Performance of IOL calculation formulas that use measured posterior corneal power in eyes following myopic laser vision correction

PURPOSE

To compare the predictive accuracy of the biometer-embedded Barrett True-K TK and new total corneal power methods of intraocular lens (IOL) power calculation in eyes with prior laser vision correction (LVC) for myopia.

SETTING

Academic clinical practice.

DESIGN

Retrospective case series.

METHODS

IOL power formulas were assessed using measurements from a swept-source optical coherence biometer. Refractive prediction errors were calculated for the Barrett True-K TK, EVO 2.0, Pearl-DGS, and HofferQST, which use both anterior and posterior corneal curvature measurements. These were compared with the Shammas, Haigis-L, Barrett True-K No History (NH), optical coherence tomography, and 4-formula average (AVG-4) on the ASCRS postrefractive calculator, and to the Holladay 1 and 2 with non linear axial length regressions (H1- and H2-NLR).

RESULTS

The study comprised 85 eyes from 85 patients. Only the Barrett True-K TK and EVO 2.0 had mean numerical errors that were not significantly different from 0. The EVO 2.0, Barrett True-K TK, Pearl-DGS, AVG-4, H2-NLR, and Barrett True-K NH were selected for further pairwise analysis. The Barrett True-K TK and EVO 2.0 demonstrated smaller root-mean-square absolute error compared with the Pearl-DGS, and the Barrett True-K TK also had a smaller mean absolute error than the Pearl-DGS.

CONCLUSIONS

The Barrett True-K TK and EVO 2.0 formulas had comparable performance to existing formulas in eyes with prior myopic LVC.

Effect of spherical aberration on visual acuity and depth of focus in pseudophakic eyes

PURPOSE

To assess the performance of 4 intraocular lenses (IOLs) in various spherical aberration (SA) conditions, using the VAO adaptive optics simulator.

SETTING

Cullen Eye Institute, Baylor College of Medicine, Houston, Texas.

DESIGN

Prospective case series.

METHODS

Distance-corrected visual acuities at distance (CDVA), intermediate (DCIVA), and near (DCNVA) were measured in 42 dilated pseudophakic eyes at baseline and with ocular SA ranging from -0.4 to +0.4 μm in increments of 0.2 μm (6.0-mm pupil). 4 IOL types were assessed: monofocal IOLs with zero-SA, enhanced-monofocal, extended depth-of-focus (EDOF), and continuous range-of-vision.

RESULTS

Compared with SA = 0 μm, significant changes (all P < .05) were: (1) zero-SA monofocal IOLs' DCNVA at high contrast improved by 0.13 logMAR with SA = -0.4 μm and worsened by 0.09 and 0.10 logMAR with SA = +0.2 and +0.4 μm, respectively. DCNVA at low contrast worsened by 0.09 logMAR with SA = +0.4 μm; and (2) with SA = -0.4 μm, the enhanced monofocal IOL lost 0.06 logMAR of CDVA at high contrast and gained 0.09 logMAR of DCNVA at low contrast. There were no significant changes from SA = 0 μm for EDOF and continuous range-of-vision IOLs.

CONCLUSIONS

Zero-SA and EDOF IOLs were the most and least sensitive to SA modulation, respectively. In perfect optical systems where all the optical elements are aligned, induction of targeted amounts of negative SA improved the depth of focus of some IOL types. No benefit was found with positive SA.

Efficacy of segmented axial length and artificial intelligence approaches to intraocular lens power calculation in short eyes

PURPOSE

In short eyes, to compare the predictive accuracy of newer intraocular lens (IOL) power calculation formulas using traditional and segmented axial length (AL) measurements.

SETTING

Cullen Eye Institute, Baylor College of Medicine, Houston, Texas and East Valley Ophthalmology, Mesa, Arizona.

DESIGN

Multi-center retrospective case series.

METHODS

Measurements from an optical biometer were collected in eyes with AL <22 mm. IOL power calculations were performed with 15 formulas using 2 AL values: (1) machine-reported traditional AL (Td-AL) and (2) segmented AL calculated with the Cooke-modified AL nomogram (CMAL). 1 AL method and 7 formulas were selected for pairwise analysis of mean absolute error (MAE) and root mean square absolute error (RMSAE).

RESULTS

The study comprised 278 eyes. Compared with the Td-AL, the CMAL produced hyperopic shifts without differences in RMSAE. The ZEISS AI IOL Calculator (ZEISS AI), K6, Kane, Hill-RBF, Pearl-DGS, EVO, and Barrett Universal II (Barrett) formulas with Td-AL were compared pairwise. The ZEISS AI demonstrated smaller MAE and RMSAE than the Barrett, Pearl-DGS, and Kane. K6 had a smaller RMSAE than the Barrett formula. In 73 eyes with shallow anterior chamber depth, the ZEISS AI and Kane had a smaller RMSAE than the Barrett.

CONCLUSIONS

ZEISS AI outperformed Barrett, Pearl-DGS, and Kane. The K6 formula outperformed some formulas in selected parameters. Across all formulas, use of a segmented AL did not improve refractive predictions.

Comparison of Keratoconus Specific to Standard IOL Formulas in Patients With Keratoconus Undergoing Cataract Surgery

PURPOSE

To assess the performance of multiple intraocular lens (IOL) formulas in eyes with keratoconus.

METHODS

Eyes with stable keratoconus scheduled for cataract surgery with biometry measurements on the Lenstar LS900 (Haag-Streit) were included. Prediction errors were calculated using 11 different formulas, including two with keratoconus modifiers. Primary outcomes compared standard deviations, mean and median numerical errors, and percentage of eyes within diopter (D) ranges across all eyes with subgroup analysis according to anterior keratometric values.

RESULTS

Sixty-eight eyes from 44 patients were identified. In eyes with keratometric values less than 50.00 D, prediction error standard deviations ranged from 0.680 to 0.857 D. Percentages of eyes within ±0.50 D of target ranged from 57.89% to 73.68% with no statistical differences among formulas. In eyes with a keratometric value of more than 50.00 D, prediction error standard deviations ranged from 1.849 to 2.349 D and were not statistically different with heteroscedastic analysis; percentages of eyes within ±0.50 D of target ranged from 0% to 18.18% with no statistical differences among formulas. Only keratoconus-specific formulas (Barrett-KC and Kane-KC) and the Wang-Koch axial length adjustment version of SRK/T resulted in median numerical errors not significantly different than 0, regardless of keratometric values.

CONCLUSIONS

In keratoconic eyes, IOL formulas are less accurate than in normal eyes and result in hyperopic refractive outcomes that increase with steeper keratometric values. Using keratoconus-specific formulas and the Wang-Koch axial length adjustment version of SRK/T for axial lengths of 25.2 mm or greater improved IOL power prediction accuracy compared to other formulas. [J Refract Surg. 2023;39(4):242-248.].