|GLAUCOMA SURGERY UPDATE
|Year : 2015 | Volume
| Issue : 1 | Page : 10-17
Cataract surgery in the glaucoma patient
Jennifer S Kung, Daniel Y Choi, Anjum S Cheema, Kuldev Singh
Byers Eye Institute, School of Medicine, Stanford University, California, USA
|Date of Web Publication||1-Jan-2015|
2452 Watson Court; Palo Alto, CA 94303
Source of Support: None, Conflict of Interest: None
| Abstract|| |
To summarize the role of cataract surgery in the glaucoma patient, in terms of the effect on intraocular pressure (IOP) as well as diagnostic and therapeutic considerations for those with both conditions. Recent evidence suggests that cataract extraction may produce a significant and sustained IOP reduction in individuals with open-angle glaucoma, ocular hypertension, and angle-closure glaucoma. Cataract removal may improve the practitioner's ability to interpret perimetric testing, and re-establishing perimetric and optic nerve imaging baselines is recommended after cataract surgery. The sequence of cataract surgery relative to glaucoma surgery impacts the likelihood of complications and surgical success. There are multiple benefits to perform cataract surgery prior to glaucoma surgery while cataract surgery after trabeculectomy increases the risk of subsequent filtration failure. As "minimally invasive glaucoma surgeries" continue to improve in terms of efficacy, there is an evolving role for combined cataract and glaucoma surgery in patients with early to moderate stages of glaucoma.
Keywords: Cataract, Glaucoma, Surgery
|How to cite this article:|
Kung JS, Choi DY, Cheema AS, Singh K. Cataract surgery in the glaucoma patient. Middle East Afr J Ophthalmol 2015;22:10-7
| Introduction|| |
Over the past century, the burden of cataract and glaucoma has been increasing and can only be expected to grow as the population ages worldwide. In a survey of the Middle East and North Africa in 2010, cataract was the leading cause of blindness (23.4%), while glaucoma accounted for a significant percentage (9.6%), exceeded only by refractive error (13.1%) and macular degeneration (10.3%).  Recent World Health Organization reports from 2002 highlight cataract and glaucoma as the two greatest sources of visual impairment worldwide, with 17 (47.8%) and 4.4 million (12.3%) persons affected, respectively.  Models based on UN world population projections predict that in the year 2020, 79.6 million persons will be afflicted with either open-angle glaucoma (OAG) or angle-closure glaucoma (ACG) with 5.9 million and 5.3 million projected to be bilaterally blind from these two conditions, respectively.  Africa, in particular, has the highest prevalence of glaucoma in the adult population compared to all other geographic regions worldwide. 
In light of this growing scourge of visual impairment, it is of no small importance that cataract surgery is evolving as a primary means of reducing intraocular pressure (IOP), effectively "killing two birds with one stone." IOP is the sole modifiable risk factor in glaucoma progression. Recent studies of cataract surgery in glaucoma patients have demonstrated IOP reduction of 2-4 mmHg lasting for at least 3 years following cataract surgery. ,, This sustained IOP reduction highlights cataract surgery as a valuable supplement to the preexisting armamentarium of tube shunt surgery and trabeculectomy, with its enhanced safety profile relative to traditional glaucoma surgeries making it an attractive choice for select patients, particularly those without severe glaucomatous disease. There is a compelling body of evidence showing both why and how cataract surgery should be applied to specific subsets of patients with glaucoma - primary OAG (POAG), ACG and pseudoexfoliation (PXE).
In addition, several newer nonpenetrating glaucoma procedures, the so-called "minimally invasive glaucoma surgeries" (MIGS), have been developed to be performed in conjunction with cataract surgery. These procedures have the potential to yield additional IOP reduction beyond what cataract surgery alone can provide.
| Cataract Surgery and Primary Open-Angle Glaucoma|| |
Numerous studies over the past few decades have shown that cataract surgery leads to a sustained decrease in IOP in POAG patients. As early as the 1970s, Bigger and Becker observed decreased IOP in patients undergoing uncomplicated intracapsular cataract extraction.  In the mid-1990s, Matsumura et al. prospectively followed 93 eyes and found that cataract surgery lowered IOP an average of 1.5 mmHg at 3 years.  Shingleton et al. carried the follow-up out to an average of 5 years in a cohort of POAG patients, glaucoma suspects and normal patients. After phacoemulsification, these patients experienced IOP decreases of 1.8 mmHg, 1.3 mmHg, and 1.5 mmHg, respectively.  A 2002 Cochrane literature review by Friedman et al. reported a consistent (albeit weak) 2-4 mmHg reduction in IOP by either phacoemulsification or extracapsular cataract extraction. 
