Comparison of long-term incidence of posterior capsular opacification between phacoemulsification and phacotrabeculectomy

Comparison of Long-term Incidence of Posterior Capsular Opacification Between Phacoemulsification and Phacotrabeculectomy DONG H. SHIN, MD, PHD, SCOTT M. VANDENBELT, MD, PAUL H. KIM, BA, JASON P. GROSS, MD, NANDITA S. KEOLE, MD, SANG H. LEE, MD, CATHERINE M. BIRT, MD, FRCSC, AND STEVEN Y. REED, MD

● PURPOSE:

To investigate the long-term incidence of posterior capsular opacification after phacoemulsification compared with phacotrabeculectomy with or without adjunctive subconjunctival mitomycin C. ● METHODS: This was a retrospectively conducted longterm, observational, case-control study. One hundred eyes of 100 cataract patients who underwent phacoemulsification and posterior chamber intraocular lens implantation and 100 eyes of 100 primary open-angle glaucoma patients with cataract that underwent phacotrabeculectomy and posterior chamber intraocular lens implantation, matched with respect to age, intraocular lens type, prevalence of diabetes mellitus, and length of follow-up. The main outcome measure was the rate of clinically significant posterior capsular opacification as determined by slit-lamp biomicroscopy and necessity to perform neodynium:yttrium aluminum garnet (Nd:YAG) capsulotomy and as calculated by Kaplan-Meier survival analysis. Postoperative visual acuity and maintenance of intraocular pressure control were also measured. ● RESULTS: There was no significant difference in the rate of posterior capsular opacification requiring Nd: YAG capsulotomy between the phacoemulsification and phacotrabeculectomy groups (P ⴝ .77). However, a significant difference in the rate of posterior capsular opacification was found between those patients without diabetes mellitus and those with a preoperative diagnosis Accepted for publication Sep 7, 2001. From the Kresge Eye Institute, Wayne State University School of Medicine (D.H.S., S.M.V., P.H.K., J.P.G., N.S.K., S.Y.R.), Detroit, Michigan; Pusan National University College of Medicine (S.H.L.), Pusan, Korea; Sunnybrook Health Science Centre, University of Toronto (C.M.B.), Toronto, Ontario, Canada. The content of this study was presented in part as a poster at the 2001 annual meeting of the Association for Research in Vision and Ophthalmology, Fort Lauderdale, Florida. This study was supported, in part, by an unrestricted grant from Research to Prevent Blindness, Inc, New York, New York. Reprint requests to Dong H. Shin, MD, PhD, Kresge Eye Institute and Wayne State University School of Medicine, 4717 St Antoine Boulevard, Detroit, MI 48201-1423; fax: (313) 577-4991; e-mail: dongshin@ med.wayne.edu

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of diabetes mellitus (P ⴝ .016). Also, survival analysis comparing use of mitomycin C with no use of mitomycin C in the phacotrabeculectomy group showed a higher survival in the mitomycin C subgroup (P ⴝ .03). ● CONCLUSION: There was no significant difference in long-term posterior capsular opacification between phacoemulsification and phacotrabeculectomy in the study population. Intraoperative, adjunctive use of mitomycin C in the phacotrabeculectomy group and the presence of diabetes mellitus in the overall patients were beneficial (protective) factors against posterior capsular opacification. (Am J Ophthalmol 2002;133:40 – 47. © 2002 by Elsevier Science Inc. All rights reserved.)

A

DVANCES IN SURGICAL TECHNIQUE AND INTRAOC-

ular lens have decreased posterior capsular opacification after phacoemulsification with posterior chamber intraocular implant. However, posterior capsular opacification remains a major complication of cataract surgery.1–17 Previously, we examined the effects of mitomycin C on posterior capsular opacification in primary glaucoma triple procedure. It was revealed that the rate of posterior capsular opacification decreased with use of adjunctive mitomycin C.18 Whereas the rate of posterior capsular opacification is expected to be higher in patients with glaucoma undergoing combined surgery than nonglaucomatous patients undergoing straight cataract surgery, there has not been a study comparing the rate of posterior capsular opacification between the two groups of patients. Therefore, we conducted the present comparative study of posterior capsular opacification between phacoemulsification and phacotrabeculectomy with posterior chamber intraocular lens implantation.

