Toric intraocular lenses versus limbal relaxing incisions for astigmatism in cataract surgery

What is the aim of this review?
The aim of this Cochrane Review was to find out how toric intraocular lenses (IOLs) compare with limbal relaxing incisions (LRIs) for correcting astigmatism during cataract surgery. Cochrane researchers collected and analysed all relevant studies to answer this question and found 10 studies.

Key messages
The review shows that toric IOLs probably provide a higher chance of a good outcome with respect to astigmatism after cataract surgery compared with LRIs. The difference in average astigmatism may be small and there may be little or no difference in vision or quality of life. There was a lack of evidence on which of these techniques represents best value for money. 

What was studied in the review?
As people get older, the lens within the eye can become cloudy: this is known as a cataract. Eye doctors can perform an operation to remove the cataract and replace it with a clear artificial IOL. The clear window at the front of the eye (the cornea) focuses light onto the ‘film’ at the back of the eye (the retina). The normal cornea is not perfectly dome-shaped; it is commonly described as being shaped like a rugby ball. Because of this shape, the eye focuses light imperfectly onto the retina and this is known as astigmatism. It is measured in units called dioptres. In most eyes, astigmatism is slight and does not cause any symptoms. In some people, astigmatism is large enough to cause significant visual blurring. Usually this astigmatism is corrected by spectacles. However, during cataract surgery there are two possible ways of correcting the astigmatism, either by putting in a special "toric" lens, or by performing special incisions known as limbal relaxing incisions. Cataract surgery is a common operation and astigmatism is also a common condition. In order to achieve best possible vision after surgery for people with astigmatism it is important to understand the best way to correct it.  

What are the main results of the review?
Cochrane researchers found 10 relevant studies. These studies took place in China (three studies), UK (three), Brazil (one), India (one), Italy (one) and Spain (one). The studies compared toric IOLs with LRIs for people with astigmatism who were having cataract surgery.

Cochrane researchers assessed how certain the evidence is for each review finding. They looked for factors that can make the evidence less certain, such as problems with the way the studies were done, very small studies, and inconsistent findings across studies. They graded each finding as very low-, low-, moderate- or high-certainty.

The review shows that:

⇒  People receiving toric IOLs were probably more likely to achieve a good outcome with respect to astigmatism (that means astigmatism of less than 0.5 dioptres) six months or more after surgery compared to people receiving LRIs  (moderate-certainty evidence).  ⇒ On average, there may be a small difference in astigmatism between the two groups after surgery, favouring toric IOLs (low-certainty evidence).

⇒ People receiving a toric IOL probably have a small improvement in visual acuity at six months or more after surgery compared to people receiving LRIs, but the difference is small and may be clinically unimportant (moderate-certainty evidence).

⇒ There may be little difference in vision-related quality of life (low-certainty evidence). 

⇒ People receiving toric IOLs may be more likely not to require spectacles to achieve their best distance vision compared with people receiving LRIs (low-certainty evidence).

⇒ There was only very low-certainty evidence on adverse effects.

⇒ Cochrane researchers found no economic studies that compared toric IOLs with LRIs.

How up-to-date is this review?
Cochrane researchers searched for studies that had been published up to September 2019.
 

Authors' conclusions: 

Toric IOLs probably provide a higher chance of achieving astigmatism within 0.5 D after cataract surgery compared with LRIs. There may be a small mean difference in postoperative astigmatism, favouring toric IOLs, but this difference is likely to be clinically unimportant. There was no evidence of an important difference in postoperative visual acuity or quality of life between the techniques. Evidence on adverse effects was uncertain. The apparent shortage of relevant economic evaluations indicates that economic evidence regarding the costs and consequence of these two procedures is currently lacking.

Read the full abstract...
Background: 

Cataract is the leading cause of blindness in the world, and clinically significant astigmatism may affect up to approximately 20% of people undergoing cataract surgery. Pre-existing astigmatism in people undergoing cataract surgery may be treated, among other techniques, by placing corneal incisions near the limbus (limbal relaxing incisions or LRIs) or by toric intraocular lens (IOLs) specially designed to reduce or treat the effect of corneal astigmatism on unaided visual acuity.

