Does the design of replacement lenses used in cataract surgery help to stop clouding of the new lens once inside the eye?

Key messages
In cataract surgery, replacement lenses that have a sharp edge design may be less likely to develop clouding on their surface than lenses with a round edge. People given new lenses with sharp edges may have clearer eyesight, and may be less likely to need laser surgery, than people given lenses with rounded edges.

How are cataracts treated?
The lens is a small, clear disc inside the eye that focuses light rays to make clear images of objects seen. A cataract starts when cloudy patches develop on the lens. As the cloudy patches get bigger over time, sight becomes misty and blurred.

Surgery is the only way to improve your eyesight if you have cataracts. In cataract surgery, a tiny cut is made in your eye; the old, cloudy lens is removed and a new, plastic lens is put in its place.

After cataract surgery
A common problem after cataract surgery is that the back of the new lens develops cloudy patches on the surface, causing blurred or misty sight again. The problem is treated by using a laser to create a small opening in the back of the lens, to allow light through. However, this procedure could cause further problems, such as raising pressure inside the eye, or could damage other parts of the eye.

Why we did this Cochrane Review
Different styles of plastic lenses have been designed to try to stop or reduce clouding once they are in the eye. Changes include making the edges of the lens round or sharp. We wanted to find out if differently shaped edges on the lens would make it less likely to cloud.

What did we do?
We searched for studies that tested different designs of plastic lenses used in cataract surgery. We wanted to know how differently shaped edges on the lens affected the need for laser eye treatment one year after cataract surgery.

Search date: we included evidence published up to 17 November 2020.

What we found
We found 10 studies involving 1065 people with age-related cataracts who had surgery to replace the lens in 1834 eyes. The studies took place in Austria, Germany, India, Japan, Sweden and the UK. The studies lasted for at least one year. Some studies followed participants for up to 12 years after their surgery.

The studies compared replacement lenses with rounded edges against replacement lenses with sharp edges.

A pharmaceutical company funded one study and partly funded another study.

What are the main results of our review?
In all 10 studies, eyes given a sharp-edged lens showed less clouding on the lens, compared with eyes given a round-edged lens.

- After two, three and five years, eyes given a sharp-edged lens may be less likely to need laser surgery than those given a round-edged lens (evidence from six studies involving 742 people).
- After one year and three years, vision may be clearer in eyes given sharp-edged lenses compared with eyes given round-edged lenses (evidence from two studies involving 260 people).
- At one year after surgery, it was not clear if the design of lens (sharp- or round-edged) affected how many people needed to have laser surgery to treat cloudy patches on the new lens. This might be because not many people in either group needed laser surgery after one year.

We are uncertain how the two designs of lens affected the numbers of any unwanted effects people experienced, because these were not consistently reported. We found no evidence of any important differences between the two lens types in the numbers of complications reported.

None of the studies measured people's well-being.

Our confidence in our results
We are moderately confident about lenses with sharp edges showing a lower average score for clouding than lenses with round edges. Further evidence may increase our confidence in this result. We are less confident about vision being clearer and the lower need for laser surgery for eyes given sharp-edged lenses. Further research is likely to increase our confidence in these results.

Authors' conclusions: 

This review provides evidence that sharp-edged IOLs are likely to be associated with less PCO formation than round-edged IOLs, with less Nd:YAG capsulotomy. The effects on visual acuity were less certain. The impact of these lenses on quality of life has not been assessed and there are only very low-certainty comparative data on adverse events.

Read the full abstract...

Posterior capsule opacification (PCO) is a clouding of the posterior part of the lens capsule, a skin-like transparent structure, which surrounds the crystalline lens in the human eye. PCO is the most common postoperative complication following modern cataract surgery with implantation of a posterior chamber intraocular lens (IOL). The main symptoms of PCO are a decrease in visual acuity, 'cloudy', blurred vision and reduced contrast sensitivity. PCO is treated with a neodymium:YAG (Nd:YAG) laser to create a small opening in the opaque capsule and regain a clear central visual axis. This capsulotomy might cause further ocular complications, such as raised intraocular pressure or swelling of the central retina (macular oedema). This procedure is also a significant financial burden for health care systems worldwide. In recent decades, there have been advances in the selection of IOL materials and optimisation of IOL designs to help prevent PCO formation after cataract surgery. These include changes to the side structures holding the lens in the centre of the lens capsule bag, called IOL haptics, and IOL optic edge designs.