PATIENTS AND METHODS THIS STUDY REPRESENTS A LONG-TERM, OBSERVATIONAL,

case-control study. In this retrospective, case review study,

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877 consecutive phacoemulsification or phacotrabeculectomy (200 phacoemulsification, 677 phacotrabeculectomy) cases were reviewed. Patient demographics, including age, sex, race, diabetes mellitus, hypertension, and previous ocular surgeries, were recorded for all patients. Additionally, preoperative intraocular pressure, preoperative visual acuity, preoperative ocular medication number and type, cataract surgical procedure (phacoemulsification vs phacotrabeculectomy), intraocular lens type (polymethylmethacrylate, silicone, or acrylic), cup-to-disk ratio, Humphrey visual field data, and mitomycin C for phacotrabeculectomy cases were recorded. At 1, 2, 3, 6, 9, 12, 15, 18, 21, 24, 30, 36, 42, and 48 months postoperatively, patients were examined for intraocular pressure, number of medications for intraocular pressure control, and the best-corrected visual acuity. Presence of clinically significant posterior capsular opacification was determined by clinical findings using slit-lamp biomicroscopy (2⫹ or greater in the scale of 0 to 3⫹) and receipt of neodynium:yttrium aluminum garnet (Nd:YAG) laser capsulotomy, the primary purpose of which was improvement of visual acuity. A secondary benefit of obtaining a clearer view of the fundus was also taken into consideration in case there may have been a cause of decrease of visual acuity other than posterior capsular opacification, as well as easier evaluation of the status of the fundus in subsequent examinations. Time of Nd:YAG capsulotomy from initial procedure was also recorded. Lastly, significant postoperative complications and additional ocular procedures were recorded for each patient. Eyes with previous penetrating ocular surgery (n ⫽ 79), inadequate preoperative data (n ⫽ 24), and patients with follow-up less than 30 months (n ⫽ 118) were excluded. Random elimination of one eye was done if the patient had bilateral surgery (n ⫽ 159). The exclusions left 100 eyes of 100 phacoemulsification patients and 397 eyes of 397 phacotrabeculectomy patients. None of the phacoemulsification eyes had preoperative glaucoma or ocular hypertension, nor was any of them on ocular hypertensive medication. Patients of the two groups were then matched, phacoemulsification (n ⫽ 100) and phacotrabeculectomy (n ⫽ 100), with regard to preoperative diagnosis of diabetes mellitus, intraocular lens (polymethylmethacrylate, acrylic, or silicone), age, and length of follow-up. Because the number of the phacotrabeculectomy eyes was four times that of the phacoemulsification eyes, the phacotrabeculectomy eyes were matched to the phacoemulsification eyes by necessity. In case there was more than one phacotrabeculectomy eye that qualified for matching, the eye that matched most closely with respect to and in the order of the type of intraocular lens, the length of follow-up, diabetes mellitus, and hypertension, age, race, and sex was chosen to be included in our study. Because mitomycin C was not used in any of the phacoemulsification eyes, but only in the phacotrabeculectomy eyes on a random basis, it was not taken into consideration during the matching process. In fact, the person involved in the matching, as well as the examiners, VOL. 133, NO. 1

