Effect of Phacoemulsification on Intraocular Pressure Control in Primary Open Angle Glaucoma Previously Treated by Trabeculectomy: A Case-Control Study

doi:10.4236/ojoph.2012.22004

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Open Journal of Ophthalmology, 2012, 2, 14-20

http://dx.doi.org/10.4236/ojoph.2012.22004 Published Online May 2012 (http://www.SciRP.org/journal/ojoph)

Effect of Phacoemulsification on Intraocular Pressure

Control in Primary Open Angle Glaucoma Previously

Treated by Trabeculectomy: A Case-Control Study

Samir Aziz1*, Nicky Spiers2, Jeffrey Jay3

1Moorfields Eye Hospital NHS Foundation Trust, London, England; 2Tennent Institute of Ophthalmology, Gartneval General Hospi-

tal, Glasgow, Scotland; 3University of Leicester, Leicester, England.

Email: *[email protected]

Received December 26th, 2011; revised January 19th, 2012; accepted February 9th, 2012

ABSTRACT

Purpose: To analyse the effect of phacoemulsification on the control of intraocular pressure in primary open angle

glaucoma in patients having phacoemulsification after previous trabeculectomy and compare them with a control group

who had trabeculectomy alone. Patients and Methods: Twenty one patients (one eye from each) who had phacoemul-

sification subsequent to trabeculectomy were identified, and compared with 41 controls. Intraocular pressure, bleb ap-

pearance, glaucoma medications, iris manipulation and complications were recorded. Each patient was followed for full

12 months. Failure of control was defined as follows: 1) intraocular pressure >21 mm Hg on medication, or 2) a greater

number of glaucoma medications than before phacoemulsification. Results: The post operative change in intraocular

pressure in the case group at 12 months was much less than that in the control (p = 0.001). The mean intraocular pres-

sure had changed from 15.3 mm Hg to 14.7 mm Hg. The control group showed an average intraocular pressure reduc-

tion of 6 mm Hg at the last visit (p > 0.001). In phacoemulsification group, 19% required 1 or 2 glaucoma medications

at one year follow-up vs 19.5% in the control group. In phacoemulsification group, 9.5% showed flattening of a previ-

ously formed bleb at the last visit (P < 0.001), compared with 9.7% of controls. Conclusions: The stability of glaucoma

control in the first year after phacoemulsification in previously filtered eyes with primary open angle glaucoma is com-

parable to that of the natural course after trabeculectomy. The study is limited by the small number of cases available.

Keywords: Phacoemulsification; Trabeculectomy; Cataract; Glaucoma

1. Introduction

Glaucoma and cataract often coexist in the same eye [1,2]

not only because they both occur in the elderly popula-

tion, [3,4] but also because antiglaucoma medications

may contribute to the formation and development of

cataract [1]. In addition, glaucoma filtering surgery may

accelerate cataract formation [5,6], possibly in 14% -

40% of patients [7,8].

One of the accepted surgical options in patients with

severe glaucoma and coexisting cataract is first to control

the intraocular pressure (IOP) with trabeculectomy and

then extract the cataract several months later [9]. There-

fore, the management of visually significant cataract in a

glaucoma patient who has had a previous trabeculectomy

is a common clinical problem [1,10,11].

Several studies have examined the effect of phacoe-

mulsification (PE) [1,10,11,12-14] and extracapsular

cataract extraction (ECCE) [1,10,11,12-13] on interme-

diate and long-term IOP control after trabeculectomy,

with conflicting results. When cataract surgery is per-

formed in filtered eyes there is a risk of early postopera-

tive increase in IOP and loss of long-term IOP control [3,

6,14-18]. Others have found that IOP control can be re-

tained after cataract extraction by increasing antiglau-

coma medications [10], while some report that increased

IOP is not observed in patients with previous filtering

surgery and that none of their patients required additional

antiglaucoma medications [19].

More specifically, the effect of ECCE technique on fil-

tering blebs has been investigated [10,12,13]. Ten to

thirty-eight percent of eyes with previous trabeculectomy

require additional medication or further glaucoma sur-

gery to maintain IOP after ECCE with IOL implantation

[10,13,14]. Phacoemulsification seems to have fewer

adverse effects on the postoperative IOP control than

ECCE; however, bleb dysfunction may still occur in the

postoperative period [10,13,15,18,20].