To compare the effects of different IOL optic edge designs on PCO after cataract surgery.

Search strategy: 

We searched CENTRAL, Ovid MEDLINE, Ovid Embase, Latin American and Caribbean Health Sciences Literature Database (LILACS), the ISRCTN registry, and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) up to 17 November 2020.

Selection criteria: 

We included randomised controlled trials (RCTs) that compared different types of IOL optic edge design. Our prespecified primary outcome was the proportion of eyes with Nd:YAG capsulotomy one year after surgery. Secondary outcomes included PCO score, best-corrected distance visual acuity (BCDVA) and quality of life score at one year. Due to availability of important long-term data, we also presented data at longer-term follow-up which is a post hoc change to our protocol.

Data collection and analysis: 

We used standard methods expected by Cochrane and the GRADE approach to assess the certainty of the evidence.

Main results: 

We included 10 studies (1065 people, 1834 eyes) that compared sharp- and round-edged IOLs. Eight of these studies were within-person studies whereby one eye received a sharp-edged IOL and the fellow eye a round-edged IOL. The IOL materials were acrylic (2 studies), silicone (4 studies), polymethyl methacrylate (PMMA, 3 studies) and different materials (1 study). The studies were conducted in Austria, Germany, India, Japan, Sweden and the UK. Five studies were at high risk of bias in at least one domain. We judged two studies to be at low risk of bias in all domains.

There were few cases of Nd:YAG capsulotomy at one year (primary outcome): 1/371 in sharp-edged and 4/371 in round-edged groups. The effect estimate was in favour of sharp-edged IOLs but the confidence intervals were very wide and compatible with higher or lower chance of Nd:YAG capsulotomy in sharp-edged compared with round-edged lenses (Peto odds ratio (OR) 0.30, 95% CI 0.05 to 1.74; I2 = 0%; 6 studies, 742 eyes). This corresponds to seven fewer cases of Nd:YAG capsulotomy per 1000 sharp-edged IOLs inserted compared with round-edged IOLs (95% CI 9 fewer to 7 more). We judged this as low-certainty evidence, downgrading for imprecision and risk of bias.

A similar reduced risk of Nd:YAG capsulotomy in sharp-edge compared with round-edge IOLs was seen at two, three and five years but as the number of Nd:YAG capsulotomy events increased with longer follow-up this effect was more precisely measured at longer follow-up: two years, risk ratio (RR) 0.35 (0.16 to 0.80); 703 eyes (6 studies); 89 fewer cases per 1000; three years, RR 0.21 (0.11 to 0.41); 538 eyes (6 studies); 170 fewer cases per 1000; five years, RR 0.21 (0.10 to 0.45); 306 eyes (4 studies); 331 fewer cases per 1000. Data at 9 years and 12 years were only available from one study.

All studies reported a PCO score. Four studies reported the AQUA (Automated Quantification of After-Cataract) score, four studies reported the EPCO (Evaluation of PCO) score and two studies reported another method of quantifying PCO. It was not possible to pool these data due to the way they were reported, but all studies consistently reported a statistically significant lower average PCO score (of the order of 0.5 to 3 units) with sharp-edged IOLs compared with round-edged IOLs. We judged this to be moderate-certainty evidence downgrading for risk of bias.

The logMAR visual acuity score was lower (better) in eyes that received a sharp-edged IOL but the difference was small and likely to be clinically unimportant at one year (mean difference (MD) -0.06 logMAR, 95% CI -0.12 to 0; 2 studies, 153 eyes; low-certainty evidence). Similar effects were seen at longer follow-up periods but non-statistically significant data were less fully reported: two years MD -0.01 logMAR (-0.05 to 0.02); 2 studies, 311 eyes; three years MD -0.09 logMAR (-0.22 to 0.03); 2 studies, 117 eyes; data at five years only available from one study.

None of the studies reported quality of life. Very low-certainty evidence on adverse events did not suggest any important differences between the groups.

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