Blessing or Curse
When progressive lenses were first introduced in the 1960s they were promoted as providing a more natural form of vision which would replace bifocals and trifocals. It soon became apparent that this was not the case. Indiscriminate use of the lenses led to a very high rejection rate. Furthermore, zones of distorted vision, which are inherent in all progressive lenses, were far more problematic in earlier designs.
These distortion zones severely limited the use of this type of lens. For example, I recall a patient in her fifties who had an accident free driving record until she wore progressive lenses. Within two weeks she had scraped the side of a parked vehicle by passing too closely and reversed into a gate. Once these lenses were replaced with bifocals her driving performance was restored.
Current computer-assisted designs have minimised distortion zones and expanded the areas of clear vision, making progressive lenses the state of the art lens design for near vision problems. While there are millions of enthusiastic wearers, there are nevertheless those who are unable to tolerate this type of design.
There are a number of reasons for this intolerance. Sometimes dispensing errors, which are not obvious because of the invisible zones, can cause blurred vision and visual discomfort. However, all wearers, especially those who have not previously worn progressives, experience an "adaptive period" which can last from a few days to several weeks. For some patients this adaption period forms a barrier to success, while for others their visual demands, such as prolonged computer operation, make general-purpose progressives less suitable. For this reason success depends on providing realistic expectations as well as matching the lens with the patient's visual requirements.