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Contour plot is most common method used to represent PALs

It describes surface power of the front surfae of the lens

Identifes zones of constant surface power indicated by contour lines

It also show size of the distance, intermediate and near zone as well as the

extent and gradient of peripheral aberrations

2 types

1 Isosphere contour plots2 Isocylinder contour plots

Isosphere

! "epresents distribution of spherical power across the lens! It di#ides the lens along lines of e$ual dioptric #alues! %ach lines&shade represents increasing le#el of power at gi#en inter#al! Can easily describe location and size of near #ision zone

Isocylinder

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! 2 dimensional map that di#ides the lens into ranges of cylinder le#els

throughout the lens! 'oft design ha#e isocylinder plots located further apart! (ard design ha#e greater number of lines closed together

'ymmetrical and Asymmetrical design

'ymmetric design

In early of its generation, it employ single design that can be used as )left* or+right* lenses, with -, IP and .P are in #ertical order/ 0his causes problem in

accommodation as both eyes con#erged/

Its later generation was then rotated 1 degrees in 1 direction to create a +right*

lens and about 1 degrees in the opposite direction to create +left* lens/

isad#antages causes disruption of binocular #ision as the wearer gazed

laterally across the lens, since the astigmatism and power di3ered between the

nasal and temporal sides of the distance zone/ 0he binocular 4eld of #iew will be

se#erely restricted

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Assymmetric design

Amount of astigmatism can be ad5usted independently/

It reduces disruption in binocular #ision and pro#ides better o#erlap between the

distance, intermediate and near #iewing zones of the right and left lense

resulting in larger binocular 4eld of #iew

isad#antages 6nwanted astigmatism may be higher at the nasal side/ 0hus,

di3erences in prism, magni4cation, and power may still exit between

corresponding points on the two lenses as eyes mo#e across them