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Year : 2013 | Volume : 1 | Issue : 1 | Page : 4 - 7  


Original Articles
Function of filtering bleb after Cataract Surgery in Eyes with Previous Successful Trabeculectomies

Sneh S. Dhannawat1, R. Ramakrishnan2

1Ophthalmologist, 2Professor of Ophthalmology, Aravind Eye Hospital & PG Institute of Ophthalmology, S.N. High Road, Tirunelveli.

Abstract:

Background: It has been reported that cataract surgery can compromise the function of a filtering bleb, resulting in loss of control of intraocular pressure (IOP). In a number of retrospective studies a rise of IOP after extra capsular extraction and even after phacoemulsification in filtered glaucoma eye was shown. Objective: To evaluate the effect of temporal clear corneal Phacoemulsification with Intraocular Lens implantation (IOL) on IOP control in glaucoma patients who had previous successful trabeculectomy. Methods: The clinical course of 60 patients (60 eyes) who underwent temporal clear corneal phacoemulsification after successful trabeculetomy was studied over a period of 3 years. The number of Primary Open Angle Glaucoma (POAG) and Primary Angle Closure Glaucoma (PACG) cases was equal in our study. Comparison of pre-operative and post-operative IOP, visual acuity, bleb morphology and the number of medications was made at follow up interval of 1 month, 3 months, 6 months and 12 months respectively. Results: The mean ± SD IOP before phacoemulsification was 12.2 ± 4.608 mmHg and it increased to 14.98, 14.47, 15.44 and 15.71 after 1, 3, 6 and 12 months respectively. At each interval the mean IOP was significantly higher than the pre-operative value (p = 0.000, 0.015, 0.000, 0.001 respectively) There was also an increase in the number of antiglaucoma medications used after phacoemulsification. The mean ± SD of medication before phacoemulsification was 0.57 + 0.62 and it increased to 0.65, 0.70, 0.68, 0.67 after 1, 3, 6 and 12 months respectively. But the difference was not statistically significant. Conclusion: Temporal clear corneal phacoemulsification significantly increases IOP in eyes with pre-existing functioning filtering bleb. No statistically significant difference was found between the outcomes of POAG and PACG groups. There is a statistically significant improvement in visual acuity following phacoemulsification with intraocular lens implantation.                                                           

Key Words: Cataract, Filtering surgery, Intraocular pressure, Phacoemulsification, Trabeculectomy

Corresponding Author: Dr Sneh. S. Dhannawat, D.N.B (Ophthalmology)

655 south Fairoaks Avenue, Apt E – 203, Sunnyvale, CA 94086, USA, Email id: drsneh80@gmail.com

 

Introduction:

Glaucoma is a progressive optic neuropathy involving characteristic structural-pathological changes in the optic nerve head [1]. Glaucoma progression is associated with a number of risk factors.

Some of these factors are unmanageable like ethnicity and race, while others can be manipulated, with varying degrees of success, in an attempt to slow or arrest progression, like Intra Ocular Pressure (IOP) and possibly vascular dysregulation. Reducing IOP is presently the evidence based, most accepted, and most practiced therapeutic approach of glaucoma patients [2].

Currently topical ocular hypotensive medications, with its different classes, as well as filtering surgery are in the forefront of therapeutic modalities to reduce IOP.

There is an increased incidence of cataract post trabeculectomy. It is reported to be as high as 20.22 % in a follow up of 12 months [3]. This complication, apart from its deleterious effect on vision, often necessitates another intraocular surgery, which would adversely affect the initial trabeculectomy results. It has been reported that cataract surgery can compromise the function of a filtering bleb, resulting in loss of control of IOP. In a number of retrospective studies a rise of IOP after extra capsular extraction and even after phacoemulsification in filtered glaucoma eye was shown. Our goal was to prospectively investigate the influence of cataract extraction on filtering bleb morphology, function and IOP control in glaucoma eyes with previous successful filtering surgery.

 

Materials and Methods:

A prospective study of 60 eyes of 60 patients, who underwent cataract extraction after successful filtering surgery, was conducted at Aravind Eye Hospital, Tirunelveli, Tamil Nadu. All the cases were studied over a period of 3 years from august 2004-august 2007. All cases underwent temporal clear corneal phacoemulsification. All patients were followed up after 1 month, 3 months, 6 months and 12 months.

Patients with glaucoma who underwent successful trabeculectomy in the past with operable cataract were included. The criteria for exclusion included failed filters, multiple trabeculectomies, juvenile glaucoma, follow up of less than 6 months following cataract surgery and cataract extraction done by Extra Capsular Cataract Extraction (ECCE) or Manual phacoemulsification [Small Incision Cataract Surgery (SICS)].