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was masked with respect to mitomycin C use in the phacotrabeculectomy eyes. Each surgery was performed by the same surgeon (Dr Shin), using the same technique. Patients were first prepped and draped, local anesthesia was achieved with modified Van Lint and retrobulbar blocks, and injections of 40 mg each of subconjunctival gentamicin and subtenon’s triamcinolone were then given. For each phacoemulsification procedure, paracentesis and an incision into the anterior chamber of approximately 3.5 mm followed by capsulorhexis, hydrodissection, phacoemulsification, and thorough instrumental lens cortex removal was carried out using an irrigation-aspiration probe until there remained no visible cortical material in the posterior chamber, including the anterior surface of the posterior capsule. Very rarely, we resorted to the use of a capsule polisher for cortical plaque that resisted this maneuver. The capsular bag was inflated with sodium hyaluronate, and the fullthickness corneoscleral incision was enlarged to approximately 5 mm for insertion of a polymethylmethacrylate lens for those cases in which a polymethylmethacrylate lens was used. After insertion of a polymethylmethacrylate, silicone, or acrylic lens, the remaining viscoelastic material was removed using the irrigation–aspiration probe after the corneoscleral wound was partially closed using an interrupted 9-0 nylon suture, and the intraocular lens was rotated with its long axis in the horizontal meridian.19 For the phacotrabeculectomy, a 7-mm (chord length) fornixbased conjunctival flap, including the Tenon capsule, was made to expose bare sclera in the superior quadrant. An episcleral traction suture was placed 7 mm posterior to the limbus. Then a limbus-based, triangular, half-thickness, lamellar-scleral flap was dissected measuring 3 mm at the base and 3 mm to the apex from each corner, and extended on either side for later enlargement of the corneoscleral wound for insertion of an intraocular lens. At this point in the mitomycin C group, a small piece of cellulose sponge soaked in 0.5 mg/ml solution of mitomycin C, with a hydrated dimension of approximately 2 ⫻ 3 ⫻ 7 mm, was placed under the conjunctival flap over the dissected scleral flap. After the cellulose sponge was removed, the conjunctival flap was everted and the space between the flap and the episclera was irrigated with copious quantities of balanced salt solution and inspected to ensure absence of sponge remnants. A paracentesis and an incision into the anterior chamber of approximately 3.5 mm was made, and capsulorhexis, hydrodissection, phacoemulsification and cortical clean-up followed. The capsular bag was inflated with sodium hyaluronate and the full-thickness, corneoscleral incision was enlarged to approximately 5 mm to accommodate a polymethylmethacrylate lens for those cases in which a polymethylmethacrylate intraocular lens was used. After insertion of a polymethylmethacrylate, silicone, or acrylic lens, the intraocular lens was rotated with its long axis in the horizontal meridian. A trabeculectomy opening was made under the scleral flap using a OF

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TABLE 1. Preoperative Patient Characteristics PE (n ⫽ 100)

Characteristic

Age (mean⫾ SD, years) Race African American Caucasian Sex Male Female Hypertension (%) Diabetes (%) Lens material PMMA Silicone Acrylic Mean follow-up (months) Cup-to-disk ratio (mean ⫾ SD) Preoperative IOP (mean ⫾ SD, mm Hg) Preoperative medication number (mean ⫾ SD) MMC use (%)

PT (n ⫽ 100)

P Value

72.3 ⫾ 9.2

72.4 ⫾ 8.9

58 42

58 42

⬎.99†

37 63 46 (46%) 23 (23%)

37 63 37 (37%) 23 (23%)

⬎.99†

60 24 16 64.3 ⫾ 26.9 0.49 ⫾ 0.20 16.1 ⫾ 3.7 — 0 (0%)

60 24 16 56.2 ⫾ 19.0 0.80 ⫾ 0.14 20.1 ⫾ 7.9 2.3 ⫾ 1.1 70 (70%)

⬎.99†

.95*

.28* ⬎.99*

.014* ⬍.0001* ⬍.0001* ⬍.0001* ⬍.0001†

IOP ⫽ intraocular pressure; MMC ⫽ mitomycin C; PE ⫽ phacoemulsification; PMMA ⫽ polymethylmethacrylate; PT ⫽ phacotrabeculectomy. *Unpaired student t test. † Chi-square test.

Gass punch, followed by peripheral iridectomy using Vannas scissors. The remaining viscoelastic material was removed by irrigation–aspiration. The triangular scleral flap was closed with one apical, releasable 9-0 nylon suture, as described previously.20 –22 The scleral flap closure was adjusted to be tight enough to allow full inflation of the anterior chamber but not too tight to prevent egress of a small amount of fluid when balanced salt solution was injected through the paracentesis track. The conjunctival flap was sutured to the corneoscleral limbus with a maximal stretch using 9-0 nylon suture. The resultant conjunctival dog-ear-like defect also was closed for a watertight closure using a running 9-0 nylon suture. Balanced salt solution was injected into the anterior chamber to ascertain conjunctival bleb formation and absence of wound leakage.23 Postoperatively, the phacoemulsification patients were started with corticosteroid–antibiotic ointment at bedtime and prednisolone acetate 1% drops four times daily, which were gradually tapered, usually over a period of 1 month. The phacotrabeculectomy patients received a more vigorous corticosteroid routine postoperatively, with corticosteroid–antibiotic ointment at bedtime and prednisolone acetate 1% drops every hour while awake, which were gradually tapered over several weeks, depending on the postoperative state of the operated eye. The data were analyzed using Statview version 5.0 by SAS Institute, Inc (Cary, North Carolina). 42

