Accuracy of intraocular lens power calculation formulas in pediatric cataract patients: A systematic review and meta-analysis

Author: Zhong Y, Yu Y, Li J, Lu B, Li S, Zhu Y.

Geographical coverage: United States, China, Korea, Nepal, India and Canada

Sector: Diagnosis

Sub-sector: Accuracy, Intraocular lens

Equity focus: Not reported

Study population: Paediatric patients with cataract

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: Paediatric cataracts are a major cause of childhood blindness worldwide, often needing early surgery with intraocular lens (IOL) implantation. Precise refractive outcomes in children are challenging due to rapid eye growth, smaller anatomy, and difficulty in getting accurate measurements. Most IOL power formulas are designed for adults, raising concerns about their use in children. Newer formulas developed for adults may not be effective for children, as past studies show inconsistent results. This underscores the need for a thorough comparison of IOL formulas specifically for paediatric patients.

Objectives: To compare the accuracy of the IOL power calculation formulas used for paediatric cataract patients.

Main findings: A total of 12 studies (1647 eyes) were included in the meta-analysis. Among these, 10 were retrospective cohort studies, one was a prospective cohort study, and one was a randomised controlled trial (RCT). Five of the 12 included studies were conducted in the United States, three in China, three in other Asian countries, and one in Canada. The methodological quality of all included studies was assessed as having a low risk of bias.

The meta-analysis conducted by the authors compared the accuracy of five intraocular lens (IOL) power calculation formulas: Holladay 1, Holladay 2, Hoffer Q, SRK/T, and SRK II. All the formulas exhibited some degree of absolute prediction error (APE) in pediatric eyes. Holladay 1 showed the smallest APE (0.97; 95% CI: 0.92–1.03), followed by Holladay 2 (APE: 1.05; 95% CI: 0.94–1.17) and Hoffer Q (APE: 1.05; 95% CI: 1.00–1.11). SRK II had the largest APE (1.34; 95% CI: 1.28–1.41).

For patients with an axial length (AL) less than 22mm, authors found that SRK/T resulted in a significantly smaller APE than SRK II (mean difference [MD]: −0.37, 95% CI: −0.63 to −0.12). For patients younger than 24 months, authors note that SRK/T had a significantly smaller APE than Hoffer Q (MD: −0.28, 95% CI: −0.51 to −0.06). For patients aged between 24 and 60 months, SRK/T presented a significantly smaller APE than Holladay 2 (MD: −0.60, 95% CI: −0.93 to −0.26). In summary, the meta-analysis displayed high variability of refractive status among paediatric patients. SRK/T showed a relatively smaller postoperative refractive error under certain conditions.

Methodology: Authors searched PubMed, Embase, and Web of Science to identify cohort studies conducted on paediatric cataract patients who underwent cataract extraction and primary posterior chamber IOL implantation, compared at least two types of the target IOL power calculation formula, and reported either prediction error (PE) or APE values (with 95% CI). The studies published in English up to April 2020 were included in this review. Reference lists of the included studies were also scanned to identify additional relevant publications.

Two reviewers independently screened the articles. Discrepancies between the reviewers were resolved through discussion. Relevant data was extracted in a standardised data collection form. The methodological quality of the included studies was assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2). The findings were synthesised using random-effects model meta-analysis. Sensitivity analysis was performed to determine the effect of a single study on overall results. Heterogeneity was assessed using I² statistics, and publication bias was assessed using a funnel plot and Egger’s test.

Applicability/external validity: The review did not explicitly address the applicability or external validity of its findings. Nonetheless, it acknowledged several factors that may affect generalisability, including the extensive age range of paediatric patients (1.1 to 216 months), variability in axial lengths and ocular development, and the inherent challenges in measuring paediatric ocular parameters. Additionally, the authors observed that most of the included studies were retrospective in nature and susceptible to selection bias and confounding factors. Due to the substantial variability within the study sample, the authors were unable to reach a definitive conclusion for the entire sample. However, subgroup analyses based on age and axial length yielded significant and informative results.

Geographic focus: The included studies were conducted in the United States, Canada, and Asia (China, Korea, Nepal, and India).

Summary of quality assessment: Overall, there is low confidence in the review’s conclusions. Literature searches were limited to identifying articles published in the English language only, and it is unclear how many reviewers independently performed the data extraction process.