What is the best way to place medicines directly into the eye to widen the pupil during cataract surgery?

Key messages
We did not find enough good-quality evidence about the best way to deliver medicines directly to the eye during cataract surgery. We found only one study that had enrolled a large enough number of people to give reliable results.

Larger, well-designed studies are needed to give better estimates of the benefits and potential harms of the different ways of delivering these medicines.

What are cataracts?
A cataract starts when cloudy patches develop on the lens of the eyes. As the cloudy patches get bigger over time, sight becomes misty and blurred. Untreated cataracts will lead to blindness.

Cataract surgery
Surgery is the only way to improve a person's eyesight if they have cataracts. A tiny cut is made in the eye, and the old, cloudy lens is removed and a plastic lens put in its place.

Before and during surgery, doctors use medicines to widen (dilate) the pupil, the dark part in the center of the eye that lets in light. For surgery, the pupil should be as wide as possible to help doctors see and work inside the eye; wide pupils also reduce the chance of problems during surgery.

Why we did this Cochrane Review
Medicines used to widen the pupil can be:

· dropped onto the surface of the eye, as eye drops;

· injected into the eye; or

· released from a tiny device (depot) placed on the surface of the eye beneath the lower eyelid.

We wanted to find out:

· which way of delivering these medicines worked best to widen the pupil during cataract surgery;

· which was the most cost-effective (gave benefits, such as savings in surgery time or costs, that might outweigh any additional costs associated with using it); and

· about any unwanted effects the delivery method might cause.

What did we do?
We searched for studies that tested these different ways of delivering medicines to the eye in people having cataract surgery.

Search date: We included evidence published up to 22 January 2021.

What we found
We found 14 studies in 1652 people (aged 57 to 78 years) who had cataract surgery in 1670 eyes. The studies took place at hospitals in Europe, China, India, and Malaysia. One study reported that it had been sponsored by a company that manufactured one of the depot devices used in the study.

The studies compared eye drops against injections (7 studies) or depot devices (6 studies); one study compared all three delivery types. Unfortunately, there were too many differences between the study designs and results reported to allow us to make overall estimates of how well each method worked.

What are the main results of our review?
The results of the 14 studies comparing eye drops against injections or depot devices did not show sufficiently clear differences between different methods. Not all studies reported results for the measures we were interested in.

We do not know whether one method worked better than either of the others to:

· widen the pupil (measured during surgery, and at the beginning and end of surgery);

· reduce how much time the surgery lasted; or

· reduce how much time it took to replace the lens during surgery.

Not all studies reported on unwanted effects. One study showed that eye discomfort was probably greater with eye drops than with an injection, when measured at one week (555 people) and one month (543 people) after surgery. Another study reported problems with the iris (the colored disc that surrounds the pupil) in 11 people who had an injection, compared with none in the group who had a depot device, although our confidence in these results is limited.

No studies reported on cost-effectiveness of any of the delivery methods.

Our confidence in our results
Our confidence is limited because the results from the studies varied widely, and the studies involved only small numbers of people. Some studies did not clearly report how they were conducted, or whether the people taking part knew who had received which method of delivering the medicine, which could have affected the study's results. Further research is likely to change our results.

Authors' conclusions: 

Data from 14 completed RCTs were inadequate to establish the superiority of any of three methods to achieve mydriasis for cataract surgery, based on pupillary dilation at different times during the surgery or on time required for surgery. Only one trial had a
sample size adequate to yield a robust effect estimate. Larger, well-designed trials are needed to provide robust estimates for the comparison of mydriasis approaches for beneficial and adverse effects.

Read the full abstract...

Cataract surgery is one of the most common surgical procedures performed worldwide. Achieving appropriate intraoperative mydriasis is one of the critical factors associated with the safety and performance of the surgery. Inadequate pupillary dilation or constriction of the pupil during cataract surgery can impair the surgeon’s field of view and make it difficult to maneuver instruments.


To evaluate the relative effectiveness of achieving pupillary dilation during phacoemulsification for cataract extraction using three methods of pupillary dilation: topical mydriatics, intracameral mydriatics, or depot delivery systems. We also planned to document and compare the risk of intraoperative and postoperative complications following phacoemulsification for cataract extraction, as well as the cost-effectiveness of these methods for pupillary dilation.

Search strategy: 

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), which contains the Cochrane Eyes and Vision Trials Register) (2021, Issue 1); Ovid MEDLINE; Embase.com; PubMed; Latin American and Caribbean Health Sciences Literature Database (LILACS); ClinicalTrials.gov; and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). We did not use any date or language restrictions in the electronic search for trials. We last searched the electronic databases on 22 January 2021.

