In 2007, we presented a study at the Congress of the German Ophthalmic Surgeons in Nurnberg, showing the functional vision of patients implanted with the AcrySof ReSTOR multifocal intraocular lens model SN60D3. The SN60D3 provides +4.0 dioptres of add power at the lens plane, equal to approximately +3.2 dioptres at the spectacle plane. That first generation of Alcon's ReSTOR family showed good visual function and high patient satisfaction.

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.

Third IOL release

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

Figure 1: The SN6AD1 (+3 D) provided visual acuity that was superior to the other two IOLs at all distances, except at 30 cm: that distance represents the near focus point of the SN6AD3 lens. The VA was slightly better with the SN6AD3.

We measured uncorrected visual acuity (UCVA) and best corrected visual acuity (BCVA) at distances from 30 cm to 70 cm (in 10 cm steps) and at six metres. Due to enhanced postoperative management and the increased optical quality of the aspheric designs, the SN6AD3 (+4 D) and SN6AD1 (+3 D) lenses performed better than the spherical SN60D3, as shown in Figure 1. Figure 1 also shows that the SN6AD1 (+3 D) provided visual acuity that was superior to the other two IOLs at all distances, except at 30 cm – that distance represents the near focus point of the SN6AD3 lens. While the VA was slightly better with the SN6AD3, average near vision was 0.9 or better for all three lenses at this distance.