Combined glaucoma and cataract surgery versus cataract surgery alone for eyes with cataract and glaucoma

Review question
The aim of this systematic review was to compare the effectiveness and safety of combined glaucoma and cataract surgery compared with cataract surgery alone.

Background
Cataract and glaucoma are leading causes of blindness worldwide. Good vision requires a transparent lens in the eye. Cataract is a clouding of the lens that is increasingly common with age. The most common treatment for cataract is surgery, in which the cloudy lens of a person's eye is removed and, usually, replaced with an artificial lens. Glaucoma is a chronic progressive disease of the optic nerve which leads to irreversible vision loss. The most important risk factor associated with glaucoma is high pressure in the eye, known as intraocular pressure (IOP). Thus, glaucoma treatment aims to lower IOP and prevent loss of vision. When medications and laser treatment are no longer able to lower IOP, surgery is necessary. The most common glaucoma surgery is called trabeculectomy, which creates an opening in the wall of the eye to release fluid from within the eye and reduce the IOP.

Since many elderly people have both cataract and glaucoma, the decision to perform both surgeries at the same time or cataract surgery alone must be made. This decision is difficult to make because glaucoma surgery can accelerate cataract progression, cataract surgery can lower IOP independently, and performing both surgeries may increase the rate of complications.

Study characteristics
We included nine studies in which a total of 655 people (657 eyes) were enrolled. Participants had glaucoma and age-related cataract, and each study compared combined cataract and glaucoma surgery versus cataract surgery alone. Seven trials were conducted in Europe, one in Canada and South Africa, and one in the United States. Three trials were conducted at multiple centers, and the follow-up period ranged from 12 to 30 months after surgery. The evidence is current to 3 October 2014.

Key results
We concluded from the available evidence that combined glaucoma and cataract surgery may lead to slightly greater decreases in IOP one year after surgery compared with cataract surgery alone. However, due to differences in the effects among the individual studies and potential for bias in the study results, this conclusion is not definitive. The effect between combined surgery and cataract surgery alone on the rate of complications was uncertain. No information was available for long-term outcomes (five or more years after surgery).

Quality of the evidence
Overall, the quality of the evidence was very low to low due to differences in study characteristics (e.g., type of glaucoma surgery) and poor reporting of outcomes from included studies. These factors may influence the treatment effects when comparing combined glaucoma and cataract surgery versus cataract surgery alone.

Authors' conclusions: 

There is low quality evidence that combined cataract and glaucoma surgery may result in better IOP control at one year compared with cataract surgery alone. The evidence was uncertain in terms of complications from the surgeries. Furthermore, this Cochrane review has highlighted the lack of data regarding important measures of the patient experience, such as visual field tests, quality of life measurements, and economic outcomes after surgery, and long-term outcomes (five years or more). Additional high-quality RCTs measuring clinically meaningful and patient-important outcomes are required to provide evidence to support treatment recommendations.

Read the full abstract...
Background: 

Cataract and glaucoma are leading causes of blindness worldwide, and their co-existence is common in elderly people. Glaucoma surgery can accelerate cataract progression, and performing both surgeries may increase the rate of postoperative complications and compromise the success of either surgery. However, cataract surgery may independently lower intraocular pressure (IOP), which may allow for greater IOP control among patients with co-existing cataract and glaucoma. The decision between undergoing combined glaucoma and cataract surgery versus cataract surgery alone is complex. Therefore, it is important to compare the effectiveness of these two interventions to aid clinicians and patients in choosing the better treatment approach.

Objectives: 

To assess the relative effectiveness and safety of combined surgery versus cataract surgery (phacoemulsification) alone for co-existing cataract and glaucoma. The secondary objectives include cost analyses for different surgical techniques for co-existing cataract and glaucoma.

Search strategy: 

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (2014, Issue 10), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to October 2014), EMBASE (January 1980 to October 2014), PubMed (January 1948 to October 2014), Latin American and Caribbean Health Sciences Literature Database (LILACS) (January 1982 to October 2014), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov), and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 3 October 2014.

We checked the reference lists of the included trials to identify further relevant trials. We used the Science Citation Index to search for references to publications that cited the studies included in the review. We also contacted investigators and experts in the field to identify additional trials.

Selection criteria: 

We included randomized controlled trials (RCTs) of participants who had open-angle, pseudoexfoliative, or pigmentary glaucoma and age-related cataract. The comparison of interest was combined cataract surgery (phacoemulsification) and any type of glaucoma surgery versus cataract surgery (phacoemulsification) alone.

Data collection and analysis: 

Two review authors independently assessed study eligibility, collected data, and judged risk of bias for included studies. We used standard methodological procedures expected by the Cochrane Collaboration.

Main results: 

We included nine RCTs, with a total of 655 participants (657 eyes), and follow-up periods ranging from 12 to 30 months. Seven trials were conducted in Europe, one in Canada and South Africa, and one in the United States. We graded the overall quality of the evidence as low due to observed inconsistency in study results, imprecision in effect estimates, and risks of bias in the included studies.

Glaucoma surgery type varied among the studies: three studies used trabeculectomy, three studies used iStent® implants, one study used trabeculotomy, and two studies used trabecular aspiration. All of these studies found a statistically significant greater decrease in mean IOP postoperatively in the combined surgery group compared with cataract surgery alone; the mean difference (MD) was -1.62 mmHg (95% confidence interval (CI) -2.61 to -0.64; 489 eyes) among six studies with data at one year follow-up. No study reported the proportion of participants with a reduction in the number of medications used after surgery, but two studies found the mean number of medications used postoperatively at one year was about one less in the combined surgery group than the cataract surgery alone group (MD -0.69, 95% CI -1.28 to -0.10; 301 eyes). Five studies showed that participants in the combined surgery group were about 50% less likely compared with the cataract surgery alone group to use one or more IOP-lowering medications one year postoperatively (risk ratio (RR) 0.47, 95% CI 0.28 to 0.80; 453 eyes). None of the studies reported the mean change in visual acuity or visual fields. However, six studies reported no significant differences in visual acuity and two studies reported no significant differences in visual fields between the two intervention groups postoperatively (data not analyzable). The effect of combined surgery versus cataract surgery alone on the need for reoperation to control IOP at one year was uncertain (RR 1.13, 95% CI 0.15 to 8.25; 382 eyes). Also uncertain was whether eyes in the combined surgery group required more interventions for surgical complications than those in the cataract surgery alone group (RR 1.06, 95% CI 0.34 to 3.35; 382 eyes). No study reported any vision-related quality of life data or cost outcome. Complications were reported at 12 months (two studies), 12 to 18 months (one study), and two years (four studies) after surgery. Due to the small number of events reported across studies and treatment groups, the difference between groups was uncertain for all reported adverse events.

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