracapsular cataract extraction in the Western world, having been used for more than 97% of all cataract surgeries performed in the United States since 2007.2 Ultrasonic power delivered by an intraocular probe emulsifies and removes the nuclear portion of a cataract, allowing the use of small clear corneal incisions and obviating the need for large scleral incisions that require closure with sutures and violate the subconjunctival space. This preservation of the conjunctiva is of vital importance in patients with glaucoma. Because both cataract and glaucoma tend to increase in prevalence with age, it is quite common for glaucoma patients to have some degree of cataract formation. Cataractous lenses can affect both the ability to perform accurate surveillance for glaucomatous progression as well as impact the aqueous outflow. Funduscopic examinations of the optic nerve can become more difficult as the opacity from cataract worsens. Additionally, cataractous lenses have been shown to significantly impact both structural glaucoma tests such as optical coherence tomography (OCT) and functional tests such as automated static perimetry. For example, an increase in retinal nerve fiber layer (RNFL) thickness as well as signal strength as measured by spectral domain OCT can be seen after cataract surgery.3 Similarly, a significant improvement in mean deviation on visual field testing can occur after cataract removal, partially resulting from elimination of lens-induced artifact.4 Performing early cataract surgery also offers several therapeutic advantages for glaucoma patients. It eliminates the future risk of one of the most common adverse effects of many glaucoma procedures—the development of a cataract. Approximately 20% of patients randomized to initial glaucoma surgery in the Collaborative Initial Glaucoma Treatment Study (CIGTS) required cataract extraction, with the leading cause of cataract formation being trabeculectomy.5 As many as 50% of eyes develop a visually significant cataract within 5 years of trabeculectomy or tube shunt surgery.6,7 Phacoemulsification prior to a glaucoma procedure, particularly trabeculectomy, is far preferable to phacoemulsification after establishment of a functioning bleb that is at risk following cataract removal. Husain et al,8 in a study of 235 glaucoma patients who underwent trabeculectomy, found that the sooner cataract surgery was performed after trabeculectomy, the higher the likelihood of trabeculectomy failure. In this study, failure was defined as IOP greater than 21 mm Hg, and the hazard ratios for risk of trabeculectomy failure at 6 months, 1 year, and 2 years were 3.00, 1.73, and 1.32, respectively. Similarly, Sałaga-Pylak et al9 retrospectively showed that eyes that underwent cataract extraction after trabeculectomy had a 20% lower success rate compared with those that did not require cataract extraction. Both bleb size and elevation were found to deteriorate after cataract surgery. Possible mechanisms of bleb failure after cataract surgery include increased permeability of the blood–aqueous barrier, leading to increased inflammation and subsequent bleb fibrosis. Perhaps more importantly, as shown by numerous studies over the past few decades, cataract extraction leads to sustained reduction in IOP in patients with POAG) ocular hypertension, and primary angle-closure glaucoma (PACG). In 2002, Friedman et al10 reported a 2 to 4 mm Hg reduction in IOP following cataract surgery in POAG eyes. Matsumara et al11 prospectively showed an average IOP reduction of 1.5 mm Hg, 2.5 mm Hg, and 5.5 mm Hg in normal, controlled POAG (preoperative IOP < 21), and uncontrolled POAG (preoperative IOP ≥ 21) individuals, respectively, at 3 years following cataract surgery. There are also compelling data supporting cataract extraction as a means of lowering IOP in ocular hypertensive patients. Mansberger et al12 analyzed data from the Ocular Hypertension Treatment Study (OHTS) and found that participants who underwent cataract extraction had an IOP reduction of 16.5% at 3 years. Compared with POAG patients, PACG patients often can achieve greater IOP reduction after cataract surgery. In a comparison of PACG and POAG subjects 2 years after cataract surgery, Hayashi et al13 found both a larger magnitude of IOP reduction (6.9 mm Hg vs 5.5 mm Hg, respectively) and less medication dependence (40% vs 19.1% medication free, respectively) in the former group. Patients with POAG, PACG, or ocular hypertension can potentially benefit from cataract surgery for both diagnostic and therapeutic purposes. To determine which patients may benefit the most, it is useful to explore the possible mechanisms resulting in IOP reduction after removal of a cataract. In patients with PACG, cataract extraction relieves pupillary block, leading to deepening of the anterior chamber and improved access to the trabecular meshwork.14 Euswas and Warrasak15 found that the magnitude of IOP reduction was related to the degree of angle closure, as eyes with less than 270 degrees of peripheral anterior synechiae (PAS) experiencing a 3 mm Hg greater IOP reduction compared with eyes with less than 180 degrees of PAS.15 Issa16 developed a novel model to predict IOP reduction based on the ratio of preoperative IOP to anterior chamber depth (PD ratio). In general, the higher the preoperative IOP and the shallower the anterior chamber depth, the greater the IOP reduction following cataract extraction. Eyes with a PD ≥ 6.0 exhibited a mean IOP reduction of 4.90 mm Hg, whereas those with a PD < 6.0 had a more modest but still significant IOP reduction of 1.64 mm Hg. In patients with POAG and ocular hypertension, the mechanism of IOP reduction after cataract surgery is less clear, and various hypotheses have been proposed. Kim et al17 have theorized that high fluid flow during phacoemulsification may remove deposition of glycosaminoglycans in the trabecular meshwork. Tong and Miller18 have postulated that microtrauma to the trabecular meshwork may produce an inflammatory effect akin to that seen after laser trabeculoplasty. Other proposed mechanisms include biochemical or blood–aqueous barrier alteration, ciliary body traction via posterior pressure on zonules intraoperatively leading to prevention of collapse of Schlemm’s canal, and enhanced outflow due to stretching of the trabecular meshwork.19–21 In terms of which POAG patients can expect the greatest IOP reduction, Poley22 found that the greater the preoperative