Defocus curves: focusing on factors influencing assessment

Defocus curve assessment is used to emulate defocus over a range of distances and is a valuable tool that is used to differentiate the performance of presbyopia-correcting intraocular lenses. However, defocus curves are limited by a lack of standardization, and multiple factors can affect their generation and interpretation. This review discusses key factors that influence the assessment of defocus curves, including pupil size, level of contrast, sphere vs cylinder defocus, viewing distance, monocular vs binocular assessment, use of Snellen vs logMAR charts, and diopter range and step size. Moreover, different methods to analyze defocus curves, including the direct comparison method, range-of-focus analysis, and area under the curve analysis, can affect result interpretation. A good understanding of these factors and standardization of the methodology are important to ensure optimal cross-study comparisons.