Editing Progressive lens (section)

==Disadvantages==

''Peripheral Distortion:'' Progressive lenses suffer regions of [[Aberration in optical systems|aberration]]s and geometric distortions in the periphery, leading to poor vision when turning the eyes down and to the sides. Different designs of progressive lenses have more or less of this distortion.

''Fitting:'' Progressive lenses require careful placement relative to the wearer's pupil centre for a distance-viewing reference position. Incorrect specification of the fitting location can cause problems for the wearer including (depending on the design of the lens) narrow fields of view, clear vision in one eye only, on-axis blur, and the need to alter the natural head position in order to see clearly.

''Cost:'' Progressive lenses are more expensive than [[Bifocals|bifocal]] and single-vision lenses due to higher manufacturing and fitting costs. Some research has been conducted to reduce the fabrication cost by precision injection molding.<ref name="test">{{cite journal|title=Simulation and measurement of optical aberrations of injection molded progressive addition lenses|author1=Likai Li |author2=Thomas W. Raasch |author3=Allen Y. Yi  |name-list-style=amp |journal=Applied Optics|year= 2013 |volume=52|issue=24|pages=6022–6029|doi=10.1364/AO.52.006022|pmid=24085007 |bibcode=2013ApOpt..52.6022L }}</ref>

When recommending a progressive lens design, an eyecare practitioner will usually ask the customer some questions about their lifestyle, which coupled with prescription restrictions or recommendations and cost can establish the suitability of various models of progressive lens. Different lenses have different glazing restrictions, lens material availabilities, maximum and minimum fitting heights, prescription ranges and as such the variation in quality between higher and lower end varifocal lenses is considerable.<ref>{{cite journal|title=Progressive addition lenses—measurements and ratings|vauthors=Sheedy J, Hardy RF, Hayes JR|url=http://commons.pacificu.edu/cgi/viewcontent.cgi?filename=0&article=1018&context=compvision&type=additional|journal=Optometry|year=2006|volume=77|issue=1|pages=23–39|doi=10.1016/j.optm.2005.10.019|pmid=16458243|access-date=2013-06-16|archive-date=2010-06-14|archive-url=https://web.archive.org/web/20100614133821/http://commons.pacificu.edu/cgi/viewcontent.cgi?filename=0&article=1018&context=compvision&type=additional|url-status=live|url-access=subscription}}</ref>