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| Author | Subject: prismatic effect for bifocals and oblique axis cyls |
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 irb
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prismatic effect for bifocals and oblique axis cyls
Jul 07, 2007 15:47:19 hi all hope you are all ok!! i have a question about working out vertical differential prismatic effect i understand that for a single vision lens you use p=cf to work out the vertical differential prismatic effect at near. however i am a little confused about working out the differential prismatic effect when dealing with bifocals, when we are given the distance prescrition and the add, do we add the power along the vertical meridian (distace rx)to the add and then multiply this by the vertical decentration to give the primatic effect? also i was going through my uni lecture notes i found a formula (involving sin and cos) for working out the vertical primatic effect when the axis is oblique. i was wondering if there was a shorter method of working the above out, which we could use in an exam situation? many thanks |
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Stephen Meynell
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RE: prismatic effect for bifocals and oblique axis cyls
Jul 07, 2007 20:20:17 Hi again irb - Bifocals are the same as ordinary distance glasses as long as the nead Add is the same for both eyes and the seg height and design is the same. So for (eg) RE +2 add +2 LE +4 add +2 Then 1cm below optic centre te prism induced is 2 dioptre prism bae up left eye. I know of no easy method with oblique cyls - Sorry |
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irb
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RE: prismatic effect for bifocals and oblique axis cyls
Jul 11, 2007 20:07:22 hi steven thanks |