Vivity extended depth of focus lens
Alcon claims Vivity as the first and only non-diffractive extended depth of focus IOL. It introduces what the company names as X-Wave technology or wavefront shaping technology combining two elements to simultaneously stretch and shift light without splitting light to give extended depth of focus (EDOF) vision to patients. These two surface transition elements are described to be in the central 2.2 mm of the IOL. The first raised plateau (around 1μ in height) delays a portion of the wavefront as it passes through the IOL, compared to the more advanced wavefront passing through the IOL outside of this zone (that passes through the base curvature of the lens). As a result the wavefront stretches as it collapses on the retina, with the delayed wavefront forming the image anterior to the retina, and the advanced wavefront travelling further to form the image at the far end of the extension.
The surface transition element 2 is a small change in curvature that shifts the wavefront to the anterior side of the retina to use all the available light.
Beyond this communication from Alcon, I have tried to understand the Vivity optics and explain in a simple way. Here is my impression, however to understand one may have to understand a physics term - 'phase difference'
In figure 1 we see a normal wave going up and down. The distance from A to E is completion of a cycle and therefore one wavelength. B,C,D are different parts of the wavelength that add up to form the complete wavelength.
In figure 2 you can see the phase differnce in the two waves. Both red and blue waves have the same
wavelength and the same amplitude (height of wave) and frequency. However, you can notice that the blue wave is slightly ahead of the red wave. This is what we call as phase difference. This is marked in dashed dots and called as phase difference between the two waves. This is key to understanding the Alcon Vivity lens with reference to the region marked in blue and labelled as (3)
Note: The above is an impression of the lens. Accuracy and correctness is not guranteed, but only indicative in nature.