What did we study in this review?
Glaucoma is a group of eye diseases that cause damage to the nerve in the eye. If left untreated, glaucoma can lead to blindness. Primary angle-closure glaucoma is a type of glaucoma that happens when the drainage canals ('angles') in the eyes get blocked, like a sink with something covering the drain. This blockage may lead to increased eye pressure, resulting in a decrease of the total area in which objects can be seen in side vision ('visual field').
Iridotomy involves using a laser to create a hole in the eye's iris, the colorful disc around the pupil. This opening allows fluid to flow again, which helps control eye pressure and may slow the progression of visual field loss.
What was the aim of this review?
The aim of this Cochrane Review was to find out whether iridotomy compared with no iridotomy can slow progression (or development) of visual field loss in (1) people with primary angle-closure glaucoma, (2) people with primary angle-closure, and (3) people who are suspected of having primary angle-closure.
What were the main results of this review?
We collected and analyzed all relevant clinical trials and identified four eligible trials (3086 eyes of 1543 participants) comparing iridotomy with no iridotomy that addressed our review question.
The four included trials recruited participants from China, Singapore, or the UK who were suspected of having primary angle-closure. One eye of each participant received iridotomy, and the other eye did not receive iridotomy.
Two large studies found that eyes treated with iridotomy likely had wider angles at one year and five years after the treatment, and had less scarring of the drainage channels, which may reduce outflow of aqueous humor (the clear liquid inside the front part of the eye), than eyes that received no iridotomy at five years. The evidence for the effect of iridotomy on drainage channels at one year was uncertain. Our confidence in the evidence for eye pressure and visual acuity is only moderate because of concerns about study design. Unwanted effects related to the treatment, although rare, appeared to be more common in iridotomy-treated eyes than in non-treated eyes.
No studies measured:
• how visual field was affected;
• the number of medications needed to control eye pressure; or
• people's well-being (quality of life).
Key messages
(1) Iridotomy probably changes the internal structure of the eyes (e.g. wider angles) of people with high risk of having primary angle-closure. However, the effects of iridotomy on eye pressure and vision are limited. There is no evidence on visual field change, as no included study reported this outcome.
(2) The included studies only looked at people who were suspected of having primary angle-closure. No evidence is available for other populations.
How up-to-date is the review?
We searched for studies published up to 10 October 2021.
We did not find sufficient evidence to draw any meaningful conclusions on the use of iridotomy for the purpose of slowing progression of visual field loss. No study reported on progressive visual field loss, the primary outcome of this review. Although there is moderate certainty evidence that iridotomy results in improved gonioscopic findings, in is unclear if these findings translate to clinically meaningful benefits.
Primary angle-closure glaucoma is a type of glaucoma associated with a physically obstructed anterior chamber angle. For example, contact between the iris and lens at the pupillary margin creates a pupillary block that increases resistance to aqueous outflow. Obstruction of the anterior chamber angle blocks drainage of fluids (aqueous humor) within the eye and may raise intraocular pressure (IOP). Elevated IOP is associated with glaucomatous optic nerve damage and visual field loss. Laser peripheral iridotomy ('iridotomy') is a procedure to eliminate pupillary block by allowing aqueous humor to pass directly from the posterior to anterior chamber, which is achieved by creating a hole in the iris using laser. Iridotomy is used to treat patients with primary angle-closure glaucoma, patients with primary angle-closure (narrow angles and no signs of glaucomatous optic neuropathy), and patients who are primary angle-closure suspects (patients with reversible obstruction). However, the effectiveness of iridotomy on slowing progression of visual field loss is uncertain.
To assess the effects of iridotomy compared with no iridotomy for primary angle-closure glaucoma, primary angle-closure, and primary angle-closure suspect.
We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2021, Issue 10), which contains the Cochrane Eyes and Vision Trials Register; MEDLINE Ovid; Embase Ovid; PubMed; LILACS; ClinicalTrials.gov; and the WHO ICTRP. The date of the most recent search was 10 October 2021.
Randomized or quasi-randomized controlled trials that compared iridotomy with no iridotomy in primary angle-closure suspects, people with primary angle-closure, or people with primary angle-closure glaucoma in one or both eyes were eligible.
We used standard Cochrane methodology and assessed the certainty of the body of evidence for prespecified outcomes using the GRADE approach.
We identified four studies (3086 eyes of 1543 participants) that compared iridotomy with no iridotomy in participants (range of mean age 59.6 to 62.9 years) who were primary angle-closure suspects from China, Singapore, or the UK. Study investigators randomized one eye of each participant to iridotomy and the other to no iridotomy. Two studies provided long-term (five or more years) results. We judged the certainty of the evidence as moderate to low across the prespecified outcomes, downgrading for high risk of bias (e.g. performance and detection biases) and imprecision of results.
Meta-analyses of data from two studies suggest that iridotomy probably results in little to no difference in IOP compared with no iridotomy at one year (mean difference (MD) 0.04 mm Hg, 95% confidence interval (CI) −0.17 to 0.24; I2 = 65%; 2598 eyes of 1299 participants; moderate certainty evidence) and five years (MD 0.12 mm Hg, 95% CI −0.11 to 0.35; I2 = 0%; 2016 eyes of 1008 participants), and in best-corrected visual acuity measured as logMAR at one year (MD 0.00, 95% CI −0.01 to 0.01; I2 = 69%; 2596 eyes of 1298 participants; moderate certainty evidence) and five years (MD 0.01, 95% CI −0.01 to 0.03; I2 = 0%; 2002 eyes of 1001 participants). In terms of gonioscopic findings, eyes treated with iridotomy likely had wider angles in Shaffer grading scale (MD 4.93 units, 95% CI 4.73 to 5.12; I2 = 59%; 2598 eyes of 1299 participants at one year; MD 5.07, 95% CI 4.78 to 5.36; I2 = 97%; 2016 eyes of 1008 participants at five years; moderate certainty evidence) and experienced fewer peripheral anterior synechiae (PAS) than eyes that received no iridotomy at five years (risk ratio (RR) 0.41, 95% CI 0.24 to 0.67; I2 = 28%; 2 studies, 2738 eyes of 1369 participants), but the evidence was less conclusive at one year (RR 0.62, 95% CI 0.25 to 1.54; I2 = 57%; 3 studies, 2896 eyes of 1448 participants; low certainty evidence). No studies reported data on the proportion of participants with progressive visual field loss during follow-up (the primary outcome of this review), mean number of medications to control IOP, or quality of life outcomes. Low certainty evidence suggests that iridotomy may result in little to no difference in the incidence of acute angle-closure (RR 0.29, 95% CI 0.07 to 1.20; I2 = 0%; 3 studies, 3006 eyes of 1503 participants). Other ocular adverse events (e.g. eye pain, dry eye, redness of eyes, and ocular discomfort), although rare, were more common in eyes treated with iridotomy than in eyes in the control group.