Informed written consent was obtained from all the patients.

A clear corneal technique for phacoemulsification, and no manipulation of the conjunctiva or filtering bleb was done. Alcon Legacy 20000 series phaco machine was used under Zeiss microscope. All patients were given tapering doses of steroidal drops for fifty days starting from six times a day for first seven days. Cycloplegics were given for first fifteen days whereas antibiotic drops were given for first thirty days.

All cases underwent a standard pre-operative, post-operative evaluation and operative procedures. Records of all patients were maintained especially with respect to visual acuity; best corrected visual acuity, subjective refraction, IOP, optic disc changes and bleb changes. All patients were followed for a minimum period of one year. The intervals between the follow ups were 1 month, 3 month, 6 months and 12 months respectively. Detailed examination included visual acuity, refraction, IOP measurement using Goldman’s applanation tonometer, slit lamp examination with special attention to bleb morphology. We used the Kanski’s classification of filtering bleb to classify the filtering blebs pre-operatively and post-operatively. It is as follows:

Type 1

Bleb has a thin polycystic appearance resulting from transconjunctival flow of aqueous; it is associated with good filtration.

Type 2

Bleb is flat, thin and diffuse with a relative avascular appearance in comparison to the surrounding conjunctiva. This is also indicative of good filtration.

Type 3

Bleb is non- filtering as a result of subconjunctival fibrosis. It is characteristically flat, not associated with micro cystic spaces andcontains engorged blood vessels on its surface.

Type 4

Encapsulated bleb (Tenon’s cyst) is a localized, highly elevated, dome shaped cyst like cavity of hypertrophied tenon’s capsule with engorged blood vessels. The cavity entraps aqueous humor and prevents filtration.

We define good visual acuity in cases were visual acuity on Snellen’s chart was better than or equal to 6/12. Control of IOP following surgery was defined to be complete success if post operative IOP was less than 19 mmHg, Qualified success if IOP was less than 19 mmHg with addition of medications and Failure if IOP was more than 19 mmHg with addition of medications or repeat surgical intervention (bleb needling or repeat surgery). Results were statistically analyzed for IOP reduction, visual improvement, reductions in number of anti glaucoma medications, post-operative complication.

 

Results:

In our study we included 60 eyes of 60 patients which had previous successful filtering surgery with cataract. There were 33 males and 27 females in our study.

Mean age of the patients was 59.93±8.7 and it ranged from 29 to 78.

There were equal number of patients with primary open angle glaucoma and primary angle closure glaucoma in our study. (Table 1)

 Table 1: Types of glaucoma

Type of Glaucoma

No

Primary Open Angle Glaucoma

30

Primary Angle Closure Glaucoma

30

Total

60

 

 

Mean preoperative logmar visual acuity was 0.98±0.4, postoperative logmar visual acuity for Month 1, 3, 6 and 12 were 0.1941 ± 0.20, 0.1881 ± 0.18 and 0.20 ± 0.21 respectively. Significant improvement in visual acuity was found (p < 0.001). Friedman test was used. (table 2)

 

 Table 2: Comparison of pre-operative and post-operative visual acuity (VA)

 

Mean

SD

Minimum

Maximum

Preoperative Logmar VA

0.9805

0.44435

0.30

2.30

Month 1 Logmar VA

0.1941

0.20273

0.00

1.00

Month 3 Logmar VA

0.1881

0.18481

0.00

0.77

Month 6 Logmar VA

0.2002

0.21825

0.00

1.30

 

31.7% of eyes developed fibrosis of the bleb with decrease in the bleb size. 36.7% of eyes in the Primary Angle Closure Glaucoma (PACG) group and 26.7% of eyes in the Primary Open Angle Glaucoma (POAG) group developed fibrosis of the previously elevated bleb. (Table 3 and Graph 1)

 Graph 1 (for table 3): Morphological changes in bleb

 

  Table 3: Morphological changes in bleb

 

Diagnosis

Total

PACG*

POAG#

Bleb remaining the same

Frequency

19

22

41

Percentage

63.3%

73.3%

68.3%

Bleb Fibrosis

Frequency

11

08

19

Percentage

36.7%

26.7%

31.7%

Total

Frequency

30

30

60

Percentage

100%

100%

100%

*Primary Angle Closure Glaucoma

#Primary Open Angle Glaucoma

 