There is a direct relationship between the preoperative level of IOP and the subsequent IOP reduction: The higher the initial IOP, the greater the magnitude of the IOP reduction following surgery. Matsumura et al. highlighted this relationship, showing that although the average IOP reduction was 1.5 mmHg at 5 years for all study subjects, patients with a preoperative IOP ≥ 21 mmHg had a 5.5 mmHg of reduction in IOP. Patients with a preoperative IOP < 21 mmHg had a 2.5 mmHg reduction in IOP and normal controls showed a 1.5 mmHg reduction.  Poley et al. corroborated that greater postoperative IOP reductions could be expected in patients with higher preoperative IOPs. They showed a 6.5 mmHg decrease in the 23-31 mmHg preoperative group, a 4.8 mmHg decrease in the 20-22 mmHg preoperative group, a 2.5 mmHg decrease in the 18-19 mmHg group, a 1.6 mmHg decrease in the 15-17 mmHg group, and a 0.2 mmHg increase in the 9-14 mmHg preoperative group.  Clearly, preoperative IOP is a strong predictor of postoperative IOP reduction.
| Cataract Surgery and Ocular Hypertension|| |
There is compelling evidence to make a case for cataract surgery in the reduction of IOP in ocular hypertensive patients. Drawing data from the landmark Ocular Hypertension Treatment Study (OHTS), Mansberger et al. analyzed the observation arm of OHTS, comparing 42 participants (63 eyes) who underwent cataract surgery during the study to a control group of 743 participants (743 eyes) who did not undergo such surgery. For at least 3 years following surgery, postoperative IOP was significantly lower than preoperative IOP with a mean decrease of 16.5%. In addition, 39.7% of eyes maintained postoperative IOP reduction ≥ 20% below the preoperative baseline. 
| Cataract Surgery and Pseudoexfoliation|| |
After POAG, PXE is the second leading cause of OAG in the world. , Although it was traditionally classified as a disease of northern latitudes, recent studies have found that the burden is also particularly high in regions of Africa.  Fibrillar material accumulates with age, depositing on various anterior segment (AS) structures and blocking drainage through the trabecular meshwork. Not only there is an increased incidence of cataract in PXE eyes, but also poor pupillary dilation and zonular instability can result in complicated cataract surgery. , In a retrospective review of 1122 eyes, Shingleton et al. found that PXE eyes without glaucoma sustained a significant reduction in IOP for 7 years after cataract surgery. Moreover, while PXE eyes with glaucoma had a significant reduction for only 1-year, there was a reduced necessity for glaucoma medications up to 6 years following surgery.  A longitudinal review of 339 PXE patients over 21 years showed that patient who underwent cataract extraction did not have a change in IOP, while those that remained phakic could expect a 0.05 mmHg increase in IOP each year. 
| Cataract Surgery and Narrow Angle Glaucoma|| |
While cataract surgery is effective in lowering IOP for patients with POAG, the impact of this procedure is even greater in patients with ACG. Estimates from 2010 identified 15 million persons with primary ACG, accounting for 50% of blindness caused by glaucoma.  ACG patients experience both a greater duration and magnitude of IOP-lowering effect when compared to their POAG counterparts. Comparing 74 chronic angle-closure glaucoma (CACG) and 68 POAG patients, Hayashi et al. found that CACG patients had a mean 6.9 mmHg IOP reduction versus 5.5 mmHg in POAG patients following cataract surgery. CACG patients also required fewer postoperative glaucoma medications (40.0% CACG vs. 19.1% POAG were medication-free, respectively).  In particular, CACG eyes with a greater extent of peripheral anterior synechiae and more advanced glaucomatous optic neuropathy benefit most from cataract extraction. 
Phacoemulsification has been compared to both peripheral iridotomy and trabeculectomy as a means of lowering IOP in patients with ACG in several studies. In a study of acute primary angle-closure patients, Husain et al. randomized eyes to either laser peripheral iridotomy (LPI) or phacoemulsification with posterior chamber intraocular lens (Phaco/IOL) implantation. At 2 years postprocedure, only 61.1% of the LPI group compared to 89.5% of the Phaco/IOL group survived without failure, as defined as IOP between 22 and 24 mmHg on two occasions (readings taken within 1-month of each other) or IOP ≥ 25 mmHg on any one occasion after postoperative weeks 3.  Tham et al. prospectively compared phacoemulsification to trabeculectomy with adjunctive mitomycin C (MMC) in 50 medically uncontrolled CACG eyes. At 2 years, there was a comparable total IOP reduction - 8.4 mmHg (34%) following phacoemulsification versus 8.9 mmHg (36%) following trabeculectomy (P = 0.76). Although eyes treated with trabeculectomy required 1.1 fewer drops than phacoemulsification-treated eyes after surgery, they also had ten times the incidence of surgical complications (46% vs. 4%; P < 0.001).  Notably, 19% of patients from the phacoemulsification arm did eventually require trabeculectomy in the 2-year follow-up period. Though ultimately not as effective in terms of lowering IOP and reduced dependence on glaucoma medications as trabeculectomy in this study, phacoemulsification was still found to be an effective and safer option.