Selection criteria: 

We included only randomized controlled trial (RCTs) in which participants underwent phacoemulsification for cataract extraction.

Data collection and analysis: 

We followed standard Cochrane methodology.

Main results: 

We included a total of 14 RCTs (1670 eyes of 1652 participants) in this review. Of the 14 trials, 7 compared topical versus intracameral mydriatics, 6 compared topical mydriatics versus depot delivery systems, and 1 compared all three methods.

We were unable to calculate overall estimates of comparative effectiveness for most outcomes due to statistical heterogeneity among the estimates from individual studies or because outcome data were available from only a single study. Furthermore, the certainty of evidence for most outcomes was low or very low, due primarily to imprecision and risk of bias.

Comparison 1: topical mydriatics versus intracameral mydriatics

Four RCTs (739 participants, 757 eyes) of the 8 RCTs that had compared these two methods reported mean pupillary diameters at the time surgeons had performed capsulorhexis; all favored topical mydriatics, but heterogeneity was high (I2 = 95%). After omitting 1 RCT that used a paired-eyes design, evidence from three RCTs (721 participants and eyes) suggests that mean pupil diameter at the time of capsulorhexis may be greater with topical mydriatics than with intracameral mydriatics, but the evidence is of low certainty (mean difference 1.06 mm, 95% confidence interval (CI) 0.81 mm to 1.31 mm; I2 = 49%).

Four RCTs (224 participants, 242 eyes) reported mean pupillary diameter at the beginning of cataract surgery; the effect estimates from all trials favored topical mydriatics, with very low-certainty evidence.

Five RCTs (799 participants, 817 eyes) reported mean pupillary diameter at the end of cataract surgery. Data for this outcome from the largest RCT (549 participants and eyes) provided evidence of a small difference in favor of intracameral mydriasis. On the other hand, 2 small RCTs (78 participants, 96 eyes) favored topical mydriatics, and the remaining 2 RCTs (172 participants) found no meaningful difference between the two methods, with very low-certainty evidence.

Five RCTs (799 participants, 817 eyes) reported total intraoperative surgical time. The largest RCT (549 participants and eyes) reported decreased total intraoperative time with intracameral mydriatics, whereas 1 RCT (18 participants, 36 eyes) favored topical mydriatics, and the remaining 3 RCTs (232 participants) found no difference between the two methods, with very low-certainty evidence.

Comparison 2: topical mydriatics versus depot delivery systems

Of the 7 RCTs that compared these two methods, none reported mean pupillary diameter at the time surgeons performed capsulorhexis.

Six RCTs (434 participants) reported mean pupillary diameter at the beginning of cataract surgery. After omitting 1 RCT suspected to be responsible for high heterogeneity (I2 = 80%), meta-analysis of the other 5 RCTs (324 participants and eyes) found no evidence of a meaningful difference between the two methods, with very low-certainty evidence.

Three RCTs (210 participants) reported mean pupillary diameter at the end of cataract surgery, with high heterogeneity among effect estimates for this outcome. Estimates of mean differences and confidence intervals from these three RCTs were consistent with no difference between the two methods. A fourth RCT reported only means for this outcome, with low-certainty evidence.

Two small RCTs (118 participants) reported total intraoperative time. Surgical times were lower when depot delivery was used, but the confidence interval estimated from one trial was consistent with no difference, and only mean times were reported from the other trial, with very low-certainty evidence.

Comparison 3: Intracameral mydriatics versus depot delivery systems

Only one RCT (60 participants) compared intracameral mydriatics versus depot delivery system. Mean pupillary diameter at the time the surgeon performed capsulorhexis, phacoemulsification time, and cost outcomes were not reported. Mean pupil diameter at the beginning and end of cataract surgery favored the depot delivery system, with very low-certainty evidence.

Adverse events

Evidence from one RCT (555 participants and eyes) comparing topical mydriatics versus intracameral mydriatics suggests that ocular discomfort may be greater with topical mydriatics than with intracameral mydriatics at one week (risk ratio (RR) 10.57, 95% CI 1.37 to 81.34) and one month (RR 2.51, 95% CI 1.36 to 4.65) after cataract surgery, with moderate-certainty evidence at both time points. Another RCT (30 participants) reported iris-related complications in 11 participants in the intracameral mydriatics group versus no complications in the depot delivery system group, with very low-certainty evidence. Cardiovascular related adverse events were rarely mentioned.

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