With all the different progressive power lens (PPL) options available nowadays, it can be confusing when a patient enquires about them.
A patient might tell you that they tried varifocals many years ago and couldn’t get on with them, or that their next door neighbour said they couldn’t get on with them and so they are reluctant to try them.
The fact is, PPL designs have improved dramatically over the years, and there are only a handful of patients who are unable to tolerate them. However, careful patient selection together with accurate measurements are paramount in ensuring non tolerance cases are kept to a minimum.
In this last OA Corner of the year, we look at some of the relevant advantages and disadvantages of PPLs.
Pluses and minuses of PPLs
Advantages of PPLs include continuous vision from distance to near in one pair of spectacles, and no dividing lines visible on the lenses. The main disadvantages are the narrower visual areas when compared to either separate pairs of spectacles or bifocal lenses, and the areas of softer focus towards the periphery of the lenses.
This soft focus area is created by blending the surface to create a seamless lens with gradual power increases; but it can create unwanted aberrations that may be a problem for some wearers.
Early PPL designs fell broadly into two categories: hard and soft. Hard designs have a wider distance area, wider reading area, but a narrower intermediate area compared to a soft design. The soft focus areas are more pronounced in hard design lenses, which can make them more difficult to adapt to.
As technology improved, ultra-soft designs were developed, and these have wider intermediate areas with less pronounced soft focus areas. This makes them more suited to someone who needs prolonged intermediate use, such as for computer user.
Technology has now further improved, and bespoke PPLs are available. These lenses can be tailored to the individual patient, with the intention of providing the widest visual areas, making adaption much easier.
Traditional PPLs only required distance mono centre distances (CDs) and vertical heights, but modern bespoke lenses require additional measurements such as mono near CDs vertex distance, pantoscopic tilt, near working distance, face form angle and even the corridor length can be specified.
These individualised PPLs work especially well for patients with higher degrees of astigmatism, very narrow or very wide pupillary distances or frames that are outside the standard parameters, for example, a very wrapped frame or a frame with excessive or very little pantoscopic tilt.
With all PPLs, increasing the reading add narrows the reading area so this should be considered when there has been an increase in a patient’s reading add. The patient may be perfectly happy with a PPL design with the lower add but may not tolerate the same design and a higher add.
Similarly, if a patient is changed to a more expensive tailor-made design with an increased add, they may not notice the difference from the previous pair. Communication and explanation are key here, and if this is correctly explained to the patient at the time of dispensing, disappointment can be avoided.
Sue Deal FBDO R is a practising dispensing optician, ABDO College examiner, senior tutor and supervisor for dispensing opticians. She is also a practice visitor and external moderator for ABDO.
OA Corner Part 1: What makes a good OA
OA Corner Part 2: Communication
OA Corner Part 3: A question of strategies
OA Corner Part 4: Understanding bifocals
OA Corner Part 5: Our amazing eyes
OA Corner Part 6: Frame fittings basics
OA Corner Part 7: Frame styling factors
OA Corner Part 8: Single vision lens basics
OA Corner Part 9: Understanding spectacle prescriptions Part 1
OA Corner Part 10: Explaining spectacle prescriptions Part 2
OA Corner Part 11: Understanding glaucoma