When is refraction stable following routine cataract surgery? A systematic review and meta-analysis

Methodological quality of the review: Medium confidence

Authors: Charlesworth E, Alderson AJ, de Juan V, Elliott DB.

Region: United States of America (USA), and one each in the United Kingdom (UK), Germany, Spain, Japan, Denmark, Italy and Turkey

Sector: Biomedical

Subsector: Treatment

Equity focus: Not stated

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:
Cataract surgery is the most common surgery performed in the UK, with approximately 400,000 surgeries per year; between 2015-2035 this is anticipated to increase by 50%. There appear to be substantial advantages in providing new glasses quicker than 4-6 weeks. A delay between surgery and the prescribing of new spectacles has been shown not only to be inconvenient to the patient, but may also have a negative effect on their quality of life during the postoperative period.

Objectives:
To investigate when refraction is stable following routine cataract surgery implanting monofocal intraocular lenses.

Main findings:
A total of nine studies were included in the review by the authors. Three studies gave no details of how refraction was measured. Five of the studies attempted to determine when refraction was stable following cataract surgery. Two studies compared standard phacoemulsification with femtosecond laser-assisted cataract surgery. The remaining two studies assessed IOL selection choice. Two studies were conducted in the USA, and one each in the UK, Germany, Spain, Japan, Denmark, Italy and Turkey.

Four studies were omitted from either the 1-week vs 4-weeks meta-analysis or 2-week vs 4-weeks meta-analysis. They were still included in the systematic review as part of a qualitative analysis. Overall, five studies were included in the meta-analysis as they compared refraction at 1-week vs 4-weeks, and included the relevant SE (three), spherical (one) and cylindrical (three) data.

Out of the four studies that were not included in the meta-analysis, authors noted that one study concluded that spectacles could be prescribed 2 weeks following cataract surgery; and three studies concluded refraction was stable after 1 week.

Based on the studies included in the meta-analysis, authors observed no evidence of time having an effect on refraction, with I² values showing high homogeneity across all studies. The ES, Q statistics and I² statistics for SE data were ES=-0.01 (95% CIs of -0.12 and 0.10; Z = 0.13 P=0.90), Q=0.03 (P=0.99), I²=0%; spherical data: 0.00 (95% CIs of -0.17 and 0.17; Z=0.0 P=1.0); cylindrical data: ES=+0.06 (95% CIs of -0.05 and 0.17; Z=1.02 P=0.31), Q=1.18 (P=0.55) and I²=0%.

The estimated statistical power of the meta-analysis observed by the authors was 99.2% for SE (three studies of mean N=64), 81.8% for sphere (one study, N=100) and 99.4% for cylinder (three studies of mean N=70).

A meta-analysis for 2-weeks vs 4-weeks was also conducted and authors reported consistent results with the 1-week vs 4-weeks meta-analysis, although there was only one set of data for each of spherical, SE and cylinder, so these are not shown.

Overall, authors concluded, based on the findings of this review, that refraction was stable sooner than the current guidelines of 4-6 weeks following surgery.

Methodology:
Medline, CINAHL, AMED, Web of Science, Embase and the Cochrane Library were searched up to 1 August, 2019. In addition, unpublished literature was searched using OpenGrey (www.opengrey.eu). The study’s inclusion criteria were:

• Adults undergoing routine, uncomplicated cataract surgery for age-related cataracts.
• Manual cataract surgery via clear corneal incision.
• Cataract aspirated using phacoemulsification.
• Sutures not required to close the corneal incision.
• Monofocal IOLs implanted.
• Refraction measured within 1 week of surgery, either subjectively or objectively, and at regular intervals until 4 weeks after surgery.
• Conducted in an upper-middle-income or high-income economic country (defined by the World Bank as a Gross National Income (GNI) per capita between $3,995 and $12,376).
• Printed in English.

Title and abstracts were screened by the two reviewers to assess if they met the criteria. Data extraction forms were created using the Critical Appraisal Skills Programme (CASP) quality assessment tool guidelines. The quality of the papers was evaluated using the first eight items (those relating to observational and non-comparative studies) of the Methodological Index for Non- Randomised Studies (MINORS).

Statistical analysis of included studies involved extracting mean refraction data and standard deviation (SD) and number of participants. Refraction data was compared at 1-week vs 4-weeks, and 2-weeks vs 4-weeks. Effect sizes (ES) were derived from each study using the mean, SD and N already extracted using the procedures outlined by Hedges and Olkin. The overall ES was determined by considering the ES of all the studies using a weighted fixed effects model. The contribution of each study ES to the overall weighted ES was determined by the inverse variance-weighted estimation as described by Hedges and Olkin. Heterogeneity among studies were analysed using the I² and Cochran’s Q test.

Applicability/external validity:
In most studies, cataract surgery was only conducted at one hospital, with one exception. Therefore, authors noted that this makes it difficult to determine whether the patients at each of these hospitals were representative of the general population. Depending on health care systems in different countries and areas, patients may have to reach a certain level of visual acuity (VA) or cataract density before receiving surgery. Authors also observed that very few studies discussed how many patients were excluded due to the tight inclusion and exclusion criteria, making it difficult to determine the applicability of findings to the general population.

The authors also noted some limitations which need to be considered when considering external validity of: the meta-analysis of the cylindrical data may be limited, in that the cylinder data is skewed, yet were incorporated into the meta-analysis from means and standard deviations (i.e. assuming a normal distribution). The meta-analyses were also limited by two factors: the relatively small number of studies and patients, with only one study and an N of 100 for sphere only data. The results are only applicable for the surgical technique and incision sizes used.

Geographic focus:
Authors did not discuss the applicability of findings to low and middle income countries.

Summary of quality assessment:
Overall, medium confidence was attributed to the effects of this study. Although authors conducted through searches of the literature, restrictions were applied to include studies written in English only. Appropriate methods were used to assess the quality of included studies and although authors do provide a summary of risk of bias, assessment against each criterion was not reported.