Prospective study of surgical outcomes and bleb morphology using indocyanine green as a surgical dye in trabeculectomy with mitomycin C

Authors


  • Conflict/competing interest: None declared.

  • Funding sources: This work was supported by Capital Vision Research Trust.

Dr Anthony P Wells, Ophthalmology Unit, Wellington School of Medicine, Riddiford Street, Wellington 6021, New Zealand. Email: twells@eyetext.net

Abstract

Background:  To investigate the effect of adding indocyanine green to mitomycin C in augmented trabeculectomy.

Design:  A prospective, non-comparative interventional case series.

Participants:  A total of 37 eyes of 37 patients followed up for 1 year.

Methods:  A solution containing 12.5 mg/mL of indocyanine green was added to mitomycin C, resulting in an mitomycin C concentration of 0.2–0.4 mg/mL, which was applied to bare sclera and Tenon's capsule for 3 min during trabeculectomy.

Main Outcome Measures:  Visual acuity, intraocular pressure, bleb morphology, Moorfields Bleb Grading System scores and complications.

Results:  Indocyanine green could be visualized on clinical examination for all eyes on the first postoperative day. Mean intraocular pressure decreased from 22.9 ± 6.2 mmHg to 12.1 ± 4.4 mmHg postoperatively (P < 0.001) at 1 year. Thirty-four eyes (91.9%) achieved an intraocular pressure of less than 21 mmHg at final visit without additional topical intraocular pressure-lowering medications. Three eyes (8.1%) developed bleb failure andrequired Baerveldt device implantation. There were no cases of blebitis or late bleb leak. No adverse effects attributable to indocyanine green could be identified postoperatively.

Conclusion:  The addition of indocyanine green during trabeculectomy improves the visibility of antimetabolites intraoperatively and allows for the estimation of antimetabolite treatment area intraoperatively and postoperatively. It appears to have no adverse effect on surgical outcomes and complication rates, while improving safety of antimetabolite use.

Introduction

Antimetabolites such as mitomycin C (MMC) and 5-Fluorouracil (5-FU) are commonly used during glaucoma filtration surgery to minimize postoperative subconjunctival scarring and to achieve better intraocular pressure (IOP) control. These antimetabolites are near-colourless and the actual extent of application during surgery is difficult to ascertain. The ability to visualize these agents therefore has distinct advantages: unintentional spillages to the equipment trolley and operative field can be recognized, inadvertent exposure and contact with conjunctival wound edges can be detected, and the extent of treatment area intraoperatively can be easily assessed.1 The addition of a surgical dye to an antimetabolite preparation was pioneered by Healey and Crowston, who demonstrated that trypan blue can be used successfully in this setting without enhancing or reducing the cytotoxic effect of MMC.2

Indocyanine green (ICG) is an anionic dye that has been used intravenously for more than 30 years to investigate the choroidal circulation. When utilized as a surface stain during macular surgery, ICG may persist for more than 2 months.3 We hypothesize that ICG may allow prolonged staining of the Tenon's capsule following trabeculectomy, which will then facilitate postoperative evaluation of antimetabolite treatment area. We have already demonstrated from in vitro experiments with human Tenon's fibroblasts that the addition of ICG to MMC did not significantly alter fibroblast numbers in comparison to MMC alone when measured 7 days after exposure.4 We now report the short- to medium-term surgical outcomes in a cohort of patients undergoing trabeculectomy with routine MMC and ICG adjunct.

Methods

This was a 1-year prospective, non-comparative interventional case series of patients undergoing trabeculectomy with MMC and ICG adjunct. The Tenets of the Declaration of Helsinki were followed and informed consent was obtained from all patients. Patients undergoing trabeculectomy combined with cataract surgery were excluded.

