Small-pupil versus multifocal strategies for expanding depth of focus of presbyopic eyes.

PURPOSE: To compare the visually weighted image quality and depth of focus achieved with small-pupil and multifocal strategies for expanding depth of focus of presbyopic or pseudophakic eyes.

SETTING

School of Optometry, Indiana University, Bloomington, USA.

DESIGN

Computational modeling.

METHODS

The visual Strehl ratio was computed from monochromatic optical transfer functions over a wide range of primary spherical aberration and defocus levels for pupil diameters ranging from 1.0 mm to 7.0 mm under high photopic light levels (retinal illuminance >900 trolands) and mesopic light levels (2 candelas/m2).

RESULTS

Pupil miosis and added spherical aberration were effective at reducing the impact of spherical defocus. With high light levels at which Weber's law makes neural contrast sensitivity independent of retinal illuminance, small pupils (eg, 1.0 to 3.0 mm) generated higher peak image quality and more effective expansion of depth of focus than the small-pupil multifocal model. However, under low light levels at which the reduced retinal illuminance associated with pupil miosis lowered neural contrast sensitivity, the peak image quality was lower with small pupils (1.0 to 1.5 mm) at all aberration levels. Large pupils and high levels of spherical aberration were most effective at expanding the depth of focus under mesopic light levels.

CONCLUSIONS

When reductions in retinal illuminance created by pupil miosis have no effect on neural contrast sensitivity, small pupils produced higher image quality and larger depth of focus than multifocal optics and large pupils. In general, the reverse was true under mesopic light conditions.