Peripheral laser iridotomy for pigmentary glaucoma

Review question
What are the effects of peripheral laser iridotomy compared with other treatments or no treatment for patients with pigment dispersion syndrome or pigmentary glaucoma?

Background
Glaucoma is a chronic eye condition associated with vision loss over time. One of the major risk factors for glaucoma is increased pressure in the eye, known as ocular hypertension. In eyes with pigment dispersion syndrome (PDS), particles from the iris (colored part of the eye) break off from the iris and are deposited on other parts within the eye. Sometimes, these particles block the flow of fluid out of the front portion of the eye, leading to ocular hypertension. Pigmentary glaucoma is a specific form of glaucoma that may be found in patients with PDS. Topcial medical therapy is usually the first-line treatment; however, peripheral laser iridotomy has been proposed as an alternate treatment.

Peripheral iridotomy is a procedure that is performed with a laser. A laser light beam is used to burn a small hole in the iris to create an opening for free movement of fluid within the front portion of the eye. The goal of this procedure is to reduce pressure within the eye, thereby reducing the chance of glaucoma and/or vision loss. However, it is unknown whether peripheral iridotomy reduces the development or progression of pigmentary glaucoma in practice.

Study details
We searched different electronic databases to identify randomized controlled trials evaluating the effectiveness of peripheral iridotomy in people with PDS or pigmentary glaucoma. We included five trials with a total of 260 eyes of 195 participants. Searches were up to date as of 2 November 2015.

Key results
We found no clear benefit for peripheral laser iridotomy versus no laser in eyes with PDS or pigmentary glaucoma in terms of preventing loss of visual field. Very low-quality evidence suggests that laser iridotomy may be more effective in lowering pressure within the eye when compared with no laser iridotomy for up to 10 years after treatment. Few adverse effects were reported among participants in these trials; the most commonly reported adverse events were mild postoperative inflammation and cataract.

Quality of the evidence
We graded the quality of evidence as very low as the result of poor reporting of study methods, incomplete information for meaningful analysis of data, and variation in outcomes assessed among trials. In conclusion, evidence is inadequate to support the use of peripheral iridotomy as treatment for pigmentary glaucoma. Well-designed randomized controlled trials are needed to evaluate the effectiveness and safety of peripheral iridotomy for PDS and pigmentary glaucoma.

Authors' conclusions: 

We found insufficient evidence of high quality on the effectiveness of peripheral iridotomy for pigmentary glaucoma or pigment dispersion syndrome. 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. Future research on this topic should focus on outcomes that are important to patients and the optimal timing of treatment in the disease process (eg, pigment dispersion syndrome with normal IOP, pigment dispersion syndrome with established ocular hypertension, pigmentary glaucoma).

Read the full abstract...
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.

Topcial 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: 

The objective of this review was to 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.

Search strategy: 

We searched a number of electronic databases including CENTRAL, MEDLINE and EMBASE and clinical trials websites such as (mRCT) and ClinicalTrials.gov. We last searched the electronic databases on 2 November 2015.

Selection criteria: 

We included randomized controlled trials (RCTs) that had compared peripheral laser iridotomy versus no treatment or other treatments for pigment dispersion syndrome and pigmentary glaucoma.

Data collection and analysis: 

We used standard methodological procedures for systematic reviews. Two review authors independently screened articles for eligibility, extracted data, and assessed included trials for risk of bias. We did not perform a meta-analysis because of variability in reporting and follow-up intervals for primary and secondary outcomes of interest.

Main results: 

We included five 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 - United Kingdom. Overall, we 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). We graded the certainty of evidence for this outcome 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.

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