In this retrospective study we quantitatively analyze

*Corresponding author.

Effect of Phacoemulsification on Intraocular Pressure Control in Primary Open Angle Glaucoma Previously

Treated by Trabeculectomy: A Case-Control Study

the effect of PE on the control of IOP in POAG in pa-

tients having PE after previous trabeculectomy (trabe-

culectomy-phacoemulsification group). In order to allow

for any intrinsic instability of IOP control after trabe-

culectomy undisturbed by PE, we compare them with a

control group who underwent trabeculectomy alone (tra-

beculectomy group).

2. Patients and Methods

A retrospective and consecutive case note review was

performed on 21 Caucasian patients who had trabeculec-

tomy for uncontrolled POAG followed by PE at Gartna-

vel General Hospital in Glasgow, UK. A trabeculectomy-

phacoemulsification (TP) group was compared with the

control group (41 consecutive Caucasian patients) who

had trabeculectomy (T) alone for uncontrolled POAG

without cataract surgery at the same hospital. Patients

with other types of glaucoma or who had received anti-

metabolites during or after the trabeculectomy were ex-

cluded. Each patient was followed for full 12 months

after PE and trabeculectomy respectively. Only one eye

of each patient was included.

The following data were obtained for each patient in

both groups: gender, age, bleb appearance, number and

type of glaucoma medications, previous ocular surgeries,

time elapsed between T and PE, IOP preceding surgery,

and IOP at 1 day, 1 week, 3, 6, 9, and 12 months after

surgery, intraoperative iris manipulation (posterior sy-

nechialysis, stretching, sphincterotomies and iridectomy),

intraoperative and postoperative complications, postop-

erative medications administered, and the dates when

additional glaucoma medications were added. At the fi-

nal visit, the number of glaucoma medications, IOP and

bleb appearance were documented.

In the TP group, phacoemulsification was performed

in 21 patients by several experienced surgeons, using a

3.2 mm superior clear-corneal incision. A foldable poste-

rior chamber acrylic, hydrophobic lens (IOL) was in-

serted in the capsular bag. Small pupils were surgically

enlarged by iris manipulation. In no case was an anterior

chamber IOL inserted.

In all patients of both groups, same technique of T was

performed by one surgeon (J.J.); using a fornix based

conjunctival flap, however less than 5 were done by ex-

perienced surgeons who followed the same technique

under his direct supervision. Post operative medications

included topical corticosteroid and antibiotic drops used

4 times daily for 4 weeks in both groups. Cycloplegic

drops were administered twice daily for 2 weeks after T.

Intraocular pressure, bleb appearance, and number of

glaucoma medications were compared between the 2

groups.

For the purposes of the study and for comparison with

other studies, we used two criteria to define failure: 1) an

IOP greater than 21 mm Hg on medication, or 2) a

greater number of glaucoma medications than before PE.

Patients who had received antifibrotics were excluded.

Outcomes were compared between the two groups us-

ing the Mann-Whitney U test, Chi square and Student’s

t-test where appropriate. Random effects models with

normal errors were fitted to the IOP profiles for months 1,

3, 6, 9 and 12 using Proc Mixed in SAS. Because of great

variability in pressures in the first month, measures taken

prior to one month post-operatively were not modeled.

Models were compared using the Likelihood Ratio Test.

Differences were considered significant at the 5% level.

3. Results

The patient’s characteristics are shown in Table 1. There

is a difference between the mean ages in the 2 groups.

The mean time between T and PE was 52.6 months (SD

22.6, range 16 - 93). In the TP group, 9.5% (n = 2, Table

2) showed flattening of a previously formed bleb at one

year follow-up (P < 0.03). The trabeculectomy group was

similar (9.7%, n = 4).

