These are different to Bifocal Lenses because they provide a Gradient in prescription rather than two very different prescriptions side by side.
They are generally set out in the same format as Bifocal with the highest Short Sightedness Prescription at the top of the lens, gradually decreasing until it reaches the highest Long Sighted Vision at the bottom of the lens.
These are often offered in place of Bifocal Lenses.
There are many different advantages of this type of lens.
Firstly, the wearer can choose the exact type of vision if they so choose by tilting their eye through a specific part of the lens.
However, this is normally not needed as the prescriptions are placed where the wearer will need them the most and thus any manual focusing is much easier.
Secondly, there is no "jumping "from images as there is a gradient of prescription rather than a sudden change as there is in Bifocal Lenses.
As it is obvious on Bifocal Lenses where the two different prescriptions are, the Varifocal Lenses do not have this and thus do not carry any associated stigmatism with this image, making the wearer more confident in themself.
However, there can be some distortion or blurring due to the very nature of the glasses; this does vary however with different qualities of lens.
This is effect is also worse when the prescriptions are higher, Clinicians have found that the wearer can get used to this effect and thus encourage that this lens type is started early and thus when eyes worsen in old age, the eye is already used to this effect.
There can sometimes also be a problem in peripheral vision and thus for some workers it is recommended that an Occupational Progressive Lens is used instead, also known as an Office Lens or Extended Reading Lens.
These are often more expensive as well than Bifocal Lenses.
These require very specific fitting to ensure that the viewer does not have narrow vision and will not to always be tilting their head to see clearly.
When at the opticians, the Clinician will spend much time measuring you for fitting and will ask a large range of questions to ensure that you are getting the best for your eyes.
This is because different lenses have different prescriptions, heights or even prices.