Laser surgery for glaucoma that lowers eye pressure by destroying a part of the eye responsible for production of fluid inside the eye

What is the aim of this review?
The aim of this Cochrane Review was to find out how laser procedures compare to other approaches for lowering the pressure in the eye for people with glaucoma not previously treated with surgery. Cochrane researchers sought and analyzed all relevant studies to answer these questions but found only one study.

Key messages
We do not know whether this type of laser surgery is safer or more effective than other surgeries for treating glaucoma. We included only one study in this review. This study compared low-energy versus high-energy diode lasers, and the results were too similar between treatment groups to draw any conclusions. Additionally, this study did not compare destructive laser surgery to other surgical approaches. More research is needed to understand the usefulness of destructive laser procedures for primary glaucoma treatment.

What was studied in this review?
Glaucoma is a progressive disease of the optic nerve causing loss of vision. It is a common cause of blindness worldwide. When treated early, vision loss may be delayed or prevented.

Intraocular pressure (IOP) is the main treatable risk factor for glaucoma. The ciliary body epithelium produces fluid that builds up pressure in the eye. It is thought that procedures that destroy the ciliary body epithelium, known as cyclodestructive procedures, may reduce IOP as a treatment for glaucoma. Different methods of cyclodestructive procedures are available; the most common is laser. The purpose of this review was to assess laser treatments that destroy the ciliary body epithelium. The review focused on the effectiveness and safety of the included procedures by assessing IOP control, vision, pain control, and side effects.

What are the main results of the review?
We found one study covering 92 people with glaucoma. The study compared low-energy versus high-energy diode transscleral cyclophotocoagulation, a laser procedure to stop production of the fluid in the eye. The trial was conducted in Ghana, and participants were followed for 13 months on average.

Overall, 47% of eyes treated with transscleral cyclophotocoagulation experienced IOP lowering of 20% or more, and there were no differences between the low-energy group and the high-energy group for any of the reported outcomes. IOP control was similar in both treatment groups. The number of medications used after treatment was also similar in both groups. Side effects were not reported separately by treatment group. Information on other important outcomes was not reported.

Based on this review, there is not enough evidence to determine whether transscleral cyclophotocoagulation is an appropriate primary surgical treatment for non-refractory glaucoma, nor whether low-energy or high-energy diode settings are safer or more effective in treating glaucoma.

How up-to-date is this review?
Cochrane researchers searched for studies that had been published up to 7 August 2017.

Authors' conclusions: 

There is insufficient evidence to evaluate the relative effectiveness and safety of cyclodestructive procedures for the primary procedural management of non-refractory glaucoma. Results from the one included trial did not compare cyclophotocoagulation to other procedural interventions and yielded uncertainty about any difference in outcomes when comparing low-energy versus high-energy diode TSCPC. Overall, the effect of laser treatment on IOP control was modest and the number of eyes experiencing vision loss was limited. More research is needed specific to the management of non-refractory glaucoma.

Read the full abstract...
Background: 

Glaucoma is a leading cause of blindness worldwide. It results in a progressive loss of peripheral vision and, in late stages, loss of central vision leading to blindness. Early treatment of glaucoma aims to prevent or delay vision loss. Elevated intraocular pressure (IOP) is the main causal modifiable risk factor for glaucoma. Aqueous outflow obstruction is the main cause of IOP elevation, which can be mitigated either by increasing outflow or reducing aqueous humor production. Cyclodestructive procedures use various methods to target and destroy the ciliary body epithelium, the site of aqueous humor production, thereby lowering IOP. The most common approach is laser cyclophotocoagulation.

Objectives: 

To assess the effectiveness and safety of cyclodestructive procedures for the management of non-refractory glaucoma (i.e. glaucoma in an eye that has not undergone incisional glaucoma surgery). We also aimed to compare the effect of different routes of administration, laser delivery instruments, and parameters of cyclophotocoagulation with respect to IOP control, visual acuity, pain control, and adverse events.

Search strategy: 

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Trials Register) (2017, Issue 8); Ovid MEDLINE; Embase.com; LILACS; the metaRegister of Controlled Trials (mRCT) and ClinicalTrials.gov. The date of the search was 7 August 2017. We also searched the reference lists of reports from included studies.

Selection criteria: 

We included randomized controlled trials of participants who had undergone cyclodestruction as a primary treatment for glaucoma. We included only head-to-head trials that had compared cyclophotocoagulation to other procedural interventions, or compared cyclophotocoagulation using different types of lasers, delivery methods, parameters, or a combination of these factors.

Data collection and analysis: 

Two review authors independently screened search results, assessed risks of bias, extracted data, and graded the certainty of the evidence in accordance with Cochrane standards.

Main results: 

We included one trial (92 eyes of 92 participants) that evaluated the efficacy of diode transscleral cyclophotocoagulation (TSCPC) as primary surgical therapy. We identified no other eligible ongoing or completed trial. The included trial compared low-energy versus high-energy TSCPC in eyes with primary open-angle glaucoma. The trial was conducted in Ghana and had a mean follow-up period of 13.2 months post-treatment. In this trial, low-energy TSCPC was defined as 45.0 J delivered, high-energy as 65.5 J delivered; it is worth noting that other trials have defined high- and low-energy TSCPC differently. We assessed this trial to have had low risk of selection bias and reporting bias, unclear risk of performance bias, and high risk of detection bias and attrition bias. Trial authors excluded 13 participants with missing follow-up data; the analyses therefore included 40 (85%) of 47 participants in the low-energy group and 39 (87%) of 45 participants in the high-energy group.

Control of IOP, defined as a decrease in IOP by 20% from baseline value, was achieved in 47% of eyes, at similar rates in the low-energy group and the high-energy groups; the small study size creates uncertainty about the significance of the difference, if any, between energy settings (risk ratio (RR) 1.03, 95% confidence interval (CI) 0.64 to 1.65; 79 participants; low-certainty evidence). The difference in effect between energy settings based on mean decrease in IOP, if any exists, also was uncertain (mean difference (MD) -0.50 mmHg, 95% CI -5.79 to 4.79; 79 participants; low-certainty evidence).

Decreased vision was defined as the proportion of participants with a decrease of 2 or more lines on the Snellen chart or one or more categories of visual acuity when unable to read the eye chart. Twenty-three percent of eyes had a decrease in vision. The size of any difference between the low-energy group and the high-energy group was uncertain (RR 1.22, 95% CI 0.54 to 2.76; 79 participants; low-certainty evidence). Data were not available for mean visual acuity and proportion of participants with vision change defined as greater than 1 line on the Snellen chart.

The difference in the mean number of glaucoma medications used after cyclophotocoagulation was similar when comparing treatment groups (MD 0.10, 95% CI -0.43 to 0.63; 79 participants; moderate-certainty evidence). Twenty percent of eyes were retreated; the estimated effect of energy settings on the need for retreatment was inconclusive (RR 0.76, 95% CI 0.31 to 1.84; 79 participants; low-certainty evidence). No data for visual field, cost effectiveness, or quality-of-life outcomes were reported by the trial investigators.

Adverse events were reported for the total study population, rather than by treatment group. The trial authors stated that most participants reported mild to moderate pain after the procedure, and many had transient conjunctival burns (percentages not reported). Severe iritis occurred in two eyes and hyphema occurred in three eyes. No instances of hypotony or phthisis bulbi were reported. The only adverse outcome that was reported by the treatment group was atonic pupil (RR 0.89 in the low-energy group, 95% CI 0.47 to 1.68; 92 participants; low-certainty evidence).

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