Statistically significant increase in the IOP was found at each post-operative visit. The mean ± SD Intra Ocular Pressure (IOP) before phacoemulsification was 12.42±4.608 mmHg and it increased to 14.98, 14.47, 15.44 and 15.71 after 1, 3, 6 and 12 months respectively. At each interval the mean IOP was significantly higher than the pre-operative value (p=0.000, 0.015, 0.000 and 0.001 respectively). (Table 4 and Graph 2)

 

Table 4: Comparison of pre-operative and post-operative intra-ocular pressure (IOP)

 


 

No

Minimum

Maximum

Mean

SD

P value

Preoperative IOP

60

4 mmHg

24mmHg

12.42

4.608

 

IOP Ist Month

60

10 mmHg

30 mmHg

14.98

4.180

0.0000

IOP 3rd Month

60

10 mmHg

30 mmHg

14.47

3.587

0.015

IOP 6th Month

59

10 mmHg

23 mmHg

15.44

3.602

0.000

IOP 1 year

55

10 mmHg

23 mmHg

15.71

3.473

0.001

 

 

Graph 2 (for Table 4): Comparison of Pre-Operative and Post-Operative Intra Ocular Pressure (IOP)

 

 

There was an increase in the number of anti-glaucoma medications used after phacoemulsification. The mean ± SD number of medications before phacoemulsification was 0.57± 0.62 and it increased to 0.65, 0.70, 0.68, 0.67 after 1, 3, 6 and 12 months respectively. But the difference was not statistically significant. (Table 5a and 5b)

Table 5a:  Comparison of pre-operative and post-operative number of medication

No. of Medications

Pre-Operative

Post-Operative

1st Month

3rd Month

6th Month

12th Month

0

30

26

26

26

26

1

26

29

27

27

23

2

04

05

06

05

04

3

00

00

01

01

02

Total

60

60

60

59

55

 

 Table 5a:  Comparison of pre-operative and post-operative number of medication 

No. of Medications

N

Min

Max

Mean

SD

Pre-Operative

60

0

2

0.57

0.621

1st Month

60

0

2

0.65

0.633

3rd Month

60

0

3

0.70

0.720

6th Month

59

0

3

0.68

0.706

12th Month

55

0

3

0.67

0.771

 

Statistically significant change was not found from pre-operative to month 12 in the Optic Nerve Head (p=0.11). Friedman test was used. (Table 6)

Table 6:  Comparison of pre-operative and post-operative optic nerve head

Optic

Nerve

Head

Pre-

operative

1st

Month

3rd

Month

6th

Month

12th

Month

Mean

0.7436

0.7318

0.7318

0.7318

0.7436

Std. Deviation

0.18335

0.19109

0.19109

0.19109

0.19414

 

The success rates were 83.67%, 86.34%, 73.34% and 71.67% at the end of 1, 3, 6 and 12 months respectively. (Table 7)

 Table 7: Outcome

Follow Up

Failure Rate

Success Rate

1st Month

13.666%

83.67%

3rd Month

16.333%

86.34%

6th Month

26.666%

73.34%

12th Month

28.333%

71.67%

 

Discussion:

Extracapsular cataract extraction after glaucoma filtering surgery has been shown to decrease bleb size and function and result in higher IOP. Phacoemulsification seemed to have fewer side effects on post operative IOP control than did extra capsular extraction [4, 5], however bleb dysfunction may occur [4, 6, 7-9].

In our study, statistically significant increase in the IOP was found at each post operative visit.

Chen et al [10] reported Kaplan Meier success rate of 74%, but only 21% of phacoemulsification procedures were clear corneal incisions. Those investigators found that an age of 50 years or younger, preoperative IOP greater than 10mmHg, iris manipulation, and early postoperative IOP greater than 25mmHg were significantly associated with loss of IOP control. Patients who maintained IOP control without additional medication after surgery had a significantly lower failure rate.

We had equal numbers of PACG and POAG cases (30 each). There was no statistically significant difference in the outcome seen between the two groups (p=0.793) though the number of cases with bleb fibrosis tended to be higher in the PACG group (36.7%). Chen et al [10] have reported uveitic glaucoma associated with higher incidence of IOP loss. Klint et al [11] found no influence of the glaucoma diagnosis on IOP.

Yamagami et al [9] reported that the size of the filtering bleb decreased substantially in 56% of eyes in 2 years after cataract extraction. Chen et al [10] reported a decrease in bleb size in approximately 18% of eyes. Other authors have also observed bleb scarring and shrinkage after cataract extraction, sometimes with worsened IOP control­­. [9, 10, 12]

The response of the body to injury is to initiate a complex process of wound healing, resulting in the formation of fibrous or fibrovascular tissue in which collagen is a major component. This leads to formation of scar, usually a desirable end point. In glaucoma filtering surgery, the goal is to achieve incomplete healing of the surgical wound so as to maintain a functioning bleb.

