Blur due to pupil area when using progressive addition spectacles.

The progression zone of a progressive addition spectacle lens cannot provide a sharp retinal image as it presents the pupil with a range of powers through which to view an object. The resulting blur is explored mathematically. The nature of this blur is extraordinary but its visual significance is very slight and is less than previously believed. Peripheral astigmatism, found in all such lenses, may lower their visual performance.