Near vision with a monofocal aspheric IOL

October 15, 2008

In the current era of presbyopia-correcting IOLs, toric IOLs, and aspheric IOL technology, the practice milieu is changing.

Key Points

Multiple peer-reviewed, prospective, randomized scientific publications have demonstrated reduction or elimination of spherical aberration with the Tecnis modified prolate IOL when compared with a variety of spherical IOLs.4-13 Data show that the mean spherical aberration in the eyes with the Tecnis IOL implanted is, in the words approved by the FDA, "not different from zero." Studies have also documented superior functional vision with the Tecnis IOL. Subjects in the FDA-monitored randomized double-masked night-driving simulation study of the Tecnis IOL performed functionally better in 20 of 24 driving conditions (and statistically better in 10 conditions) when using best spectacle correction with the eye with the Tecnis IOL implanted, as compared with best spectacle correction with the eye with the AcrySof spherical IOL implanted.3 Data from the night-driving simulation showed a significant correlation between reduction of spherical aberration and detection distance for the pedestrian target under rural conditions with glare (the most difficult target to discern).

More recently, peer-reviewed published clinical studies also have supported superior functional vision and reduction of spherical aberration with the AcrySof IQ when compared with spherical IOLs.14-17 In fact, the optical advantages of aspheric IOL technology have become well established, although some controversy remains in the areas of functional benefit as it relates to pupil size, IOL decentration, customization, and depth of focus.18 Some studies have shown little or no benefit of aspheric IOLs with smaller pupils,13,14 whereas one laboratory study showed that the SofPort AO provides better optical quality than either a negatively aspheric or a spherical IOL under conditions of significant decentration.19

Depth of focus

Regarding depth of focus, Rocha et al. have shown diminished distance-corrected near visual acuity, a surrogate measure for depth of focus, with the AcrySof IQ aspheric IOL as compared with the AcrySof SN60AT spherical IOL.17 The impact of the reduction or elimination of spherical aberration on depth of focus has been addressed by other researchers but remains unsettled.20-22 The primary outcomes of the study by Rocha et al.17 are the differences in near and intermediate vision. These differences, however, in reality are rather small. To give an idea of the magnitude of these differences, translated to the Snellen and Jaeger scales with which most clinicians are more familiar, the mean distance-corrected near visual acuity is 20/63 (J8) for the IQ, 20/50 (J6) for the SN60AT, and 20/60 (J7) for the AR40. The means, therefore, are only one line apart in either direction. The mean distance-corrected intermediate visual acuity is 20/40 for the SN60AT and 20/50 for both the IQ and the AR40. Thus, the mean values are relatively close; the significant p values occur because the standard deviations are relatively small. The question becomes the clinical significance of J7 versus J8 near vision-neither is adequate, for example, to read this article.