Varifocal lenses can cause a "swim effect", where peripheral vision can be slightly altered by the changes that occur at the edge of progressive lenses.
A varifocal must minimise swim effect, allowing the wearer to tolerate the lens, and enabling new wearers to adapt in the shortest time possible.
A big challenge in the design of a varifocal is to keep the field of vision as wide as possible, whilst also keeping the swim effect minimal. In general, higher quality varifocals have a wider field of vision.
Cheaper varifocals do not possess either of the above attributes, and after seeing so many customers struggle to adapt to cheaper varifocals, we only offer a mid-range, 'Standard' varifocal, and a very top of the range 'Premium' varifocal.