Intraocular lens power calculation formulas in high refractive errors….what to choose and when.

ABSTRACT

Background & Objectives: Before performing the cataract surgery high level of expertise and knowledge is required to fulfil the ever increasing demands of patients. This makes a surgeon carry out detailed evaluation of a case and formulate a ‘customized IOL’. Accurate IOL power calculation is the most important part of planning a cataract surgery. Most of the formula works well with normal axial length, but with high refractive errors, there are many discrepancies for selection of IOL formula. Methods: Study included 80 high myopic eyes divided into three groups and 20 high hypermetropic eyes divided into two groups according to various A scan formulas utilised. Post-operative spherical equivalent in relation to various formulas for all groups compared. Results: Performance of all 3 formulas in high myopic group showed SRK/T formula to be most accurate with smallest Mean Absolute Error (MAE) in all axial length subcategories above 24mm, followed by Haigis, and Holladay I respectively. In high hypermetropic patients, among 2 formulas, the lowest MAE was found with Hoffer-Q (-0.03D) compared to SRK/T (-0.96D) Interpretation & Conclusion: Erroneous IOL power calculation can spoil high quality results expected by patients in terms of post-operative vision in spite of excellent surgery.