Our approach to fornix-based trabeculectomy has already been described in detail.5 Briefly, following the creation of a fornix-based conjunctival flap and the removal of loose connective tissue from the scleral surface, 10 2 mm by 2 mm sponge fragments presoaked with a mixture of MMC and ICG were applied over a large area of the sub-Tenon's space. The ICG powder (25 mg) was reconstituted with 1 mL sterile water, and then added to 1 mL MMC (concentration between 0.4 and 0.8 mg/mL). This gave a resultant MMC concentration of 0.2 to 0.4 mg/mL and ICG concentration of 12.5 mg/mL. This MMC/ICG mixture was applied for 3 min, during which the assistant ensured that conjunctival wound edge and limbus remained free of antimetabolite by wiping these areas with a dry clean spear. All sponge fragments were subsequently removed and the surgical area irrigated thoroughly with 50 mL balanced salt solution, with particular attention to the conjunctival wound edge if contamination from MMC/ICG mixture was noticeable. Scleral flap was fashioned with adjustable sutures using previously described techniques.6

At the first postoperative day, the adjustable sutures were adjusted transconjunctivally if the IOP was greater than 15 mmHg. Patients were discharged on topical prednisolone 1% six times daily and chloramphenicol 0.5% four times daily. Patients were subsequently reviewed at weeks 1, 3 and 6, and months 3, 6, 9 and 12, in addition to any extra visits deemed clinically necessary. During these postoperative visits, data including best-corrected Snellen visual acuity (converted to its logMAR equivalent for statistical analysis), IOP, bleb morphology and complications were collected. Suture adjustments and/or removal were performed within the 3-week period after surgery if there was persistent IOP elevation greater than 15 mmHg. A combination of subconjunctival injection of 5-FU 50 mg/mL, dexamethasone 4 mg/mL and bleb needling was employed postoperatively if elevated IOP was associated with persistent inflammation and shallow/encapsulated blebs. Bleb morphology was assessed at each visit using commonly used descriptors based on gross bleb appearance (diffuse, cystic, encysted and flat) and the Moorfields Bleb Grading System.5

Surgery was adjudged to be either a complete or qualified success depending on whether additional topical IOP-lowering medications were required to attain IOP of less than 21 mmHg. Failure was prospectively defined as IOP ≥ 21 mmHg or less than 20% reduction below baseline on two consecutive study visits after 3 months, IOP ≤ 5 mmHg on two consecutive follow-up visits after 3 months, requirement for further glaucoma surgery (such as repeat trabeculectomy or glaucoma drainage device insertion, but excluding subconjunctival injections or bleb needling), or loss of light perception due primarily to glaucoma. This classification of failure was based on criteria outlined in the Tube Versus Trabeculectomy Study.7 In addition, the proportion of eyes achieving different IOP upper limits of <18 mmHg, <15 mmHg and <12 mmHg were also calculated for the scheduled follow-up visits. Deterioration in visual acuity was defined as a loss of Snellen visual acuity by greater than one line.

Data analysis was conducted using spss 17.0 statistical software (SPSS Inc., Chicago, IL, USA). Comparison of means was performed with the paired t-test assuming equal variances, but comparison of proportions was performed with the chi-square test. A P-value of 0.05 was considered statistically significant.

Results

A total of 37 patients (one eye from each patient) participated in the study. Table 1 lists the baselinedemographic characteristics of our patient cohort. All these cases had uncontrolled IOP despite maximal tolerated medical therapy. At baseline, the average IOP was 22.9 ± 6.2 mmHg and average logMAR vision was 0.29 ± 0.53. At 1 year, the average IOP had decreased to 12.1 ± 4.4 mmHg (P < 0.001) and the average logMAR vision had worsened to 0.68 ± 1.03 (P = 0.014). The mean IOP on the first postoperative day was 15.8 ± 4.9 mmHg, with 12 (32.4%) eyes requiring transconjunctival suture adjustment to lower IOP. Following suture adjustment, the mean IOP on discharge was 12.8 mmHg (±3.8). ICG was easily visualized in all eyes on the first postoperative day but not during subsequent visits. In total, 24 cases (64.9%) had suture adjustments in the early postoperative period, with 15 cases (40.5%) having further bleb needling (Table 2).

