Intraocular Lens Power Calculation After Laser Refractive Surgery: A Meta-Analysis

Author: Chen H, Chen X, Wang H, Fang Z, Yao K. 

Geographical coverage: America, Europe, China, and Egypt

Sector: Refractive 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

Cataract accounts for 51% of global blindness. Advancements in cataract surgery and intraocular lens (IOL) technology have raised expectations for excellent refractive outcomes. However, accurate IOL power calculation remains challenging in patients with a history of laser refractive surgeries such as photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK). These eyes often display residual refractive errors due to altered corneal properties, making standard formulas less reliable. Errors may arise from instrument limitations, changes in refractive index, and formula inaccuracies. Over time, IOL formulas have evolved through multiple generations, each aiming to improve precision. Still, no universally accepted formula exists for post-refractive surgery eyes, underlining the need for comparative evaluations of the available methods.

Objective

To compare the accuracy of different intraocular lens (IOL) power calculation formulas following laser refractive surgery (PRK or LASIK).

Main findings

The review included 10 studies (267 eyes): seven comparative cohort studies and three prospective case series. Of the included studies, six were conducted in America, two in Europe, one in China, and one in Egypt. The mean age of participants ranged from 28 to 61 years, axial length (AL) ranged from 25 to 30 mm, and follow-up duration ranged from one month to two years. All studies were assessed as having a low risk of bias.

The analysis found no statistically significant difference in predictive accuracy between the Haigis-L formula and Shammas-PL (mean absolute error [MAE] difference: 0.16 D, 95% CI: -0.02 to 0.35, p = 0.09), or between Haigis-L and other formulas such as Hoffer Q, SRK/T, and Holladay 1. Subgroup analyses, however, revealed notable differences depending on the calculation method. For instance, in the double-K subgroup, Holladay 1 demonstrated significantly lower MAE compared to SRK/T (weighted mean difference [WMD]: 0.22 D, 95% CI: 0.03 to 0.42, p = 0.03). In the single-K subgroup, Hoffer Q outperformed SRK/T with a significantly lower MAE (WMD: 0.59 D, 95% CI: 0.25 to 0.93, p = 0.0006), though no significant difference was found in the double-K subgroup (p = 0.50).

Similarly, when comparing Holladay 1 and Hoffer Q, the single-K subgroup favoured Hoffer Q (WMD: 0.26 D, 95% CI: 0.01 to 0.51, p = 0.04), while the double-K subgroup showed no significant difference. These findings suggest that the double-K method may improve predictive accuracy by incorporating both pre- and post-refractive keratometry values. Although Haigis-L showed no significant difference in accuracy when compared to other formulas, its mean error was often more favourable, especially in comparisons with Hoffer Q. Overall, the results highlight the importance of choosing the appropriate formula and calculation method based on the availability of historical corneal data.

Methodology

Searches were conducted in PubMed and Embase up to March 2019 to identify cohort studies and case series comparing IOL calculation formulas. No language restrictions were applied. Two reviewers independently screened and critically appraised the studies using the Newcastle-Ottawa Scale. Disagreements were resolved through discussion or by consulting a third reviewer. One reviewer extracted data and a second reviewer checked it for accuracy. Meta-analyses were performed using fixed- or random-effects models depending on heterogeneity. Heterogeneity was assessed using I² statistics, publication bias via funnel plot, and sensitivity analyses were used to evaluate the robustness of findings.

Applicability/external validity

The review acknowledged that the number of included studies was small, and some comparisons were based on a single study, limiting the robustness of subgroup analyses. Differences in measurement tools and corneal imaging techniques introduced heterogeneity but also reflected real-world clinical variation.

Geographic focus

The review did not apply any geographical limits. The included studies were conducted in America, Europe, China, and Egypt.

Summary of quality assessment

Overall, there is medium confidence in the study’s conclusions. The searches were comprehensive and performed in PubMed and Embase with no language restrictions. Inclusion and exclusion criteria were clearly stated. Two reviewers independently screened and assessed study quality using validated tools. Disagreements were resolved by discussion or a third reviewer. Meta-analyses were appropriately conducted and heterogeneity addressed. However, the review did not list excluded studies or report grey literature searches, reference list checks, or author contact attempts.