Proposed Topic (Most preferred): :
Clinical Safety and Quality Service I (Projects aiming to improve efficiency and effectiveness of care delivery to meet international standards)
Authors (including presenting author) :
Yau TH (1), Kam KW (1,2), Mok E (1, 2), Kwok S (1, 2), Tam WH (1), Wong YL (1), Yip WK (1,2), Young AL (1,2)
Affiliation :
(1) Department of Ophthalmology & Visual Sciences, Prince of Wales Hospital (2) Department of Ophthalmology & Visual Sciences, The Chinese University of Hong Kong
Introduction :
The American Society of Cataract and Refractive Surgery (ASCRS) calculator has been the gold standard in estimating the intraocular lens (IOL) power for patients with prior myopic refractive surgery and cataract. The method requires manual data entry and generates three suggested powers, minimum, average, and maximum. Newer biometers carry in-built formulas that directly indicate IOL powers without the need for calculation.
Objectives :
To compare the performance of the six formulas [Barrett True-K (IOL Master 700), Potvin-Hill (Pentacam AXL), Barrett True-K (Pentacam AXL) and the American Society of Cataract and Refractive Surgery (ASCRS) calculator (Average, Maximum, Minimum)] currently used at the Eye Centre of the Prince of Wales Hospital.
Methodology :
A retrospective study was performed on all cataract patients with prior refractive surgery between January, 2022 and September, 2023. Biometry was performed using two biometers, Pentacam AXL and IOL Master 700, and the predicted spherical equivalent (SE) was obtained using 6 different formulae. Patients’ post-operative SE was obtained by auto-refraction at one month. Outcome measures were the mean arithmetic error (ME) and mean absolute error (MAE) between the predicted and post-op SE of each formula.
Result & Outcome :
Fifteen eyes of 13 patients were analysed. Post-operative myopic shift is common with the ME of all formulas, suggesting an over-estimation of IOL power. Barret True K formula generated by the Pentacam AXL produced the smallest average ME of -0.39 Dioptre (D). Potvin-Hill (Pentacam AXL) produced the smallest average MAE of 0.52D. The average ME and MAE were the greatest for ASCRS Maximum, being -0.63 (D) and 0.76 (D) respectively. ASCRS Minimum achieved the highest number of patients with a ME of within 0.25D (27%) and 0.5D (67%) amongst all formulae. Both Barrett True K and Potvin Hill formulae of the Pentacam AXL achieved the highest number of patients with a ME of within 1.0D (90%) In cataract patients with prior myopic refractive surgery, post-operative myopic shift is common when using the six existing formulas to predict spherical equivalent. The mean error achieved by all six formulae were comparable, with the ASCRS Minimum achieving the highest accuracy followed by the Pentacam AXL formulae.