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RESULTS TABLE 1 CONFIRMS THAT THE PHACOEMULSIFICATION AND

phacotrabeculectomy groups are indeed closely matched per our study design in age, prevalence of diabetes mellitus, the length of follow-up, and intraocular lens. The two groups also did not differ significantly with regard to race, sex, and prevalence of hypertension (Table 1). As expected, there were significant differences between the two groups in C:D ratio (P ⬍ .0001), preoperative intraocular pressure (P ⬍ .0001), preoperative medication number (P ⬍ .0001), and mitomycin C use (P ⬍ .0001). Mitomycin C was used only in phacotrabeculectomy and therefore showed significant predilection for the phacotrabeculectomy group. Mean intraocular pressure remained relatively stable in the phacoemulsification group over the 48-month follow-up, ranging from 16.1 ⫾ 3.7 mm Hg to 15.4 ⫾ 3.6 mm Hg (P ⫽ .37, repeated measures analysis of variance). Mean intraocular pressure in the phacotrabeculectomy group initially decreased significantly from a preoperative mean intraocular pressure of 19.7 ⫾ 7.2 to 15.3 ⫾ 6.5 mm Hg at 1 month (P ⫽ .0001) and then stabilized between 14.1 ⫾ 4.4 and 15.6 ⫾ 6.0 mm Hg during the period from 6 months to 48 months of follow-up (P ⫽ .0001, repeated measures analysis of variance; Figure 1). Also, the number of medications in the phacotrabeculectomy group decreased significantly from its preoperative mean value of OF

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FIGURE 1. Mean intraocular pressure in mm Hg for phacoemulsification group (PE, open circle) vs phacotrabeculectomy group (PT, filled circle). The standard errors of the mean are represented by the vertical bars.

FIGURE 2. Kaplan-Meier cumulative survival plot for probability of postoperative posterior capsular opacification requiring Nd:YAG laser capsulotomy of phacoemulsification group (PE, open circle) vs phacotrabeculotomy group (PT, filled circle) group.

2.3 ⫾ 1.1 to its postoperative mean value of 1.4 ⫾ 1.3 at 48 months of follow-up (P ⫽ .0001). No significant difference was found in survival time, with an end point of Nd:YAG capsulotomy for posterior capsular opacification, between the two matched groups (P ⫽ .77 by Kaplan-Meier survival analysis with MantelCox log-rank test; Figure 2). A significant difference in posterior capsular opacification rate was found, however, between the phacotrabeculectomy subgroups with (n ⫽ VOL. 133, NO. 1

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70) and without (n ⫽ 30) mitomycin C use (P ⫽ .03 by Kaplan-Meier survival plots with Mantel-Cox log-rank test; Figure 3). The survival time was also found to be significantly increased (P ⫽ .017) in the presence of diabetes mellitus (Figure 4). Survival time was not significantly affected by the lens material type (polymethylmethacrylate, acrylic, or silicone) in either the phacoemulsification (P ⫽ .72) or phacotrabeculectomy (P ⫽ .46) group (Table 2). Lastly, visual acuity with best correction was found to OF

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FIGURE 3. Probability of postoperative posterior capsular opacification requiring Nd: YAG laser capsulotomy in the phacotrabeculectomy subgroups without mitomycin C use (open circle, n ⴝ 30) vs with mitomycin C use (MMC, filled circle, n ⴝ 70) (P ⴝ .03).