Successful glaucoma surgery is characterized by passage of aqueous humor from anterior chamber to subconjunctival space, which results in the formation of a filtering bleb. The mechanism that induces IOP elevation and flattening of filtering bleb after cataract surgery is not known. It is likely that the inflammatory response elicited by surgery induces scarring, and although bleb morphology does not always relate to IOP or even trabeculectomy function, [11] this could explain the flattening of the filtering bleb and subsequent IOP increase that occur postoperatively.

Recently, intracameral tissue plasminogen activator has been used successfully to revive six previously functioning but newly failing blebs after phacoemulsification. Large samples are necessary before recommending this approach.

There was significant visual improvement following cataract surgery (p=0.001) in all our patients. Cataract extraction justifies the improvement in the visual fields observed postoperatively.

The limitations of our study include its uncontrolled nature and the relatively small number of patients enrolled. A decrease in IOP over time after successful trabeculectomy, even without nonglaucoma-related surgical interventions, has been reported. [13] Loss of bleb function related to such attrition was not distinguished from that caused by phacoemulsification in this study.

Nonetheless, our finding suggest that in the presence of a functioning filtering bleb, phacoemulsification results in moderate loss of IOP control with a success rate of 58.3% one year after surgery.

Anti-inflammatory treatment after phacoemulsification might also influence the results. The best postoperative anti-inflammatory schedule for these eyes has not been determined, and data regarding this regimen are lacking or imprecise in most studies. [10, 14]

In this study, we reported a statistically significant increase in IOP at each postoperative visit after phacoemulsification, despite the fact that all eyes had a well-functioning filtering bleb before surgery. Moreover, the size of the pre-existing filtering bleb was significantly smaller after phacoemulsification.

These findings indicate that the presence of a functional filtering bleb before surgery does not guarantee long term control after phacoemulsification and intraocular lens implantation.

 

 References:

 

  1. Foster PJ, Buhrmann R, Quigley HA, Johnson GJ. The definition and classification of glaucoma in prevalence surveys. Br J Ophthalmol 2002;86:238-42
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  4. Vesti E. Development of cataract after Trabeculectomy. Acta ophthalmol (Copenh) 1993; 71:777-81
  5. Binkhorst CD, Huber C. Cataract extraction and IOL implantation after fistulizing glaucoma surgery. J Am Intraocular Implant Soc. 1981;7:133 – 7
  6. Mill KB. Trabeculectomy: A retrospective long term follow- up of 444 cases. Br J Ophthalmol 1981; 65:790-5
  7. Obstbaum SA. Glaucoma and IOL implantation. J Cataract Refract Surg., 1986; 12 : 257-61
  8. Murchison JF Jr, Shields MB. An evaluation of three surgical approaches for coexisting cataract and glaucoma. Ophthalmic Surg, 1989; 20:393-8
  9. Yamagami S, Araie M, Mori M, Mishima K. Posterior chamber intraocular lens implantation in filtered or non filtered eyes. Jpn J Ophthalmol 1994; 38:71-9
  10. Chen PP, Weaver YK, Budenz DL, Feuer WJ, Parrish RK 2nd. Trabeculectomy functions after cataract extraction. Ophthalmology 1998;105:1928-35
  11. Klint, Schmitz, Lieb. Filtering bleb function after clear cornea phacoemulsification: A prospective study. Br J Ophthalmology. 2005 May; 89(5):597-601
  12. Dickens M A, Cashwell LF. Long term study of cataract extraction on the function of an established filtering bleb. Ophthalmic Surg Lasers 1996;27:9-14
  13. Kwon YH, Kim CS, Zimmerman MB, Alward WL, Hayreh SS. Rate of visual field loss and long term visual outcome in primary open angle glaucoma, Am J Ophthalmol 2001; 132:47-56
  14. Seah SK, Jap A, Prata JA Jr, Baerveldt G, Lee PP, Heuer DK et al., Cataract surgery after trabeculectomy, Ophthalmic Surg Lasers 1996;27:587-94

 

Source of Support: Nil.

Conflict of Interest: Not Declared.

 

 Pictures:

1. Presence of cataract in an eye with previous successful trabeculectomy

 

 

 2. Clear corneal incision for phacoemulsification

 

3. Immediate post- operative picture


 
 

  1. Three months post -operative

 

 

 

 

 

 

 





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