Different-sized incisions for cataract surgery in people with age-related cataract

Review aim
The aim of this Cochrane Review was to find out if the size of the incision (cut in the eye) during cataract surgery results in a difference in outcome of cataract surgery. We found 26 studies that answered this question.

Key messages
Some, but not all, surgical techniques using smaller incisions were associated with less astigmatism; however, the differences were small and the evidence was uncertain. There was little evidence to suggest any important effects on vision. There were limited data on adverse effects and no evidence on the effects of different-sized incisions on quality of life.

What was studied in this review?
As people age the clear lens in the eye can become cloudy, which is known as a cataract. An operation can be performed to remove the cataract and replace the cloudy lens with a clear artificial lens. This surgery is safe and restores sight in almost all cases. Age-related cataract is one of the leading causes of blindness worldwide.

One problem that can occur after cataract surgery is that due to the surgery the front of the eye is no longer a perfectly curved shape. This can result in blurred or distorted vision and is known as astigmatism. The vision problems arising from astigmatism can be corrected with spectacles. It is commonly believed that the smaller the cut or incision made in the eye during cataract surgery, the less chance of astigmatism.

Key results
We searched for studies that compared different-sized incisions for cataract surgery in people with age-related cataract. This review includes 26 studies from Europe and Asia.

We found the following results.

• Some, but not all, surgical techniques using smaller incisions were associated with less astigmatism, however the differences were small and the evidence was uncertain (low- and very low-certainty evidence).
• In general, there may be little or no difference in visual acuity based on whether a smaller or larger incision is made (low-certainty evidence).
• There were no consistent effects on other signs such as thickness of the cornea (front of the eye) and number of cells in the front of the eye (low- and very low-certainty evidence).
• Adverse effects were not reported by most of the included studies.
• None of the studies reported on the quality of life of participants.

How up-to-date is this review?
We searched for studies published up to 28 October 2016.

Authors' conclusions: 

Phacoemulsification with smaller incisions was not consistently associated with less surgically induced astigmatism compared with phacoemulsification with larger incisions. Coaxial microincision phacoemulsification may be associated with less astigmatism than standard phacoemulsification, but the difference was small, in the order of 0.2 D, and the evidence was uncertain. Safety outcomes and quality of life were not adequately reported; these should be addressed in future studies.

Read the full abstract...
Background: 

Age-related cataract is the principal cause of blindness and visual impairment in the world. Phacoemulsification is the main surgical procedure used to treat cataract. The comparative effectiveness and safety of different-sized incisions for phacoemulsification has not been determined.

Objectives: 

The aim of this systematic review was to assess the effectiveness and safety of smaller versus larger incisions for phacoemulsification in age-related cataract. The primary outcome of this review was surgically induced astigmatism at three months after surgery.

Search strategy: 

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Trials Register) (2016, Issue 10), MEDLINE Ovid (1946 to 28 October 2016), Embase Ovid (1947 to 28 October 2016), PubMed (1948 to 28 October 2016), LILACS (Latin American and Caribbean Health Sciences Literature Database) (1982 to 28 October 2016), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com; last searched 13 May 2013), ClinicalTrials.gov (www.clinicaltrials.gov; searched 28 October 2016), and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp; searched 28 October 2016). We did not use any date or language restrictions in the electronic searches for trials.

Selection criteria: 

We included randomized controlled trials (RCTs) comparing different-sized incisions in people with age-related cataract undergoing phacoemulsification.

Data collection and analysis: 

We used standard methodological procedures expected by Cochrane.

Main results: 

We included 26 RCTs with a total of 2737 participants (3120 eyes). These trials were conducted in Bosnia and Herzegovina, China, France, India, Italy, Korea, Spain, Switzerland, and Turkey. Half of the 26 trials were conducted in China. We judged all trials as mostly at unclear to low risk of bias. The included RCTs compared four different-sized incisions:<= 1.5 mm, 1.8 mm, 2.2 mm, and approximately 3.0 mm. These incisions were performed using three different techniques: coaxial and biaxial microincision phacoemulsification (C-MICS and B-MICS) and standard phacoemulsification. Not all studies provided data in a form that could be included in this review. Five studies had three arms.

Fifteen trials compared C-MICS (2.2 mm) with standard phacoemulsification (about 3.0 mm). Very low-certainty evidence suggested less surgically induced astigmatism in the C-MICS group at three months compared with standard phacoemulsification (mean difference (MD) -0.19 diopters (D), 95% confidence interval (CI) -0.30 to -0.09; 996 eyes; 8 RCTs). There was low-certainty evidence that both groups achieved similar best-corrected visual acuity (MD 0.00 logMAR, 95% CI -0.02 to 0.02; 242 eyes; 3 RCTs). There was low-certainty evidence of little or no difference in endothelial cell loss and central corneal thickness comparing C-MICS with standard phacoemulsification (MD -7.23 cells/mm2, 95% CI -78.66 to 64.20; 596 eyes; 4 RCTs) and (MD -0.68 μm, 95% CI -3.26 to 1.90; 487 eyes; 5 RCTs).

Nine trials compared C-MICS (1.8 mm) with standard phacoemulsification (about 3.0 mm). Very low-certainty evidence suggested less astigmatism at three months in the C-MICS group compared with standard phacoemulsification group (MD -0.23 D, 95% CI -0.34 to -0.13; 561 eyes; 5 RCTs). Low-certainty evidence suggested little or no difference in best-corrected visual acuity, endothelial cell loss, and central corneal thickness in the two groups at three months (MD -0.02 logMAR, 95% CI -0.03 to -0.00; 192 eyes; 3 RCTs), (MD 7.56 cells/mm2, 95% CI -67.65 to 82.77; 380 eyes; 5 RCTs), and (MD -1.52 μm, 95% CI -6.29 to 3.25; 245 eyes; 3 RCTs).

Six studies compared C-MICS (1.8 mm) with C-MICS (2.2 mm). There was low-certainty evidence that astigmatism, visual acuity, and central corneal thickness were similar in the two groups at three months (MD 0.04 D, 95% CI -0.09 to 0.16; 259 eyes; 3 RCTs), (MD 0.01 logMAR, 95% CI -0.01 to 0.04; 200 eyes; 3 RCTs), and (MD 0.45 μm, 95% CI -2.70 to 3.60; 100 eyes; 1 RCT). Very low-certainty evidence suggested higher endothelial cell loss in the 1.8 mm group (MD 213.00 cells/mm2, 95% CI 11.15 to 414.85; 70 eyes; 1 RCT).

Four studies compared B-MICS (<= 1.5 mm) with standard phacoemulsification (about 3.0 mm). Astigmatism was similar in the two groups at three months (MD -0.01 D, 95% CI -0.03 to 0.01; 368 eyes; 2 RCTs; moderate-certainty evidence). There was low-certainty evidence on visual acuity, suggesting little or no difference between the two groups (MD -0.02 logMAR, 95% CI -0.04 to -0.00; 464 eyes; 3 RCTs). Low-certainty evidence on endothelial cell loss and central corneal thickness also suggested little or no difference between the two groups (MD 55.83 cells/mm2, 95% CI -34.93 to 146.59; 280 eyes; 1 RCT) and (MD 0.10 μm, 95% CI -14.04 to 14.24; 90 eyes; 1 RCT).

None of the trials reported on quality of life. One trial reported that no participants experienced endophthalmitis or posterior capsule rupture; they also reported little or no difference between incision groups regarding corneal edema (risk ratio 1.02, 95% CI 0.40 to 2.63; 362 eyes).

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