FIGURE 4. Kaplan-Meier cumulative survival (time in months) plot for patients with a preoperative diagnosis of diabetes mellitus (DM, filled circle, n ⴝ 46) vs patients without a diagnosis of diabetes (open circle, n ⴝ 154). Mantel-Cox log-rank test of above data showed diabetes as a protective factor against posterior capsular opacification regarding Nd:YAG capsulotomy (P ⴝ .016).

have stabilized at 6 months postoperatively after phacoemulsification and remained stable through 4 years of follow-up (Figure 5). Visual acuity was also stable by approximately 6 months after phacotrabeculectomy as well, but decreased slightly in the later months of the study (later than 30 months). The fact that visual acuity stayed stable beyond the postoperative 6 months is indirect 44

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evidence of the beneficial effect of the Nd:YAG capsulotomy in the eyes with posterior capsular opacification. If Nd:YAG capsulotomy had not been performed in the eyes with posterior capsular opacification or if the eyes with posterior capsular opacification had not benefited from the Nd:YAG capsulotomy, there would have been a gradual decrease of mean visual acuity, with time, in both groups. OF

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TABLE 2. Postoperative Outcome Measures by Lens Type

Characteristic

PE Number Nd:YAG capsulotomy Mean Nd:YAG time (months) ⫾ SEM PT Number Nd:YAG capsulotomy Mean Nd:YAG time (months) ⫾ SEM

PMMA (n ⫽ 60)

Acrylic (n ⫽ 16)

Silicone (n ⫽ 24)

P Value

18 (30%) 62.2 ⫾ 3.1

4 (25%) 45.2 ⫾ 4.4

8 (33%) 31.1 ⫾ 2.8

.79*

20 (33%) 62.6 ⫾ 3.4

2 (13%) 29.1 ⫾ 2.4

7 (29%) 37.1 ⫾ 2.8

.46*

Nd:YAG ⫽ neodynium:yttrium aluminum garnet; PE ⫽ phacoemulsification; PMMA ⫽ polymethylmethacrylate; PT ⫽ phacotrabeculectomy; SEM ⫽ standard error of the mean. *Mantel-Cox log-rank test.

FIGURE 5. Mean decimal visual acuity (ⴞ standard error) of the mean for each period of follow-up (time in months) for phacoemulsification (PE, open circle) and phacotrabeculectomy (PT, filled circle).

The very slight decrease of the mean visual acuity during the latter part of the phacotrabeculectomy group may reflect one or more possibilities: further optic nerve damage might have occurred in some eyes because of fluctuation of intraocular pressure, despite attainment of mean target intraocular pressure control, or further optic nerve damage might have taken place, albeit rare, despite very low intraocular pressure short of hypotony. A post hoc statistical power analysis revealed that the study powers of survival comparisons with log-rank test were 97.6%, 78.1%, and 95.5% between the phacoemulsification and phacotrabeculectomy groups, between the phacotrabeculectomy subgroups with and without mitomycin C use, and between the groups with and without diabetes mellitus, respectively. The sample size of the intraocular lens subgroups was too small for meaningful power calculation of the subgroup comparisons. VOL. 133, NO. 1

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DISCUSSION THERE WAS NO SIGNIFICANT DIFFERENCE IN THE INCI-

dence of posterior capsular opacification between the phacoemulsification and phacotrabeculectomy groups (Figure 2). It is surprising that the phacotrabeculectomy group did not develop a significantly higher incidence of posterior capsular opacification than the phacoemulsification group. All of the phacotrabeculectomy patients were on antiglaucoma medications, some of which are known to cause breakdown of blood aqueous barrier and thus promote or prolong intraocular inflammation. Many of the phacotrabeculectomy patients had a bound down or poorly dilatable pupil that often required a mechanical manipulation such as stretching or sphincterotomies, which in turn would have contributed to intraocular inflammation as well as hemorrhage. Conversely, the phacotrabeculecOF