Table 1.  Baseline characteristics of the 37 cases of trabeculectomy with mitomycin C and indocyanine green
CharacteristicNumber
  1. SD, standard deviation; VA, visual acuity; IOP, intraocular pressure.

CasesPatients (eyes)37
Age (years)Mean ± SD67.4 ± 12.8
GenderMale24 (64.9%)
Female13 (35.1%)
LateralityLeft12 (32.4%)
Right25 (67.6%)
DiagnosisOpen angle glaucoma24 (64.9%)
Narrow angle glaucoma6 (16.2%)
Pigmentary glaucoma2 (5.4%)
Steroid induced glaucoma1 (2.7%)
Other secondary glaucoma4 (10.8%)
Preoperative logMAR VAMean ± SD0.29 ± 0.53
Preoperative IOP (mmHg)Mean ± SD22.9 ± 6.2
Preoperative medicationsMean ± SD3.1 ± 0.9
Previous interventionsArgon laser trabeculoplasty2 (5.4%)
Selective laser trabeculoplasty1 (2.7%)
Laser peripheral iridotomy5 (13.5%)
Cataract extraction6 (16.2%)
Trabeculectomy – same eye1 (2.7%)
Trabeculectomy – fellow eye8 (21.6%)
Table 2.  Intraocular pressure (IOP) and bleb outcomes from 37 cases of trabeculectomy with mitomycin C and indocyanine green
CharacteristicNumber
  1. None were on additional IOP-lowering medication, that is, all were complete successes. SD, standard deviation.

IOP at 1 year (mmHg) (excluding cases that required Baerveldt device insertion) 
 Mean ± SD12.1 ± 4.4
 IOP < 21 mmHg34/34 (100.0%)
 IOP < 18 mmHg33/34 (97.1%)
 IOP < 15 mmHg29/34 (85.3%)
 IOP < 12 mmHg17/34 (50.0%)
 IOP ≤ 5 mmHg1/34 (2.9%)
Bleb interventions 
 Mean number of needlings (±SD)1.5 (±1.9)
 None7 (16.2%)
 Suture adjustment only10 (27.0%)
 Needling only6 (18.9%)
 Suture adjustment & needling14 (37.8%)
Additional procedures 
 Repeat trabeculectomy0 (0.0%)
 Baerveldt device insertion2 (5.4%)
 Listed for Baerveldt device1 (2.7%)
 Cyclodiode laser0 (0.0%)
Bleb at 1 year 
 Diffuse22 (59.4%)
 Cystic7 (18.9%)
 Mixed cystic/encysted3 (8.1%)
 Flat2 (5.1%)
 Baerveldt device3 (8.1%)

Table 3 displays the visual acuity results. A significant proportion of eyes (14 cases, 37.8%) demonstrated a decrease in visual acuity at 1 year when compared with baseline. Six eyes (16.2%) suffered loss of Snellen acuity of greater than one line; four eyes (10.8%) had clinically significant cataract, one (2.7%) had a macular hole, and one (2.7%) had failed trabeculectomy with high IOP of 30 mmHg requiring Baerveldt device implantation.

