In some eyes, aberrometric measurements of the refractive error can differ by more than 1 diopter from standard subjective refraction. We aim to understand the reasons for these discrepancies and to study the role of both amplitude (irregular or inhomogeneous pupil transmission) and phase (aberrations) of the wavefront.
The spherical equivalent was measured by different subjective, objective, and aberrometric methods in a population of 177 eyes. We first analyzed the degree of correlation between the outcomes of the different methods. Then we analyzed cases showing the highest discrepancies (>1 diopter) between subjective and aberrometric spherical equivalent. The refractive error sensing method was generalized and applied here to include the effect of inhomogeneous pupil transmittance (Stiles-Crawford effect) and irregular pupil shapes on refractive error.
Objective and aberrometric methods showed a strong correlation with subjective methods (R2 > 0.89 in all cases). However, individual data points may show large discrepancies. Several eyes with discrepancies of 1 D or even 2 D usually presented higher values of higher-order aberration (mainly coma and/or spherical aberration) than average, which may cause these eyes to have a natural bifocal (or even multifocal) optical performance. Refractive error sensing analysis suggests that this multifocal performance could explain the high objective-subjective discrepancies found in these eyes. Nevertheless, the Stiles-Crawford effect (or irregular pupils) can substantially modify the energy distribution, tending to minimize multifocal effects, thus minimizing discrepancies between aberrometric and subjective refraction.
Discrepancies between aberrometric and subjective refraction may appear in aberrated eyes when aberrometric methods ignore the impact of the wavefront amplitude (inhomogeneous or irregular pupil transmittance.) The generalized refractive error sensing proposed here seems promising and able to provide a reliable clinical refraction in monofocal and multifocal eyes.