The mean IOP of the case group one year after PE had

fallen very slightly from 15.3 mm Hg (SD 4.5, range 10 -

25) preoperatively to 14.7 mm Hg (SD 3.5, range 10 -

22). However, one patient had an IOP of 22 mm Hg at

the latest examination. At the last visit, patients who re-

quired antiglaucoma medications after PE had a mean

IOP before PE of 21.5 mm Hg (SD 1.7, range 20 - 23),

which was higher than those controlled without glau-

coma medication 14 mm Hg (SD 3.9, range 10 - 25).

The post operative change in IOP in the TP group at

12 months was much less than the change in IOP fol-

lowing trabeculectomy (Median change 0 versus –6 p =

0.001; Mann-Whitney U test).

The control group showed an average IOP reduction of

6 mm Hg in the last visit (p > 0.001). There was no evi-

dence that the difference in mean IOP between the

groups varied with time, or that there was any change in

between subjects variation in pressure. The best fitting

model had parallel quadratic mean profiles for the case

and control groups, with an increase in mean IOP over

time (Figures 1 and 2). Figure 1 also confirms that the

curves for long term change in IOP are similar in both

groups.

The estimated mean IOP profile shown in Figure 1 is

higher for cases than for controls, but this difference was

not significant (mean difference 0.85 mm Hg; 95% CI

–0.84 to 2.54).

Two outliers in the control group were not well fitted

Effect of Phacoemulsification on Intraocular Pressure Control in Primary Open Angle Glaucoma Previously

Treated by Trabeculectomy: A Case-Control Study

Table 1. Characteristics of patients in the two groups.

Trabeculectomy

Trabeculectomy-

Phacoemulsification P-value Test

Diagnosis POAG 41 21

Age (years) Mean (range) 74 (57 - 87) 78 (61 - 91) 0.01 Unpaired t-test

Sex 0.24 Chi square

Male 20 7

Female 21 14

IOP (mean) Baseline 15.3 (10 - 25) 14.7 (10 - 22)

Postoperative 21 (15 - 31)* 15 (7 - 26)†

Elapsed time between glaucoma and

cataract surgeries (months) Mean (range) N/A 52.6 (16 - 93)

Iris manipulation 5

POAG: primary open angle glaucoma; IOP: intraocular pressure; *: 12 months post trabeculectomy; †: 12 months post phacoemulsification.

by the model. ID 121 had unusually high IOP throughout.

ID 140 had an unusual increase in IOP from 6 at month 1

to 22 at month 3 and persisted at that level. When the

final model was refitted with these two subjects included

there was a slight increase in the difference in means

between groups (Table 3), but the difference in mean

profiles between the groups did not reach significance in

either model.

129631

months postoperative

18.00

17.00

16.00

15.00

14.00

13.00

12.00

IOP (mmHg)

case

control

group

There was one missing value at month 9 in the case

group. The other values for this individual were included

in the analysis, and the missing value is not considered to

have any bearing on the conclusions.

In the PE group, 4 patients (19%) required 1 or 2

glaucoma medications at one year (Table 2). One had

high IOP preoperatively; the other had required treatment

prior to PE. In the trabeculectomy group eight patients

(19.5%) used glaucoma medication one year after T, and

5 of them used a single medication. Iris manipulation

was required in 5 patients (3 posterior synechialysis, 1

stretching, and 1 sphincterotomy) to disrupt posterior

synechiae during cataract surgery in the PE group; three

of these needed glaucoma medications in the first month.

However, IOP was controlled thereafter without lowering

drops.

Figure 1. Predicted mean intraocular pressure from final

model, with 95% confidence intervals.

In the TP group there were postoperative IOP spikes in

8 eyes (38%) on the first day and in a further 2 eyes in

the first week. In the same group, endophthalmitis de-

veloped in one eye one week postoperatively, it was

successfully treated with intravitreal amikacin, it retained

a VA (visual acuity) of 6/60 in the last visit.

4. Discussions

Figure 2. Real values of intraocular pressure in both

groups. Cataract extraction in eyes functioning filtering with a

Effect of Phacoemulsification on Intraocular Pressure Control in Primary Open Angle Glaucoma Previously

Treated by Trabeculectomy: A Case-Control Study

Table 2. Intraocular pressure, number of medications and bleb appearance in the case group.

