Accuracy of Different Intraocular Lens Power Calculation Formulas in Patients with Shallow Anterior Chamber Cataracts: Meta-Analysis

Author: Li X, Yang L, Hai Y, Tan Q, Lan C, Liao X.

Geographical coverage: Not reported

Sector: Cataract surgery

Sub-sector: Intraocular lens

Equity focus: Not reported

Study population: Patients with cataract

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: The achievement of optimal visual outcomes after cataract surgery rely heavily on accurate ocular biometric measurements and precise intraocular lens (IOL) power calculations. The advancement in optical coherence biometry sector increases the accuracy of such measurements. Recently developed modern IOL formulas have evolved through generations, incorporating attributes like anterior chamber depth (ACD), axial length (AL), and corneal curvature. Among these, ACD is a highly recognized key factor that influences effective lens position (ELP) and refractive accuracy. However, shallow ACD presents unique challenges which often leads to higher postoperative refractive errors. Previous studies remained inconclusive on which IOL formulas perform best under these anatomical constraints.

Objective: To systematically compare the accuracy of different intraocular lens (IOL) power calculation formulas in patients with shallow anterior chamber cataracts.

Main findings: The review included 8 studies, involving 529 eyes, published between 2014 and 2020. The findings revealed that mean absolute error (MAE) of the Haigis formula was lower than that of the SRK/T formula (mean difference, MD: -0.86, 95% CI: -1.07 to -0.66, P < 0.00001), Hoffer Q formula (MD: -0.49, 95% CI: -0.52 to 1.50, P = 0.34), Holladay 1 formula (MD: -1.09, 95% CI: -1.58 to -0.61, P < 0.00001), and Barrett Universal II formula (MD: -0.49, 95% CI: -0.52 to 1.50, P = 0.34).  However, pairwise comparisons between other formulas showed no statistically significant differences. The ratio of the percentage of eyes with prediction errors within ±0.50 D was compared between formulas, but no statistically significant differences were found.

Methodology:  The searches were conducted in PubMed, Embase, Cochrane Library and Chinese databases (CNKI, Wanfang Data, VIP Database) to identify case-control studies conducted on patients with ACD ≤ 2.5 mm, undergoing routine cataract surgery and IOL implantation. The studies published in English and Chinese languages up to December 2020 were included if they used at least three target IOL power calculation formulas and measured ocular parameters using optical coherence biometry. The reference lists of included studies and previously published articles were also scanned to identify additional relevant publications.

Identified studies were screened to establish their eligibility for inclusion in this review. Two reviewers independently extracted the relevant data. Disagreements between the reviewers were resolved by contacting a third reviewer. The risk of bias and clinical applicability of the included studies were assessed using a quality assessment form adapted from the Cochrane Handbook. The findings were synthesised using a fixed or random-effects model meta-analysis depending on the heterogeneity, which was assessed using the Chi-square test and I² statistics. Sensitivity analysis and subgroup analysis were conducted to explore possible sources of heterogeneity, publication bias using a funnel plot.

Applicability/external validity: The review highlighted that the absence of randomised controlled trials, reliance on retrospective data, and small sample sizes for certain formulas (e.g., Barrett Universal II, Holladay 2) could limit the generalisability of the findings. Additionally, the study did not account for variations in IOL types or newer formulas, which may affect clinical outcomes. While the Haigis formula shows promise for shallow anterior chamber cases, the authors cautioned that the results should be interpreted carefully, emphasising the need for large-scale prospective studies to validate its applicability across diverse patient populations and advancing surgical technologies.

Geographic focus: The review did not apply any geographical limits. However, it did not report the geographical distribution of the included studies.

Summary of quality assessment: Overall, there is low confidence in the review’s conclusions. The searches were comprehensive. Inclusion and exclusion criteria were clearly defined, and two reviewers independently extracted data, with disagreements resolved through consultation with a third reviewer. The study quality was assessed using established tools. Characteristics of included studies were well-documented, meta-analyses were appropriately performed, and heterogeneity was addressed. However, a list of excluded studies was not provided. The review did not report checking the reference lists or contacting the authors/experts. English and Chinese language limits were applied, and findings were not reported by the risk of bias status. Additionally, the review did not specify the number of reviewers independently involved in screening.