IOP, the greater the IOP reduction. Eyes with a preoperative IOP in the range of 23 to 31 mm Hg, 20 to 22 mm Hg, 18 to 19 mm Hg, and 15 to 17 mm Hg had IOP reductions of 6.5 mm Hg, 4.8 mm Hg, 2.5 mm Hg, and 1.6 mm Hg, respectively. Interestingly, eyes that had a preoperative IOP of 9 to 14 mm Hg did not have an IOP reduction, instead having a marginal increase in IOP of 0.2 mm Hg. In summary, although cataract surgery is beneficial for the vast majority of glaucoma patients, those with the higher preoperative IOP, shallower anterior chamber, and narrower angle tend to have the greatest magnitude and longest duration of IOP reduction. Surgeons must consider several issues regarding standard phacoemulsification when performing cataract surgery on glaucoma patients. In patients who have had prior glaucoma filtration surgery, the timing of cataract surgery is important. As mentioned previously, Husain et al8 have demonstrated that there is a higher risk of trabeculectomy failure the sooner the cataract surgery is performed following the glaucoma procedure. Thus, cataract surgery should be delayed as long as possible following trabeculectomy without jeopardizing ocular health to decrease the risk of trabeculectomy failure. There are some specific best practices with regard to cataract surgery in the glaucoma patient. Clear corneal incisions should be made whenever possible to avoid violating the conjunctival space, which is important to preserve for possible future glaucoma surgery. It is important to thoroughly remove all viscoelastic material at the conclusion of the procedure to reduce the risk of postoperative IOP spike. Consideration should be given to perioperative oral carbonic anhydrase inhibitors to further reduce this risk in select patients who are at risk of IOP spike-related glaucomatous damage in the early postoperative period. Alternatively, intracameral injection of miotic agent at the end of surgery can help prevent elevated IOP in addition to reversing the dilation. As newer intraocular lenses (IOLs) are being developed, more options are available for optimal refractive correction with cataract surgery. However, patients with glaucoma may not be ideal candidates for certain types of implantable lenses. Multifocal IOLs are designed to provide multiple simultaneous images from different focal points onto the retina, relying on the fact that pupils constrict for near work and that different optical zones in the center and periphery of the IOL can be used for different tasks. Based on this design, however, there are some limitations, including unwanted photic phenomenon such as haloes or glare, but most importantly decreased contrast sensitivity. Because both multifocal IOLs and glaucomatous optic neuropathy decrease contrast sensitivity, glaucoma may be considered a relative contraindication for multifocal IOL placement. In contrast to multifocal IOLs, accommodating IOLs are monofocal and rely on replicating the physiological accommodating mechanism to provide near and intermediate vision.23 Because they are monofocal IOLs, contrast sensitivity is not an issue. However, eyes with weakened zonules are likely to be poor candidates for accommodating IOLs because they also may have a compromised accommodative reflex. Toric IOLs are designed to correct for corneal astigmatism, and IOL stability is important, because rotation can result in loss of astigmatism correction, or when severe, result in induced astigmatism.24 Thus, similar to accommodating IOLs, toric IOLs should be used with caution in patients with weakened zonules, as IOL decentration can compromise visual acuity. Pseudoexfoliation, a common cause of secondary open-angle glaucoma, presents several potential intraoperative challenges, including small pupils, zonular instability with resultant difficulty completing a capsulorrhexis, posterior capsular laxity, and unstable capsular support for IOL placement, that require modification of surgical technique. Poor pupillary dilation may lead to a suboptimally sized capsulorrhexis, which in turn can make subsequent steps more difficult and increase the risk of further zonular compromise, vitreous loss, and postoperative capsular phimosis.25 Various techniques and adjunctive surgical devices are available to facilitate a larger pupil, including mechanical stretching, pupil expansion rings, and iris retractors (Figs. 22.2 and 22.3). Surgeon preference dictates which technique to use in each case. In addition, staining of the anterior capsule with trypan blue can greatly improve visibility of the anterior capsule during capsulorrhexis (Fig. 22.4). Zonular instability may present preoperatively as iris flutter, iridodonesis, phacodonesis, or frank lens subluxation and zonular dialysis. In other cases, though, it may only manifest intraoperatively with difficulty initiating a capsular tear, anterior capsular striae, and movement of the capsular bag during capsulorrhexis, posterior capsular laxity, and striae during cortical removal, or vitreous prolapse around an intact capsular bag. Fortunately, the use of intraoperative devices to improve capsular support can greatly enhance a surgeon’s ability to safely complete cataract surgery. Capsular retractors are modified iris retractors designed to be placed at the edge of a continuous curvilinear capsulorrhexis to provide adequate intraoperative support for the capsular bag during lens extraction (Fig. 22.5). Placement of capsular tension rings or segments can provide both intraoperative and, perhaps more importantly, postoperative support to the capsular bag. An endocapsular tension ring (CTR) is a circular polymethylmethacrylate (PMMA) device that expands the capsular fornix and spreads zonular tension evenly among the remaining intact zonules (Fig. 22.5). It is most useful in cases of mild zonulopathy, defined as an arc of no more than four hour positions on a clock face (≤ 120 degrees) of zonular loss.25 A CTR can be placed at any time during surgery, but early placement may complicate cortical removal. An intact capsular bag and continuous curvilinear capsulorrhexis is required for placement of a CTR. With greater degrees of zonular loss, sutured devices such as a Cionni modified CTR (mCTR) or a capsule tension segment (CTS) are often useful.
22 Phacoemulsification Cataract Extraction
Case Presentation
The Procedure
Rationale Behind the Procedure
Patient Selection
Surgical Technique
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