It is also noteworthy that the phacoemulsification arm of the Tham et al. study involved clear lenses rather than eyes with a visually disabling cataract. Until recently, there had been few randomized control trials evaluating clear lens extraction (CLE) in ACG and several reviews have criticized the role of CLE as being poorly substantiated by evidence. , Future studies evaluating CLE in addition to cataract extraction are further defining a bold frontier for phacoemulsification in ACG patients.
| Mechanisms of Iop Change|| |
The mechanism by which cataract surgery lowers IOP continues to be debated, but greater elucidation has been possible in recent years. In patients with CACG, outflow obstruction is a macroscopic problem-typically precipitated by mechanical blockage at the pupil or the angle. Thus, it seems safe to assume that removal of the lens would relieve the risk of pupillary block and posterior forces crowding the angle. Prior to cataract surgery, the mean anterior chamber angle width is approximately 10° less in ACG as compared to OAG and normal control eyes, and the anterior chamber depth is 1.0 mm shallower in the former relative to the latter groups (P < 0.0001). In ACG patients, the width and depth of the anterior chamber angle expand significantly following cataract extraction and IOL implantation, making the anatomy of ACG patients appear similar to those without this condition.  Huang et al. have also demonstrated a positive relationship between IOP reduction and preoperative lens vault measured by AS-optical coherence tomography (OCT). 
For POAG, however, where the site of the main resistance to aqueous drainage is thought to be microscopic blockage in the juxtacanalicular trabecular meshwork, it is less clear why cataract surgery is beneficial in lowering IOP. A number of mechanisms has been suggested, including reduction of glycosaminoglycan deposition in the trabecular meshwork due to higher fluid flow rates;  inflammation induced morphologic changes in the trabecular meshwork akin to the effects of laser trabeculoplasty;  remodeling of the trabecular endothelium secondary to ultrasonic vibrations;  and alterations in the blood-aqueous barrier.  Increased posterior zonular traction due to cataract surgery (whether due to lens removal alone or other technical aspects like small capsulorhexis) has been postulated to improve patency of the trabecular meshwork and result in lower IOP. ,,, Yang et al. studied a group of 999 patients and performed a battery of diagnostic tests including AS-OCT during the cataract surgery, optical biometry, and ultrasonic biomicroscopy. Measurements like changes in anterior chamber depth, angle opening distance, anterior chamber area, and lens thickness were better predictors of IOP change than was preoperative IOP.  These results suggest that changes in anterior chamber architecture may be just as important in effecting IOP change in POAG patients as in CACG patients.
| Cataract Surgery and The Diagnostic Management of Glaucoma|| |
Cataract extraction greatly enhances the practitioner's ability to diagnose and follow glaucomatous progression by improving visibility and has the added benefit of improved visual acuity for the patient. Fundoscopic examination of the optic nerve, OCT, and stereoscopic disc photos are more accurate after cataract removal. Kim et al. found that the presence of a cataract significantly affects measurements of both spectral domain-OCT (SD-OCT) and time domain-OCT (TD-OCT). Specifically, patients evaluated by SD-OCT were measured to have increased retinal nerve fiber layer thickness after cataract surgery as well as changes in signal strength values.  In addition, clinical perimetry is improved by more reliable patient performance and the elimination of lens-induced artifacts.
Rao et al. explored the reliability of visual fields in 53 POAG patients who underwent phacoemulsification or phacoemulsification combined with trabeculectomy. Preoperative and 15-month postoperative comparisons showed that mean deviation (MD) was significantly improved after surgery (postoperative −10.52 dB [range, −19.25 -−4.86 dB]) versus (preoperative −11.74 dB [range, −20.61 to −7.15 dB], P = 0.003). In eyes with MD better than − 20 dB, pattern standard deviation (PSD) worsened after surgery (postoperative 4.76 dB [range, 2.48-9.83]) versus (preoperative 3.50 dB [range, 1.93 - 8.20 dB], P = 0.01). Visual field index (VFI) remained unchanged (postoperative 80% vs. preoperative 77%; P = 0.92), leading the authors to conclude that VFI is the most reliable indicator of glaucomatous progression in patients with coexisting cataract and glaucoma.  Six years earlier, however, Siddiqui et al. had found converse results in a retrospective evaluation of 37 patients undergoing cataract extraction with or without trabeculectomy. Swedish interactive thresholding algorithm (SITA) PSD was stable (postoperative 7.3 ± 3.6 vs. preoperative 7.2 ± 3.0; P = 0.84) while MD improved (postoperative − 11.1 ± 6.3 vs. preoperative − 12.3 ± 5.8; P = 0.023). SITA-standard PSD was, therefore, suggested as the best metric for monitoring glaucomatous change.  Further studies may be needed to establish a robust perimetric measure or to classify how visual field results should be reinterpreted following cataract extraction. Regardless, the existing studies show that examiners should be wary of interpreting results depending on lens opacification and should re-establish diagnostic baselines after cataract surgery.
| Cataract Surgery and The Surgical Management of Glaucoma|| |
Beyond decreasing IOP and facilitating enhanced diagnostic monitoring of glaucoma, cataract surgery offers distinct surgical advantages when performed first in patients who will later require standard glaucoma-filtering surgery. Early cataract extraction avoids development of cataract-a common adverse effect of many glaucoma procedures. Within 5 years of trabeculectomy or tube shunt surgery, half of phakic patients develop a visually significant cataract. , As mentioned previously, 33% of eyes in the trabeculectomy arm of the Tham et al. study developed a cataract in the postoperative period - a complication that could have been precluded by phacoemulsification in the first place.  Among patients in the Collaborative Initial Glaucoma Treatment Study, who were randomized to initial surgical intervention, 20% ultimately required cataract extraction, with trabeculectomy noted to be the leading cause of cataract formation in this surgical group. 
