A comparative study of three presbyopia-correcting lenses demonstrates that aspheric lenses offer superior performance over other designs.
Upgrade led to a second study
Soon after, the SN60D3 model was upgraded to the similar but aspheric IOL model SN6AD3, which provided better near and far visual acuity (VA) and higher contrast sensitivity. The results of a direct comparison between the spherical and aspheric lens designs were presented at the Ocular Surgery News Meeting in Naples in May 2008 by Dr Eduard Haefliger. We compared patient experience with the two lenses: 40 eyes received the SN60D3 model (evaluated 18 months after surgery) and 12 eyes received the aspheric SN6AD3 model (analysed three to six months after surgery). We concluded that patient satisfaction was higher with the aspheric SN6AD3, due to higher VA, better contrast sensitivity, and lower perception of glare.
With the advent of a new ReSTOR IOL that incorporates a lower near addition power, we were able to clinically compare these three different but similar lenses. The new lens, model SN6AD1, has +3.0 dioptres of add power at the lens plane, equal to approximately +2.5 dioptres at the spectacle plane. Visual performance and patient satisfaction (for 40 eyes that received the SN6AD1 model) were analysed 3 to 6 months after surgery. The cumulative results for all three IOL models were presented at the 2008 ESCRS meeting in Berlin.
The similarities and differences
The Alcon AcrySof ReSTOR model SN6AD1 (+3 D model) utilizes the same platform as the SN6AD3 (+4 D model), with an identical asphericity, energy distribution profile and shape factor. However, the near add power has been modified by changing the number of diffractive steps from 12 (with the SN6AD3) to 9 (with the SN6AD1), while the central diffractive region was maintained at 3.6 mm. Like the SN6AD3, the SN6AD1 has an apodized optic of concentric steps. Apodization is the proprietary gradual reduction in the step height towards the periphery of the diffractive region, which reduces the amount of light directed to the near focus as the pupil enlarges. This reduces the potential for visual disturbances in low-light conditions such as night driving.
Visual acuity and defocus curve