Table 3.  Intraoperative and postoperative complications from 37 cases of trabeculectomy with mitomycin C and indocyanine green
CharacteristicNumber (%)
Mitomycin C concentration 
 Low dose (0.2–0.25 mg/mL)10 (27.0)
 High dose (0.3–0.4 mg/mL)27 (73.0)
Intraoperative complications 
 None33 (89.2)
 Conjunctival tear2 (5.4)
 Abandoned flap site1 (2.7)
 Subconjunctival haemorrhage1 (2.7)
 Iris prolapse0 (0.0)
Suprachoroidal haemorrhage0 (0.0)
Visual acuity at 1 year 
 Worse than at baseline14 (37.8)
 Worse by ≥2 Snellen lines6 (16.2)
  From cataract4 (10.8)
  From macular hole1 (2.7)
  From elevated intraocular pressure1 (2.7)
 No light perception0 (0.0)
Postoperative complications 
 Flat/shallow anterior chamber requiring reformation2 (5.4)
 Wound leak3 (8.1)
 Early hypotony within 1 month1 (2.7)
 Late hypotony1 (2.7)
 Bleb leak0 (0.0)
 Bleb dysaesthesia0 (0.0)
 Blebitis/endophthalmitis0 (0.0)
 Dellen1 (2.7)
 Symptomatic cataract17/31 (54.8)
  Has had cataract surgery6/31 (19.4)
  Awaiting cataract surgery11/31 (35.5)

At 1 year, 22 eyes (59.4%) had a diffuse bleb appearance, seven (18.9%) had blebs with cystic features, and three (8.1%) were mixed cystic/encysted blebs. Figure 1 showed the change in average Moorfields Bleb Grading System score of bleb characteristics over the 12-month study period. When bleb scores at 12 months were compared with day 1, there was a decline in vascularity across all three areas (P < 0.001), an increase in bleb height (P < 0.001) and an increase in maximal bleb area (P = 0.04).

Figure 1.

Average changes in Moorfields Bleb Grading System scores from 37 cases of trabeculectomy with mitomycin C and indocyanine green over a 12-month period. Changes in vascularity parameters were statistically significant (P < 0.001).

Intraoperative and postoperative complications were summarized in Table 3. Three eyes (8.1%) developed early wound leak within the first week of surgery, which settled spontaneously without intervention. Two eyes (5.1%) developed hypotony associated with choroidal effusion at day 30 and day 233, respectively; both settled spontaneously within 2 weeks. Another two eyes (5.4%) developed distorted pupil, shallow anterior chamber and peripheral iridocorneal touch from excessive aqueous drainage at day 11 and day 51, respectively; both required surgical iris repositioning and eventually recovered well with functioning blebs at final visit. There were no cases of late bleb leaks or blebitis were during the follow-up period. None of these eyes had significant intraoperative complications.

Bleb needling was performed in 20 (54.1%) eyes (Table 2), with patients receiving from one to eight needling procedures within the first year. Three eyes (8.1%) developed bleb failure despite repeated bleb needlings and subconjunctival 5-FU and dexamethasone injections; all three eventually required glaucoma drainage device implantation at day 75, 110 and 337, respectively.

The change in mean IOP over the 12-month period is shown in Figure 2. None of our patients with functioning blebs received IOP-lowering medications at any time point after surgery, so these outcomes can be regarded as complete success rates. When failure was defined according to IOP criteria of an upper limit of ≥21 mmHg, reduction of <20% from baseline, or a lower limit of ≤5 mmHg on two consecutive visits after the 3-month follow-up visit, the cumulative failure rate was 24.3% at 1 year (Fig. 3). When the upper IOP limit was lowered to ≥18 mmHg and ≥15 mmHg, the failure rate at 1 year was 27.0% and 32.4%, respectively. None of the eyes developed trabeculectomy bleb failure following cataract extraction.

Figure 2.

Boxplot of intraocular pressure with standard deviation from 37 cases of trabeculectomy with mitomycin C and indocyanine green over a 12-month period (intraocular pressure time points exclude cases that have had Baerveldt device implantation).

Figure 3.

Cumulative probability of failure plots at three different intraocular pressure (IOP) upper limits: ≥21 mmHg, ≥18 mmHg and ≥15 mmHg. IOP criteria for failure were inadequate IOP reduction to below the specific IOP upper limit or IOP reduction ≤20% from baseline or IOP ≤ 5 mmHg on two consecutive visits 3 months after surgery. Repeat glaucoma surgery and loss of light perception vision were also considered failures.