The increasing frequency of performing cataract surgery prior to glaucoma-filtering surgery is a relatively recent phenomenon. The violation of the conjunctival space by superior extracapsular cataract extraction in a prior era made subsequent traditional glaucoma surgery more difficult. Phacoemulsification by temporal clear corneal incision, however, preserves the integrity of the conjunctiva for future glaucoma procedures. As discussed above, phacoemulsification expands the depth of the anterior chamber facilitating the performance of adjunctive or future ab interno angle glaucoma procedures. In addition, after trabeculectomy, pseudophakic eyes have less risk of lens-cornea touch, leading some to argue that iridectomy may no longer be a mandatory component of glaucoma-filtering surgery in pseudophakic patients.
While the technical advantages of cataract extraction before glaucoma-filtration surgery are readily apparent, some authors have questioned whether pseudophakic eyes are more likely to have failed trabeculectomy as compared to their phakic counterparts. A prospective cohort study of 39 phakic eyes and 25 pseudophakic eyes by Takihara et al. found that at 1-year after trabeculectomy, 95% of phakic eyes versus 74% pseudophakic eyes maintained IOP below 21 mmHg (P = 0.02), while 84% of phakic eyes versus 62% pseudophakic eyes maintained IOP below 18 mmHg (P = 0.04). However, there was no significant difference in the percentage of phakic versus pseudophakic eyes (67% vs. 53%, P = 0.10) that were able to maintain IOP below 15 mmHg. A similar study by Supawavej et al. compared 39 pseudophakic eyes to 39 phakic eyes undergoing trabeculectomy with MMC. At a median follow-up of 3 years, there was no significant difference between surgical success rates for IOP goals of (a) IOP ≤ 18 mmHg and ≥ 20% reduction of IOP, (b) IOP ≤ 15 mmHg and ≥ 25% reduction of IOP, and (c) IOP ≤ 12 mmHg and ≥ 30% reduction of IOP. The authors concluded that the clear-corneal phacoemulsification did not reduce the success of the subsequent initial trabeculectomy with MMC. 
The impetus for performing cataract surgery before glaucoma-filtration surgery is even greater when considering that a reverse order - glaucoma-filtration surgery before cataract surgery - may lead to poor outcomes particularly in terms of the trabeculectomy failure. Husain et al. studied 235 glaucoma participants who had undergone a single trabeculectomy augmented with either intraoperative 5-fluorouracil (5-FU) or placebo. One hundred and twenty-four (52.7%) of participants were judged to have significant lens opacity and underwent cataract surgery with intraocular lens placement at a median of 21.7 months after trabeculectomy. The sooner cataract surgery was performed after trabeculectomy, the higher the level of the trabeculectomy failure as defined by IOP > 21 mmHg. The hazard ratios for risk of subsequent trabeculectomy failure for cataract surgery performed at 6 months, 1-year and 2 years following trabeculectomy were 3.00 (95% confidence interval [CI], 1.11-8.14), 1.73 (95% CI, 1.05-2.85), and 1.32 (95% CI, 1.02-1.69), respectively.  In a retrospective analysis of 122 eyes with successful trabeculectomy surgery augmented by 5-FU, Salaga-Pylak similarly found that the 50 patients who underwent subsequent cataract extraction had approximately 20% lower success rate compared to patients that did not undergo cataract surgery at 6, 12, and 18 months postoperatively. Bleb morphology deteriorated in the cataract surgery group with reduction in both bleb size and elevation.  While the mechanisms of bleb failure in this context are not fully understood, phacoemulsification may lead to increased permeability of the blood-aqueous barrier, thereby facilitating the passage of inflammatory mediators that cause bleb fibrosis.
An "exception to the rule" of avoiding cataract surgery after filtering surgery is in patients with primary ACG. Unlike their counterparts with POAG, eyes with primary ACG may experience further IOP reduction when cataract surgery is performed after trabeculectomy. In a prospective interventional case series, Moghimi et al. performed phacoemulsification for visually significant cataracts in 37 eyes that had undergone trabeculectomy at least 12 months prior to study inclusion and found that IOP decreased significantly from 18.16 ± 5.91 mmHg at baseline to 15.37 ± 2.90 mmHg with 12 months follow-up (P < 0.01). The mean number of glaucoma medications decreased by approximately 1 (from 1.81 ± 0.24 at baseline to 0.86 ± 1.00; P = 0.001). This effect was most prominent in patients with higher preoperative IOP and shallow anterior chamber.  It is important to note these numbers reflect net effects. It is still possible that blebs are degraded by cataract surgery, but that ACG patients benefit so greatly from expansion of the anterior chamber, that there is still a cumulative benefit in terms of IOP lowering from cataract surgery following trabeculectomy.