IOP (mm Hg) Number of me d ications

Case Preop Last visit Preop Last visit Bleb appearance

1 14 16 0 0 NC

2 14 12 0 0 NC

3 19 12 0 0 NC

4 10 12 0 0 NC

5 14 13 0 0 NC

6 13 18 0 0 NC

7 12 19 0 0 NC

8 11 18 0 0 NC

9 20 14 1 1 NC

10 14 12 0 0 NC

11 13 14 0 0 NC

12 20 10 1 1 Flattened

13 23 22 0 1 Flattened

14 14 12 0 0 NC

15 10 19 0 0 NC

16 15 17 0 0 NC

17 10 10 0 0 NC

18 25 12 0 0 NC

19 23 12 0 2 NC

20 14 15 0 0 NC

21 14 20 0 0 NC

IOP: intraocular pressure; NC: no change.

Table 3. Mean difference in intra ocular pressure (IOP) profiles from random effects model.

Model N Difference in mean IOP (Case-control) LCL UCL P-value for difference

1 62 0.77 –0.99 2.53 0.39

2 (Outliers excluded) 60 1.05 −0.54 2.64 0.20

N: number; IOP: intraocular pressure; LCL: lower 95% confidence limit; UCL: upper 95% confidence limit.

bleb is considered to be a risk [17]. Small incision cata-

ract surgery is the technique of choice in this group [1,

16], because there is less conjunctival dissection and in-

flammation [1]. Several studies report that PE has a

minimal effect on the long-term mean IOP after T [2,10,

12]. However, PE may jeopardize a previously function-

ing filtering bleb and result in increase in IOP [4,11,

15,18].

This study is an attempt to isolate the IOP as one spe-

cific aspect of glaucoma and to determine if that single

factor is affected by later PE.

We did not include visual field since it might be in-

fluenced by lens opacities [21]. We showed that the IOP

in the TP group at up to one year after PE was not sig-

nificantly altered. Other studies (Table 4) have shown

variable results and in some, either no significant differ-

ence or a decrease in IOP was detected [10,11,14,22,23].

Park et al. [14] used a control group that had T alone and

showed that PE seemed to have no effect on IOP control

after PE. However, unlike our study their case-control

study was not limited to cases of POAG. Furthermore,

antimetabolites had been used which might have affected

Effect of Phacoemulsification on Intraocular Pressure Control in Primary Open Angle Glaucoma Previously

Treated by Trabeculectomy: A Case-Control Study

Table 4. Summary of studies on the effects of phacoemulsification in eyes with filtering blebs.

Study No. Follow-up (m)Success (%)Definition of success

Seah et al. [13] 6 13.6 67 IOP < 19 mm Hg with no additional surgery and no additional

medications

Chen et al. [10] 57 17.6 74 No additional medications, bleb needling, or glaucoma surgery

Park et al. [14] 40 20.1 80 (3 yrs) No greater number of medications: IOP ≤ 21 mm Hg or >20% re-

duction on 2 consecutive visits compared with pretrabeculectomy

Manoj et al. [11] 21 15.1 100 IOP < 18 mm Hg and within the target pressure

Crichton & Kirker [15] 69 23.2 77 No additional surgery and no additional medications compared

with pre cataract

Rebolleda & Munoz-Negrete. [17] 49 19.5 67.4 No glaucoma medications, surgery, or bleb needling to control IOP

Ehrnrooth et al. [4] 46 25.3 69.5 IOP ≤ 21 mm Hg with no additional surgery and no or single

topical medications

Present study 21 12 85.7 IOP ≤ 21 mm Hg with no additional surgery and no additional

medications

the outcome, in contrast to our study where patients who

had received antimetabolites were excluded in order to

reduce case mix and subsequently bias.

On the other hand, the most frequent conclusion is that

there is an increase in IOP after PE [1,10,12,15,17,19,

23-25].

Our aim was to describe the changes provoked by a

second surgical procedure. When the time between tra-

beculectomy and PE was greater than 1 year the interval

between surgeries had no effect on bleb failures, IOP, or

medication changes [17]. In our study cohort, the time

between T and PE is rather long, since we feel that most

of them do not need cataract surgery earlier than that.