Objectives: 

To assess the effects of toric IOLs compared with LRIs in the management of astigmatism during phacoemulsification cataract surgery.

Search strategy: 

We searched CENTRAL (which contains the Cochrane Eyes and Vision Trials Register; 2019, Issue 9); Ovid MEDLINE; Ovid Embase and four other databases. The date of the search was 27 September 2019.

Selection criteria: 

We included randomised controlled trials (RCTs) comparing toric IOLs with LRIs during phacoemulsification cataract surgery. 

Data collection and analysis: 

We used standard methods expected by Cochrane. We graded the certainty of the evidence using GRADE. Our primary outcome was the proportion of participants with postoperative residual refractive astigmatism of less than 0.50 dioptres (D) six months or more after surgery. We also collected data on mean residual refractive astigmatism. Secondary outcomes included: uncorrected distance visual acuity, vision-related quality of life, spectacle independence and adverse effects including postoperative lens rotation requiring re-alignment. To supplement the main systematic review assessing the effects of toric IOLs compared with LRIs in the management of astigmatism during phacoemulsification cataract surgery, we sought to identify economic evaluations on the subject.

Main results: 

We identified 10 relevant studies including 517 people (626 eyes). These studies took place in China (three studies), UK (three), Brazil (one), India (one), Italy (one) and Spain (one). The median age of participants was 71 years. The level of corneal astigmatism specified in the inclusion criteria of these studies ranged from 0.75 D to 3 D. A variety of toric IOLs were used in these studies, in all but one study, these were monofocal. Studies used three different nomograms to determine the size and placement of the LRI. Two studies did not specify this. None of the studies were at low risk of bias in all domains, but two studies were at low risk of bias in all domains except selective outcome reporting, which was unclear. The remaining studies were at a mixture of low, unclear or high risk of bias.

People receiving toric IOLs were probably more likely to achieve a postoperative residual refractive astigmatism of less than 0.5 D six months or more after surgery (risk ratio (RR) 1.40, 95% confidence interval (CI) 1.10 to 1.78; 5 RCTs, 262 eyes). We judged this to be moderate-certainty evidence, downgrading for risk of bias. In the included studies, approximately 500 eyes per 1000 achieved postoperative astigmatism less than 0.5 D in the LRI group compared with 700 per 1000 in the toric IOLs group. There was a small difference in residual astigmatism between the two groups, favouring toric IOLs (mean difference (MD) –0.32 D, 95% CI –0.48 to –0.15 D; 10 RCTs, 620 eyes). Although all studies favoured toric IOLs, the results of individual studies were inconsistent (range of effects –0.02 D to –0.71 D; I² = 89%). We considered this to be low-certainty evidence, downgrading for risk of bias and inconsistency. People receiving a toric IOL probably have a small improvement in visual acuity at six months or more after surgery compared to people receiving LRI, but the difference is small and probably clinically insignificant (MD –0.04 logMAR, 95% CI –0.07 to –0.02; 8 RCTs, 474 eyes; moderate-certainty evidence). Low-certainty evidence from one study of 40 people suggested little difference in vision-related quality of life measured using the Visual Function Index (VF-14) (MD –3.01, 95% CI –8.56 to 2.54). Two studies reported spectacle independence and suggested that people receiving toric IOLs may be more likely to be spectacle independent (RR 1.56, 95% CI 1.14 to 2.15; 100 people; low-certainty evidence). There were no cases of lens rotation requiring surgery (very low-certainty evidence). Five studies (320 eyes) commented on a range of other adverse effects including corneal oedema, endophthalmitis and corneal ectasia. All these studies reported that there were no adverse events with the exception of one study (40 eyes) where one participant in the LRI group had a central de-epithelisation which recovered over 10 days.

We found no economic studies that compared toric IOLs with LRIs.

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