Unlike the case with trabeculectomy surgery, cataract surgery following tube shunt surgery may improve vision without affecting IOP control.  Erie et al. performed a retrospective study of nine eyes following successful Baerveldt tube shunt for a mean of 21 months and found that visual acuity improved a mean of 4 ± 3 Snellen lines while IOP did not change significantly from baseline.  A number of other studies found similar results with both Baerveldt and Ahmed tube shunts. ,, However, in one study, some patients did require additional glaucoma medication for IOP elevation 1-month postoperatively.  In another study with small-incision cataract surgery, one eye out of 23 required a second Ahmed glaucoma valve.  Of note, all of these reports were retrospective case series with 23 or less eyes in each series. It would be interesting to see if these results are borne out in prospective randomized control trials.
| Combined Cataract and Glaucoma Procedures|| |
While stand-alone cataract surgery will decrease IOP, cataract surgery can also be performed in conjunction with MIGS procedures to enhance IOP reduction. The spectrum of nonpenetrating techniques, including canaloplasty, trabectome, iStent, can be primary surgical procedures but are often piggybacked on a cataract surgery. "Cataract plus" procedures are shifting the paradigm of glaucoma management by providing a safer option for patients who require additional IOP control, but are not good candidates for traditional filtration surgeries with their associated risks. Several MIGS procedures spare the conjunctiva thereby preventing compromise of future conjunctival-based glaucoma surgical procedures. As these new options become increasingly adopted, it is important to understand how they can be employed to augment IOP control.
In canaloplasty (iScience Interventional Corp., Menlo Park, CA), a nonpenetrating deep scleral flap is fashioned to allow viscodilation and 360° catheterization of Schlemm's canal by a flexible microcatheter. A suture is passed into the canal, which, when tied, distends Schlemm's canal by stretching the trabecular meshwork toward the anterior chamber. Combining canaloplasty with phacoemulsification can be technically challenging, but reportedly leads to significant IOP reduction. In a prospective multicenter study of 109 OAG patients who underwent canaloplasty or combined cataract-canaloplasty surgery, Bull et al. reported sustained decline in IOP for both arms, with a greater, albeit not statistically significant effect from the combined procedure than canaloplasty alone. Eyes receiving cataract-canaloplasty surgery went from a mean baseline IOP of 24.3 ± 6.0 mmHg to 13.8 ± 3.2 mmHg, while canaloplasty eyes went from a mean baseline IOP of 23.0 ± 4.3 mmHg to 15.1 ± 3.1 mmHg at 3 years postoperatively.  On average, patients in both groups required approximately one less glaucoma medication postoperatively. In a retrospective subset analysis of the same data, Tetz et al. analyzed the effects of canaloplasty in eyes that had previously undergone cataract surgery. Pseudophakic eyes receiving subsequent canaloplasty had similar results to surgery-naοve eyes undergoing combined cataract-canoloplasty, with mean baseline IOP dropping from 23.9 ± 5.2 mmHg to 15.6 ± 3.5 mmHg. 
Trabectome (Neomedix Inc., Tustin, CA) is a surgical device that can be used for ab interno trabeculotomy. Using electrocautery, the handpiece selectively ablates the trabecular meshwork and the inner wall of Schlemm's canal without damaging the outer wall of the canal. Francis et al. prospectively evaluated the effect of combined phaco-trabectome with promising results. Mean IOP decreased from 20.0 mmHg ± 6.3 preoperatively to 15.5 ± 2.9 mmHg at 1-year with patients requiring on average one less medication.  However, when comparing trabectome alone to phaco-trabectome, Minckler et al. found that mean preoperative IOP decreased by 40% (25.7 ± 7.7 mmHg to 16.6 ± 4.0 mmHg) versus 18% (20.0 ± 6.2 mmHg to 15.9 ± 3.3 mmHg) after 24 months, respectively.  Of note, the final IOP outcomes are quite similar between the groups. However, the preoperative IOP was significantly higher in the trabectome group, possibly contributing to the apparent disparity in IOP reduction. Both groups avoided serious complications. These results suggest phaco-trabectome may be a safe option for lowering IOP, but further studies are needed.
