Peripheral iridotomy for pigmentary glaucoma

Methodological quality of the review: High confidence

Authors: Michelessi M, Lindsley K

Region: Italy and United Kingdom (UK)

Sector: Glaucoma

Sub-sector: Treament

Equity focus: None specified

Review type: Other review

Quantitative synthesis method: Narrative synthesis

Qualitative synthesis method: Not applicable

Background:

Glaucoma is a chronic optic neuropathy characterized by retinal ganglion cell death resulting in damage to the optic nerve head and the retinal nerve fiber layer. Pigment dispersion syndrome is characterized by a structural disturbance in the iris pigment epithelium (the densely pigmented posterior surface of the iris) that leads to dispersion of the pigment and its deposition on various structures within the eye. Pigmentary glaucoma is a specific form of open-angle glaucoma found in patients with pigment dispersion syndrome.

Topical medical therapy is usually the first-line treatment; however, peripheral laser iridotomy has been proposed as an alternate treatment. Peripheral laser iridotomy involves creating an opening in the iris tissue to allow drainage of fluid from the posterior chamber to the anterior chamber and vice versa. Equalizing the pressure within the eye may help to alleviate the friction that leads to pigment dispersion and prevent visual field deterioration. However, the effectiveness of peripheral laser iridotomy in reducing the development or progression of pigmentary glaucoma is unknown.

Objectives:

Assess the effects of peripheral laser iridotomy compared with other interventions, including medication, trabeculoplasty, and trabeculectomy, or no treatment, for pigment dispersion syndrome and pigmentary glaucoma.

Main findings:

The authors included five randomized control trials (RCTs) (260 eyes of 195 participants) comparing yttrium-aluminum-garnet (YAG) laser iridotomy versus no laser iridotomy. Three trials included participants with pigmentary glaucoma at baseline, and two trials enrolled participants with pigment dispersion syndrome. Only two trials reported the country of enrollment: one – Italy, the other – UK. Overall, the authors assessed trials as having high or unclear risk of bias owing to incomplete or missing data and selective outcome reporting.

Data on visual fields were available for one of three trials that included participants with pigmentary glaucoma at baseline. At an average follow-up of 28 months, the risk of progression of visual field damage was uncertain when comparing laser iridotomy with no iridotomy (risk ratio (RR) 1.00, 95% confidence interval (95% CI) 0.16 to 6.25; 32 eyes; very low-quality evidence). The two trials that enrolled participants with pigment dispersion syndrome at baseline reported the proportion of participants with onset of glaucomatous visual field changes during the study period. At three-year follow-up, one trial reported that the risk ratio for conversion to glaucoma was 2.72 (95% CI 0.76 to 9.68; 42 eyes; very low-quality evidence). At 10-year follow-up, the other trial reported that no eye showed visual field progression.

One trial reported the mean change in intraocular pressure (IOP) in eyes with pigmentary glaucoma: at an average of nine months of follow-up, the mean difference in IOP between groups was 2.69 mmHg less in the laser iridotomy group than in the control group (95% CI −6.05 to 0.67; 14 eyes; very low-quality evidence). This trial also reported the mean change in anterior chamber depth at an average of nine months of follow-up and reported no meaningful differences between groups (mean difference 0.04 mm, 95% CI −0.07 to 0.15; 14 eyes; very low-quality evidence). No other trial reported mean change in anterior chamber depth. Two trials reported greater flattening of iris configuration in the laser iridotomy group than in the control group among eyes with pigmentary glaucoma; however, investigators provided insufficient data for analysis. No trial reported data related to mean visual acuity, aqueous melanin granules, costs, or quality of life outcomes.

Two trials assessed the need for additional treatment for control of IOP. One trial that enrolled participants with pigmentary glaucoma reported that more eyes in the laser iridotomy group required additional treatment between six and 23 months of follow-up than eyes in the control group (RR 1.73, 95% CI 1.08 to 2.75; 46 eyes); however, the other trial enrolled participants with pigment dispersion syndrome and indicated that the difference between groups at three-year follow-up was uncertain (RR 0.91, 95% CI 0.38 to 2.17; 105 eyes). The certainty of evidence for this outcome was graded as very low.

Two trials reported that no serious adverse events were observed in either group among eyes with pigment dispersion syndrome. Mild adverse events included postoperative inflammation; two participants required cataract surgery (at 18 and 34 months after baseline), and two participants required a repeat iridotomy.

The authors concluded based on the findings above that although adverse events associated with peripheral iridotomy may be minimal, the long-term effects on visual function and other patient-important outcomes have not been established.

Methodology: 

Inclusion criteria consisted of randomized control trials (RCTs) that had compared peripheral laser iridotomy versus no treatment or other treatments for pigment dispersion syndrome and pigmentary glaucoma. Primary outcome measures included:

1) proportion of participants with pigmentary glaucoma and progression of visual field loss;

2) proportion of participants with pigment dispersion syndrome with onset of glaucomatous visual field changes as defined in included trials at six months and at one year of follow-up; and

3) mean reduction in IOP from baseline as measured by any method at one year of follow-up.

The authors searched a number of electronic databases including CENTRAL, MEDLINE and EMBASE and clinical trials websites such as (mRCT) and ClinicalTrials.gov. They last searched the electronic databases on 2 November 2015. No date of language restrictions were applied in the searches. The authors also searched reference lists of unidentified trials. Two review authors independently screened articles for eligibility, extracted data, and assessed included trials for risk of bias. To appraise included studies authors used the Cochrane tool specific to intervention-type studies.

The authors did not conduct a meta-analysis of included studies because of in reporting and follow-up intervals for primary and secondary outcomes of interest.

Applicability/external validity:

The authors note that: “A major issue in the applicability of evidence is the variation in participants’ conditions at baseline: Three trials included participants with pigmentary glaucoma and two trials enrolled participants with documented pigment dispersion syndrome with varying IOP criteria and different levels of risk at baseline”.

Geographic focus:

Only two studies reported geographic focus of the trial, Italy and UK.

Summary of quality assessment:

Overall, there is high confidence in the conclusions about the effects of this review. The authors used appropriate methods to screen, extract data and appraise included studies and they appropriately analyzed findings of included studies.