ACCURACY OF SUM-OF-SEGMENTS AXIAL LENGTH OPTIMIZED IOL POWER CALCULATION FORMULAS USING SUM-OF-SEGMENTS BIOMETRY
Published 2024 - 28th ESCRS Winter Meeting
Reference: FP05 | Type: Submission | DOI: 10.82333/nej4-4j52
Authors: Carlos Nogueira* 1 , Telmo Cortinhal 1 , Inês Figueiredo 1 , Nuno Gouveia 1 , Miguel Raimundo 2 , Conceição Lobo 2 , Joaquim Murta 2
1Ophthalmology,Centro Hospitalar e Universitário de Coimbra (CHUC), Coimbra, Portugal,Coimbra,Portugal, 2Ophthalmology,Centro Hospitalar e Universitário de Coimbra (CHUC), Coimbra, Portugal,Coimbra,Portugal;Clinical Academic Center of Coimbra,Coimbra,Portugal;Coimbra Institute for Clinical and Biomedical Research,Coimbra,Portugal;Faculty of Medicine, University of Coimbra,Coimbra,Portugal
Purpose
Sum-of-segments (SOS) axial length (AL) is a new way of measuring axial length (AL) through the composite sum of the optical path length of each segment of the eye using a specific refractive index. A new commercially available swept-source OCT biometer is able to measure SOS-AL and optimized formulas have been developed, though evidence on their influence on biometric outcomes is still accumulating. In this study we aim to compare the performance of sum-of-segments optimized Barrett Universal II and EVO formulas with their standard versions, using a SOS biometer.
Setting
Academic University Hospital
Methods
Retrospective consecutive study of eyes that underwent cataract surgery with a monofocal IOL (Alcon SN60AT). A swep-source biometer which measures a SOS AL was used. The post-operative spherical equivalent (SE) for the IOL was estimated using the Barrett True Axial Length (BTAL), the standard Barrett Universal II formula (BUII), the EVO formula optimized for SOS AL (EVOTAL) and the standard EVO formula (EVO). The post-operative SE was obtained by subjective refraction at 6-12 weeks. Subgroups by AL were defined: small (<22.0mm), medium (22.0m-24.5 mm) and long eyes (>24.50 mm). Outcomes included the median absolute prediction error (MedAE) and the proportion of eyes within 0.25, 0.50 and 1.00 diopters (D) of the pre-operative prediction.
Results
We included 1315 eyes with mean AL 23.36±1.06mm (range 20.87-29.22 mm). The AE in the whole sample was significantly lower using the BTAL formula compared to the BUII (MedAE 0.276D vs 0.281D, p=0.038), but did not differ when using the EVOTAL over the EVO. In small eyes (n=86), predictions with the BTAL further improved (MedAE 0.235 vs 0.276,p=0.004), with improved predictions within 0.25D (45.2% vs 43.8%) 0.50d (81.4% vs 75.6%) and 1.00D (97.7% vs 100%). In long eyes (n=135), the BTAL did not significantly improve results while the EVOTAL significantly outperformed the standard EVO formula (MedAE 0.329 vs 0.350, p=0.018), with improved predictions within 0.25 (37.8% vs 36.3%), 0.50D (73.3% vs 68.9%) and the same within 1.00D (98.5%).
Conclusion
In a large sample of eyes whose biometry was acquired using a SOS biometer, the BTAL formula significantly improved predictions over the standard BUII formula, particularly in small eyes. Conversely, the SOS optimized EVO formula improved predictions over the standard formula only for long eyes, where no beneficial effect for the BTAL was seen. SOS optimized formulas seem promising to improve the performance of modern IOL power calculation formulas in the extremes of axial length.