iStent (Glaukos Corp., Laguna Hills, CA) trabecular micro-bypass stent is a snorkel-shaped stent that is placed in the Schlemm's canal with an opening to the anterior chamber. Bypassing the trabecular meshwork, it is meant to provide a direct conduit for aqueous outflow. Samuelson et al. prospectively studied 240 eyes randomized to either phacoemulsification with iStent implantation or phacoemulsification alone. After 1-year, 72% of phaco-iStent eyes compared to 50% of phaco-only eyes achieved an unmedicated IOP ≤ 21 mmHg (P < 0.001). Significantly more phaco-iStent than phacoemulsication eyes achieved IOP reduction ≥ 20% (66% vs. 48%, P = 0.003).  At 2 years, data from the same iStent study group had a significantly greater portion of patients (approximately 80%) maintaining IOP ≤ 21 mmHg without medications.  Fea corroborated the superior efficacy of a combined procedure over phacoemulsification alone, showing approximately a 20% reduction in the combined group.  Recent reports on the placement of multiple iStents suggest that even greater IOP reductions can be achieved than with a single device. Belovay et al. demonstrated a mean postoperative IOP of 14.3 mmHg 1-year following phacoemulsification with 2-3 iStents. Multiple iStents may be advantageous by simply supplying a greater number of bypasses to the trabecular meshwork or by increasing the chances that any individual stent will lie near a collector channel. Further research is needed to establish the ideal number of iStents as well as the longevity of the IOP-lowering effect with this procedure. 
The above procedures are only a prelude to the potential impact that combined phacoemulsification and MIGS will have on glaucoma management. There are currently multiple promising MIGS devices under investigation, including the Hydrus microstent (Ivantis, Irvine, CA), CyPass microstent (Transcend Medical, Menlo Park, CA), AqueSys microfistula implant (AqueSys Inc., Aliso Viejo, CA) as well as several others.
| Conclusions|| |
From a public health perspective, cataract surgery is an incredibly cost-effective intervention for patients with glaucoma. It can be performed quickly with relatively little infrastructure, involves less postoperative care and is associated with fewer and less serious complications compared to more traditional glaucoma surgeries such as trabeculectomy and tube shunt surgery. Cataract surgery has been shown on average to decrease the postoperative dependence on glaucoma medications. All of these reasons make cataract surgery an especially appealing option for long-term glaucoma management in underserved areas where access to glaucoma subspecialty care is limited.
In the glaucoma specialist's race against time, a simple cataract surgery may buy several years of IOP control and delay the morbidity of traditional filtering surgeries. In spite of the medical and economic advantages of cataract surgery for glaucoma management, many ophthalmologists are hesitant to perform early extraction in patients whose cataracts do not yet limit their activities of daily living. In the light of the above discussion, perhaps it is time to rethink the conventional indications for cataract surgery. A "glaucomatous cataract" is no longer limited to the categories of phacolytic, phacoanaphylactic, or phacomorphic glaucomatous disease, but rather should be a consideration in any glaucoma patient who could benefit from a sustained decrease in IOP from cataract removal and has some degree of visual disability from cataract.
| References|| |
Khairallah M, Kahloun R, Flaxman SR, Jonas JB, Keeffe J, Leasher J, et al.
Prevalence and causes of vision loss in North Africa and the Middle East: 1990-2010. Br J Ophthalmol 2014;98:605-11.
Resnikoff S, Pascolini D, Etya'ale D, Kocur I, Pararajasegaram R, Pokharel GP, et al.
Global data on visual impairment in the year 2002. Bull World Health Organ 2004;82:844-51.
Quigley HA, Broman AT. The number of people with glaucoma worldwide in 2010 and 2020. Br J Ophthalmol 2006;90:262-7.
Poley BJ, Lindstrom RL, Samuelson TW, Schulze R Jr. Intraocular pressure reduction after phacoemulsification with intraocular lens implantation in glaucomatous and nonglaucomatous eyes: Evaluation of a causal relationship between the natural lens and open-angle glaucoma. J Cataract Refract Surg 2009;35:1946-55.
Shingleton BJ, Laul A, Nagao K, Wolff B, O'Donoghue M, Eagan E, et al.
Effect of phacoemulsification on intraocular pressure in eyes with pseudoexfoliation: Single-surgeon series. J Cataract Refract Surg 2008;34:1834-41.
Friedman DS, Jampel HD, Lubomski LH, Kempen JH, Quigley H, Congdon N, et al.
Surgical strategies for coexisting glaucoma and cataract: An evidence-based update. Ophthalmology 2002;109:1902-13.
Bigger JF, Becker B. Cataracts and primary open-angle glaucoma: The effect of uncomplicated cataract extraction on glaucoma control. Trans Am Acad Ophthalmol Otolaryngol 1971;75:260-72.
Matsumura M, Mizoguchi T, Kuroda S, Terauchi H, Nagata M. Intraocular pressure decrease after phacoemulsification-aspiration intraocular lens implantation in primary open angle glaucoma eyes. Nihon Ganka Gakkai Zasshi 1996;100:885-9.
Shingleton BJ, Pasternack JJ, Hung JW, O'Donoghue MW. Three and five year changes in intraocular pressures after clear corneal phacoemulsification in open angle glaucoma patients, glaucoma suspects, and normal patients. J Glaucoma 2006;15:494-8.
