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Observational Study
. 2019 Nov 12;19(1):222.
doi: 10.1186/s12886-019-1226-7.

T2 formula in a highly myopic population, comparison with other methods and description of an improved approach for estimating corneal height

Carlos Alberto Idrobo-Robalino  1 , Gisella Santaella  2 , Ángela María Gutiérrez  2
Affiliations
Observational Study

T2 formula in a highly myopic population, comparison with other methods and description of an improved approach for estimating corneal height

Carlos Alberto Idrobo-Robalino et al. BMC Ophthalmol. .

Abstract

Background: To determine the accuracy of the T2 formula as applied to highly myopic eyes, to compare the T2 formula to the SRK/T and Holladay 1 formulas, and to describe possible ways to improve the estimation of corneal height and prediction error in two settings, the Hadassah Hospital, Ophthalmology Department, Jerusalem, Israel and Clínica Barraquer, Bogotá, Colombia.

Methods: In this retrospective case series, optical biometer measurements were taken for 63 highly myopic patients (> 25 mm) undergoing uneventful crystalline lens phacoemulsification and insertion of an acrylic intraocular lens. Prediction errors were obtained, with estimations of ±0.50 D, ± 1.00 D, and greater than ±2.00 D. A method to improve the corneal height calculation is described.

Results: The SRK/T formula (mean absolute error [MAE] = 0.418; median absolute error [MedAE] = 0.352) was the most accurate, followed by the T2 (MAE = 0.435; MedAE = 0.381) and Holladay 1 (MAE = 0.455; MedAE = 0.389) formulas. Both the SRK/T and T2 formulas overestimated corneal height, but values were higher with the T2 formula. Corneal height was more precisely estimated using an alternative method that, when combined with axial length optimization, resulted in lower MAE (0.425) and MedAE (0.365) values than when applying the T2 formula alone.

Conclusions: The T2 formula seems to be less accurate than the SRK/T formula in highly myopic eyes. An improved corneal height estimation method is described for the the T2 formula.

Keywords: Cataract surgery; Corneal height estimation; High myopia; Intraocular lens calculation; T2 formula.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig 1
Fig 1
Median and Mean Absolute Error of the T2, SRK/T and Holladay 1 formulas Abbreviations: MAE: Mean Absolute Error; MedAE: Median Absolute Error; T2: T2 formula; SRK/T: SRK/T formula, n=63
Fig 2
Fig 2
Box plot of Corneal Height estimations using SRK/T, T2 and the alternative Corneal Height method described. Abbreviations: HSRK/T: Corneal Height estimation using steps 2 to 4 of the SRK/T formula; H2: Corneal height estimation using equation number 1 for H described by Sheard et al. [6] and programed in the T2 formula. H2.2: Corneal height estimation using equation number 2 for H described by Sheard et al. [6] and applied in the present work. n = 63
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