Discussion

The addition of ICG to MMC during trabeculectomy did not appear to cause any adverse outcome to the final IOP or complication rate for this cohort of patients. After a mean follow-up period of 12 months, we achieved IOP ≤ 18 mmHg in 97.1% and ≤15 mmHg in 85.3%, which compares well to results from other case series.8–11 As this is a small-scale, uncontrolled, non-comparative study, we are unable to determine whether improved visualization of MMC directly reduces the incidence of bleb complications, which have already become less common with modern trabeculectomy techniques. It is also possible that a significant reduction in the efficacy of MMC secondary to interactions with ICG may not become apparent until later. Nevertheless, our rates of complication and bleb failure compare favourably with those from the published literature and our own published result.12 None of the complications noted in our cohort of patients could be attributed to the use of ICG intraoperatively.

Modern trabeculectomy is now frequently accompanied by postoperative manipulation of the bleb, of which bleb needling can be considered potentially the most invasive. We performed bleb needling as first line intervention for failing IOP control, instead of topical IOP-lowering medication, in 54.1% of our study subjects. None of the patients experienced any serious or permanent sight-threatening complications, such as endophthalmitis and persistent hypotony. Needling was generally performed weeks after surgery, when there was no longer any trace of ICG in the eye. The rate of bleb needling for this cohort was also similar to our other cases where ICG was not used as a surgical dye.12

As expected, bleb vascularity scores significantly decreased over time as postoperative inflammation settled. An increase in bleb height and maximal bleb area with time corresponded to the establishment of a stable, functioning bleb in the majority of our patients. A minority (23.1%) had cystic bleb changes at final visit, but there were no cases of endophthalmitis, late bleb leaks or blebitis. Longer-term follow up in this group of patients will provide additional information on the safety profile of trabeculectomy with MMC and ICG, since avascular blebs are more likely to develop transconjunctival oozing and bleb leakage with time.13,14

There are several advantages of adding ICG to the MMC preparation. Firstly, it allows intraoperative visualization of the extent of antimetabolite application beyond the sponge contact area. Secondly, the ICG improves sponge visibility and therefore reduces the risk of retained sponges. Thirdly, it allows instant identification of inadvertent antimetabolite spillage and accidental application to the conjunctival wound edge during surgery. Contact between the conjunctival wound edge and MMC is not ideal as it may impair wound healing and result in an increased risk of bleb leak.

As shown in Figure 4, ICG staining is typically visible on the first postoperative day, and the treatment area is well delineated. The persistence of ICG in ocular tissue may allow for more representative measurements of the antimetabolite treatment area postoperatively. This may be an advantage of using ICG over trypan blue, which typically disappears by day 1.2

Figure 4.

Typical day 1 appearance following trabeculectomy with mitomycin C and indocyanine green adjunct. Note the demarcation between antimetabolite treatment area (stained by indocyanine green) and untreated subconjunctival space. The staining was not visible in any patients by day 2.

Our current study is limited by its relatively small sample size and the lack of a control group undergoing augmented trabeculectomy without ICG. In addition, the concentration of ICG used in this study (1.25%) was higher than those from our in vitro experiment (0.0625–0.5%), as we realized from clinical experience that a higher ICG concentration allowed better visualization of the treatment area. In addition, the World Glaucoma Association guidelines recommended that the preoperative baseline IOP be determined from at least three IOP readings (taken at different hours on at least two separate days within a 1-month duration) and that the postoperative IOP be obtained from an at least two IOP measurements during the same visit.15 We were unable to fulfil these recommendations as our study had started before the publication of these guidelines.

In summary, we believe that ICG staining of MMC during augmented trabeculectomy is safe, with no adverse effects on the short- to medium-term surgical outcomes. Like trypan blue, it allows better visualization of MMC and this should improve the safety of antimetabolite use intraoperatively. Its visibility on the first postoperative day allows for quantification of the MMC treatment area, and this may prove useful as a research tool in the future.

Ancillary