Intraocular lens power calculation accuracy in patients with keratoconus: Network meta-analysis and systematic review

Abstract

Background: Accurate intraocular lens (IOL) calculation in eyes with keratoconus (KCN) poses significant challenges. While various formulas, including KCN-specific ones, have been investigated, the optimal calculation method remains inconclusive.

Methods: The study was pre-registered in PROSPERO (CRD42023483119). PubMed, Embase and CENTRAL electronic databases were systematically searched for studies comparing IOL power calculation formulas in eyes with KCN. The percentage of eyes with a prediction error (PE) within ±0.50 D and ±1.00 D, the mean PE and the mean absolute error (MAE) were compared using a random effect model in Bayesian network meta-analysis.

Results: Nine retrospective clinical studies were included, totalling 623 eyes and 25 calculation methods. The Barrett True-K formula for KCN with measured posterior cornea (BTK MPC) achieved the highest ranking for the percentage of PE within ±0.50 D and ±1.00 D, mean PE, and MAE, with surface under the cumulative ranking (SUCRA) of 95%, 95%, 97% and 95%, respectively. Subgroup analysis showed that for the predictability rates within ±0.50 D and ±1.00 D, the best ranking formulas were: Emmetropia Verifying Optical (EVO) (85%) and BTK MPC (78%), respectively, in mild KCN; BTK with predicted posterior cornea (PPC) (85%) and MPC (88%), respectively, in moderate KCN; and Kane KCN for both metrics in severe KCN (84% and 95%, respectively).

Conclusion: The BTK MPC formula ranked highest across various metrics, suggesting its superior accuracy for IOL calculations in KCN. The optimal formulas may differ based on KCN severity, with current evidence suggesting potential advantage of Kane KCN for severe cases.

Keywords: Kane keratoconus; cataract surgery; intraocular lens power calculation; keratoconusBarrett true K.

FIGURE 1

The flow diagram of the study selection.

FIGURE 2

Quality assessment of the included trials based on modified The Quality Assessment of Diagnostic Accuracy Studies‐2 (QUADAS‐2).

FIGURE 3

Overall network plots of all original comparisons for (A) the percentage of eyes within ±0.5 D and ± 1.0 D, (B) mean prediction error, and (C) mean absolute error. Each node represents one investigated formula. The size of the node is proportional to the number of eyes that were used to calculate IOL power with this formula. The edges represent direct comparisons, and the width of an edge is proportional to the number of studies. BTK MPC, Barrett true K for keratoconus with measured posterior cornea; BTK PPC, Barrett true K for keratoconus with predicted posterior cornea; BUII, Barrett Universal II; EVO, emmetropia verifying optical version 2.0; Holladay II KCN, Holladay II with keratoconus adjustment; Kane KCN, Kane keratoconus; RBF, radial basis function version 3.0; TK, total keratometry.

FIGURE 4

(A) Surface under the cumulative ranking curve (SUCRA) for all formulas, and (B) a forest plot of the network meta‐analysis results using the BTK MPC formula as reference, for the percentage of eyes with a prediction error within ±0.50 D. BTK MPC, Barrett true K for keratoconus with measured posterior cornea; BTK PPC, Barrett true K for keratoconus with predicted posterior cornea; BUII, Barrett Universal II; CrI, credible interval; EVO, emmetropia verifying optical version 2.0; Holladay II KCN, Holladay II with keratoconus adjustment; Kane KCN, Kane keratoconus; RBF, radial basis function version 3.0; TK, total keratometry.

FIGURE 5

(A) Surface under the cumulative ranking curve (SUCRA) for all formulas, and (B) a forest plot of the network meta‐analysis results using the BTK MPC formula as reference, for the percentage of eyes with a prediction error within ±1.00 D. BTK MPC, Barrett true K for keratoconus with measured posterior cornea; BTK PPC, Barrett true K for keratoconus with predicted posterior cornea; BUII, Barrett Universal II; CrI, credible interval; EVO, emmetropia verifying optical version 2.0; Holladay II KCN, Holladay II with keratoconus adjustment; Kane KCN, Kane keratoconus; RBF, radial basis function version 3.0; TK, total keratometry.

FIGURE 6

(A) Surface under the cumulative ranking curve (SUCRA) for all formulas, and (B) a forest plot of the network meta‐analysis results using the BTK MPC formula as reference, for the mean prediction error. BTK MPC, Barrett true K for keratoconus with measured posterior cornea; BTK PPC, Barrett true K for keratoconus with predicted posterior cornea; BUII, Barrett Universal II; CrI, credible interval; EVO, emmetropia verifying optical version 2.0; Holladay II KCN, Holladay II with keratoconus adjustment; Kane KCN, Kane keratoconus; RBF, radial basis function version 3.0; TK, total keratometry.

FIGURE 7

(A) Surface under the cumulative ranking curve (SUCRA) for all formulas, and (B) a forest plot of the network meta‐analysis results using the BTK MPC formula as reference, for the mean absolute error. BTK MPC, Barrett true K for keratoconus with measured posterior cornea; BTK PPC, Barrett true K for keratoconus with predicted posterior cornea; BUII, Barrett Universal II; CrI, credible interval; EVO, emmetropia verifying optical version 2.0; Holladay II KCN, Holladay II with keratoconus adjustment; Kane KCN, Kane keratoconus; RBF, radial basis function version 3.0; TK, total keratometry.