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tomy patients had a much more vigorous corticosteroid therapeutic routine postoperatively, and a great majority of them also had intraoperative mitomycin C. Both the intensive postoperative corticosteroid and intraoperative mitomycin C, which were used to improve the filtration outcome of phacotrabeculectomy, were probably beneficial in suppressing the intraocular inflammation and/or inhibiting the lens epithelial cell proliferation. In fact, this study supports the previous observation that mitomycin C is protective against posterior capsular opacification.18 It is appropriate to point out that measurable concentrations of mitomycin C have been observed in the aqueous and the vitreous after adjunctive, intraoperative applications of mitomycin C during the glaucoma filtration surgery.24 –27 Of great interest, visually significant posterior capsular opacification also occurred significantly less often in those patients having a preoperative diagnosis of diabetes mellitus than in those without the diagnosis (P ⫽ .017). These data concur with a previous observation that diabetes mellitus is a negative risk factor for, or is protective against, posterior capsular opacification18,28 but differs from another study that reported no overall difference in posterior capsular opacification rates between diabetics in general and nondiabetics.29 One proposed mechanism of pathogenesis of posterior capsular opacification is lens epithelial cell proliferation and migration from the equatorial and anterior subcapsular epithelium.1,18 This proliferation and migration can be thought of as a healing reaction initiated by remaining postsurgical lens epithelial cells. Mitomycin C is a potent antiproliferative agent, and it needs to be underscored again that measurable concentrations of mitomycin C have been demonstrated in the aqueous and vitreous after usual intraoperative application in glaucoma filtration surgery.24 –27 Diabetes mellitus is also a known risk factor for decreased wound healing. Knorz and associates28 hypothesized that accumulation of sorbitol and fructose in the lens epithelial cells results in reduced proliferation of the cells. Therefore, the decreased incidences of posterior capsular opacification in patients with diabetes and also in the phacotrabeculectomy patients with mitomycin C use could be attributed to the decrease in the healing response related to diabetes mellitus and with mitomycin C use, respectively.18,28 The intraocular lens material did not seem to have a significant effect on posterior capsular opacification in either phacoemulsification or phacotrabeculectomy patients in our study (Table 2). This is in contrast with other studies that show significant differences in posterior capsular opacification rate depending on the lens material used.1,5,15,17,30 –32 Hollick and associates5 found that 2 years after phacoemulsification with posterior chamber intraocular lens insertion, all polymethylmethacrylate and silicone lenses had lens epithelial cell proliferation or posterior capsular opacification, whereas 63% of polyacrylic lenses had undergone these changes. Again, vigorous intraoperative and postoperative uses of corticosteroids, 46

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especially in the phacotrabeculectomy group, and also the intraoperative use of mitomycin C in the great majority of the phacotrabeculectomy group in our study may be, at least in part, responsible for the difference. Furthermore, the results of a recent prospective study with randomization were consistent with our present study findings.14 In that study, comparing the long-term incidence of posterior capsular opacification between silicone and acrylic intraocular lenses after phacotrabeculectomy in patients with glaucoma, there was no significant difference. It is appropriate to point out, however, that our study, as well as the other studies, has the usual shortcomings of a retrospective study without randomization. Additionally, in the present study, albeit a properly designed, case-controlled long-term study with rigorous matching of relevant variables between the two study groups and a fair sample size (100 each group) for group comparisons, the sample sizes of the three intraocular lens subgroups were too small to allow significant power for a definitive conclusion regarding our findings of no apparent intraocular lens subgroup differences in posterior capsular opacification. Although not one of the main outcome measures of our study, it is an observation of substantial interest and importance to clinicians to notice lower mean intraocular pressure, at significantly reduced medical dependency, in the phacotrabeculectomy group compared with the phacoemulsification group throughout our long-term follow-up (Figure 1). It testifies to the long-term effectiveness of trabeculectomy combined with phacoemulsification with small incision posterior chamber intraocular lens implantation to such an extent that the mean intraocular pressure of the phacotrabeculectomy group can be managed substantially lower than that of the phacoemulsification group. In addition, it is reassuring to confirm that after the modern day advanced cataract surgery, the mean intraocular pressure of the phacoemulsification group is maintained at the mid teens without any noticeable increase of intraocular pressure with time, indicative of apparent rarity, if any, of the late glaucoma development in the great majority of the patients with cataract without preoperative glaucoma or ocular hypertension. In conclusion, the long-term posterior capsular opacification rates did not differ between the patients with cataract who had phacoemulsification and posterior chamber intraocular lens implantation and the patients with glaucoma who had phacotrabeculectomy and posterior chamber intraocular lens implantation. The posterior capsular opacification rates were significantly lower in the patients with diabetes mellitus overall and in the phacotrabeculectomy patients with mitomycin C use.

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