A design pattern for principle meridian of progressive addition lenses
The meridian design is one of the keys for the ophthalmic progressive addition lens design.A new prin-ciple meridian model,giving out the calculation formula of the power at principle meridian is proposed.Two examples of progressive addition lenses with different additional power are designed,manufactured and tested under this formula.The power and astigmatism contours of the two lenses are presented.The results show that for the short-channel lenses with an additional power of 1.25 D,the near zone is reached 7-8 mm below the geometric centre and the maximum a-stigmatism in both blind zones is 1.25 D.For the longer-channel lenses with an additional power of 2.5 D,the near zone is reached 11 mm below the geometric centre,and the maximum astigmatism in the blind zones is 2.25 D.The principle meridian pattern can be applied to design the progressive addition lens with different addition power,same measurement point at reading area and various progressive corridor.It allows the wearers have more choices and com-fortable visual effects,brings convenience for quality inspection in manufacturing process,cut down the production costs,thus improves the popularization of the of progressive lens.
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