Mansberger SL, Gordon MO, Jampel H, Bhorade A, Brandt JD, Wilson B, et al.
Reduction in intraocular pressure after cataract extraction: The Ocular Hypertension Treatment Study. Ophthalmology 2012;119:1826-31.
Ritch R, Schlötzer-Schrehardt U. Exfoliation syndrome. Surv Ophthalmol 2001;45:265-315.
Ritch R. Exfoliation syndrome and occludable angles. Trans Am Ophthalmol Soc 1994;92:845-944.
Olawoye OO, Ashaye AO, Teng CC, Liebmann JM, Ritch R, Ajayi BG. Exfoliation syndrome in Nigeria. Middle East Afr J Ophthalmol 2012;19:402-5.
Shingleton BJ, Crandall AS, Ahmed II. Pseudoexfoliation and the cataract surgeon: Preoperative, intraoperative, and postoperative issues related to intraocular pressure, cataract, and intraocular lenses. J Cataract Refract Surg 2009;35:1101-20.
Naumann GO. Exfoliation syndrome as a risk factor for vitreous loss in extracapsular cataract surgery (preliminary report). Erlanger-Augenblätter-Group. Acta Ophthalmol Suppl 1988;184:129-31.
Åström S, Stenlund H, Lindén C. Intraocular pressure changes over 21 years-a longitudinal age-cohort study in northern Sweden. Acta Ophthalmol 2014;92:417-20.
Hayashi K, Hayashi H, Nakao F, Hayashi F. Effect of cataract surgery on intraocular pressure control in glaucoma patients. J Cataract Refract Surg 2001;27:1779-86.
Shams PN, Foster PJ. Clinical outcomes after lens extraction for visually significant cataract in eyes with primary angle closure. J Glaucoma 2012;21:545-50.
Husain R, Gazzard G, Aung T, Chen Y, Padmanabhan V, Oen FT, et al.
Initial management of acute primary angle closure: A randomized trial comparing phacoemulsification with laser peripheral iridotomy. Ophthalmology 2012;119:2274-81.
Tham CC, Kwong YY, Baig N, Leung DY, Li FC, Lam DS. Phacoemulsification versus trabeculectomy in medically uncontrolled chronic angle-closure glaucoma without cataract. Ophthalmology 2013;120:62-7.
Friedman DS, Vedula SS. Lens extraction for chronic angle-closure glaucoma. Cochrane Database Syst Rev 2006;CD005555.
Thomas R, Walland MJ, Parikh RS. Clear lens extraction in angle closure glaucoma. Curr Opin Ophthalmol 2011;22:110-4.
Hayashi K, Hayashi H, Nakao F, Hayashi F. Changes in anterior chamber angle width and depth after intraocular lens implantation in eyes with glaucoma. Ophthalmology 2000;107:698-703.
Huang G, Gonzalez E, Lee R, Chen YC, He M, Lin SC. Association of biometric factors with anterior chamber angle widening and intraocular pressure reduction after uneventful phacoemulsification for cataract. J Cataract Refract Surg 2012;38:108-16.
Kim DD, Doyle JW, Smith MF. Intraocular pressure reduction following phacoemulsification cataract extraction with posterior chamber lens implantation in glaucoma patients. Ophthalmic Surg Lasers 1999;30:37-40.
Tong JT, Miller KM. Intraocular pressure change after sutureless phacoemulsification and foldable posterior chamber lens implantation. J Cataract Refract Surg 1998;24:256-62.
Wang N, Chintala SK, Fini ME, Schuman JS. Ultrasound activates the TM ELAM-1/IL-1/NF-kappaB response: A potential mechanism for intraocular pressure reduction after phacoemulsification. Invest Ophthalmol Vis Sci 2003;44:1977-81.
Miyake K, Asakura M, Kobayashi H. Effect of intraocular lens fixation on the blood-aqueous barrier. Am J Ophthalmol 1984;98:451-5.
Kooner KS, Cooksey JC, Perry P, Zimmerman TJ. Intraocular pressure following ECCE, phacoemulsification, and PC-IOL implantation. Ophthalmic Surg 1988;19:643-6.
Kooner KS, Dulaney DD, Zimmerman TJ. Intraocular pressure following extracapsular cataract extraction and posterior chamber intraocular lens implantation. Ophthalmic Surg 1988;19:471-4.
Johnstone MA. The aqueous outflow system as a mechanical pump: Evidence from examination of tissue and aqueous movement in human and non-human primates. J Glaucoma 2004;13:421-38.
Cekiç O, Batman C. Effect of capsulorhexis size on postoperative intraocular pressure. J Cataract Refract Surg 1999;25:416-9.
Yang HS, Lee J, Choi S. Ocular biometric parameters associated with intraocular pressure reduction after cataract surgery in normal eyes. Am J Ophthalmol 2013;156:89-94.e1.
Kim NR, Lee H, Lee ES, Kim JH, Hong S, Je Seong G, et al.