The success rate after 1 year in our TP group was

85.7%, Table 4 shows the success rate reported in the

literature. The rate varies between 67% and 100% but the

definition of success is slightly different in the different

studies and not all included a control group. Most of the

failures occurred between 6 and 24 months after PE, in-

dicating that the effect on bleb filtration is a delayed re-

sponse [26].

There is a recognized trend for a late rise in IOP after

T [18]; therefore PE might not be the only possible ad-

verse influence on IOP [27]. A decrease in IOP over time

after successful T has been reported [28]. In our study,

allowing for the possible change in long term IOP control

after T, PE seemed to have no additional effect on IOP

control.

The use of glaucoma medications is similar in the case

(19%) and control (19.5%) groups. This figure matches

one other study (20%) [15]. But most authors report

more frequent use of medications [10,14]; (22%) [29],

(34.7%) [17], (49.4%) [2], (41%) [4]. In our study, the

number of glaucoma medications did not change much in

the TP group during the course of the study, whereas in

the T group 9% required additional pressure-lowering

medications.

Evaluation of bleb morphology in retrospective studies

without standardized criteria is difficult and very subjec-

tive. We found flattening of the bleb in 9.5% and 9.7% in

the case and control groups respectively. Others have

found this to be more frequent (77.6%) [17], (18%) [10].

It is likely that the inflammatory response elicited by

surgery induces subconjunctival scarring [20]. This could

explain the flattening of the filtering bleb and subsequent

IOP increase that may occur even after the relatively

atraumatic PE procedure [10,12,13,17,29]. The presence

of a functional filtering bleb before surgery does not

guarantee long-term IOP control after PE [17].

In our study, PE was performed at least 16 months af-

ter T, and under these conditions, the time between T and

PE did not seem to influence failure, glaucoma medica-

tion use or IOP changes. Some authors believe that the

filtering bleb needs sufficient time (>5 months) [14], (≥6

months) [24], or (≥1 year) [13] to develop properly since

the inflammation associated with cataract surgery may

induce bleb failure [10]. However, others showed no

association between IOP control and the timing of cata-

ract surgery [14].

Iris manipulation in our study seemed not to be associ-

ated with poor IOP control, bleb failure or need for addi-

tional medications. Similar findings were reported by

others good IOP control [18,27], no bleb failure [10,13]

no additional medications [15,16,24]. Other studies did,

however, find an association with bleb failure [24,27].

Severe postoperative complications after PE were rare

in our study. Early postoperative IOP spikes are fre-

quently observed after cataract surgery in glaucomatous

eyes. We observed an IOP spike of ≥8 mm Hg in 4 eyes

(19%) 1 day after PE. A prospective study by Rebolleda

Effect of Phacoemulsification on Intraocular Pressure Control in Primary Open Angle Glaucoma Previously

Treated by Trabeculectomy: A Case-Control Study

& Muñoz-Negrete [17] found a similar rate (18.4%, IOP

> 10 mm Hg). Others have reported higher (57%) [30],

(50%) [14], (37%) [14], or lower rates (6.3% ≥ 30 mm

Hg) [24].

Intraocular pressure fluctuations during the first post-

operative months after routine cataract extraction are

well known [11].

Our study used only eyes with POAG, which carries

the best prognosis for T. Therefore, our favorable obser-

vations may not be extrapolated to other types of glau-

coma where a successful drainage fistula might more

readily be compromised by subsequent PE.

There is 4 year age difference between both groups;

however we do not feel that this is a source of clinically

meaningful bias. Our study has the benefit of a control

group which enables us to make allowance for the

change in IOP which might occur after T. Another

strength is the analysis of repeated measurements of IOP

during the year which allowed a detailed comparison of

the behavior of the IOP in the two groups.

Limitations of this study are its retrospective nature

and the lack of statistical significance; this may be attrib-

utable to the relatively small sample size.

We conclude that the stability of glaucoma control in

the first year after PE in previously filtered eyes with

POAG is comparable to that of the natural course of T.

A future, large, prospective and controlled study could

provide more reliable data about the effect of PE on the

function of a previous fistulising operation.

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