Influence of cataract on time domain and spectral domain optical coherence tomography retinal nerve fiber layer measurements. J Glaucoma 2012;21:116-22.
Rao HL, Jonnadula GB, Addepalli UK, Senthil S, Garudadri CS. Effect of cataract extraction on Visual Field Index in glaucoma. J Glaucoma 2013;22:164-8.
Rehman Siddiqui MA, Khairy HA, Azuara-Blanco A. Effect of cataract extraction on SITA perimetry in patients with glaucoma. J Glaucoma 2007;16:205-8.
Jampel HD, Solus JF, Tracey PA, Gilbert DL, Loyd TL, Jefferys JL, et al.
Outcomes and bleb-related complications of trabeculectomy. Ophthalmology 2012;119:712-22.
Gedde SJ, Herndon LW, Brandt JD, Budenz DL, Feuer WJ, Schiffman JC, et al.
Postoperative complications in the Tube Versus Trabeculectomy (TVT) study during five years of follow-up. Am J Ophthalmol 2012;153:804-14.e1.
Zahid S, Musch DC, Niziol LM, Lichter PR, Collaborative Initial Glaucoma Treatment Study Group. Risk of endophthalmitis and other long-term complications of trabeculectomy in the Collaborative Initial Glaucoma Treatment Study (CIGTS). Am J Ophthalmol 2013;155:674-680, e1.
Supawavej C, Nouri-Mahdavi K, Law SK, Caprioli J. Comparison of results of initial trabeculectomy with mitomycin C after prior clear-corneal phacoemulsification to outcomes in phakic eyes. J Glaucoma 2013;22:52-9.
Husain R, Liang S, Foster PJ, Gazzard G, Bunce C, Chew PT, et al.
Cataract surgery after trabeculectomy: The effect on trabeculectomy function. Arch Ophthalmol 2012;130:165-70.
Salaga-Pylak M, Kowal M, Zarnowski T. Deterioration of filtering bleb morphology and function after phacoemulsification. BMC Ophthalmol 2013;13:17.
Moghimi S, Latifi G, Amini H, Mohammadi M, Fakhraie G, Eslami Y, et al.
Cataract surgery in eyes with filtered primary angle closure glaucoma. J Ophthalmic Vis Res 2013;8:32-8.
Patel HY, Danesh-Meyer HV. Incidence and management of cataract after glaucoma surgery. Curr Opin Ophthalmol 2013;24:15-20.
Erie JC, Baratz KH, Mahr MA, Johnson DH. Phacoemulsification in patients with Baerveldt tube shunts. J Cataract Refract Surg 2006;32:1489-91.
Bhattacharyya CA, WuDunn D, Lakhani V, Hoop J, Cantor LB. Cataract surgery after tube shunts. J Glaucoma 2000;9:453-7.
Sa HS, Kee C. Effect of temporal clear corneal phacoemulsification on intraocular pressure in eyes with prior Ahmed glaucoma valve insertion. J Cataract Refract Surg 2006;32:1011-4.
Gujral S, Nouri-Mahdavi K, Caprioli J. Outcomes of small-incision cataract surgery in eyes with preexisting Ahmed Glaucoma Valves. Am J Ophthalmol 2005;140:911-3.
Bull H, von Wolff K, Körber N, Tetz M. Three-year canaloplasty outcomes for the treatment of open-angle glaucoma: European study results. Graefes Arch Clin Exp Ophthalmol 2011;249:1537-45.
Tetz M, Koerber N, Shingleton BJ, von Wolff K, Bull H, Samuelson TW, et al.
Phacoemulsification and intraocular lens implantation before, during, or after canaloplasty in eyes with open-angle glaucoma: 3-Year Results. J Glaucoma 2013.
Francis BA, Minckler D, Dustin L, Kawji S, Yeh J, Sit A, et al.
Combined cataract extraction and trabeculotomy by the internal approach for coexisting cataract and open-angle glaucoma: Initial results. J Cataract Refract Surg 2008;34:1096-103.
Minckler D, Mosaed S, Dustin L, Ms BF, Trabectome Study Group. Trabectome (trabeculectomy-internal approach): Additional experience and extended follow-up. Trans Am Ophthalmol Soc 2008;106:149-59.
Samuelson TW, 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;118:459-67.
Craven ER, Katz LJ, Wells JM, Giamporcaro JE, iStent Study Group. Cataract surgery with trabecular micro-bypass stent implantation in patients with mild-to-moderate open-angle glaucoma and cataract: Two-year follow-up. J Cataract Refract Surg 2012;38:1339-45.
Fea AM. Phacoemulsification versus phacoemulsification with micro-bypass stent implantation in primary open-angle glaucoma: Randomized double-masked clinical trial. J Cataract Refract Surg 2010;36:407-12.
Belovay GW, Naqi A, Chan BJ, Rateb M, Ahmed II. Using multiple trabecular micro-bypass stents in cataract patients to treat open-angle glaucoma. J Cataract Refract Surg 2012;38:1911-7.