I don't have access to an NPD recommendation for inset on a +500 add. The DPD is 61mm and the NPD at 35cm on the CRP is 56mm. I know the inset needs to be moved more than 2.5 per eye, but I have not gotten an acceptable answer from the lab. They said just use the 35cm reading. Any suggestions?
Bruce
A +5.00 add has a focal length/work distance of 200mm. To determine the near PD, multiply the distance PD and the work distance, and divide this by the work distance plus 27 (the average stop distance- the distance from the eye's center of rotation to the cornea, plus vertex distance). 12200/227 = 53.74.Originally Posted by Sam Pelican
However, the vergence demand is very high when reading at a very short 8". It's not likely they'll be binocular without prism. I would call the doctor to confirm, or simply have the client hold the card and see where they place it when reading. They'll probably place it right in front of the better eye, hence very little or no inset is required.
Last edited by Robert Martellaro; 06-14-2011 at 10:24 PM.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
Thanks for the reply. The patient is new here so I l have no way to test how she holds her print. Also her old glasses had a much weaker add. Her best VA is 20/200-. I doubt she will read much with them. The Dr. is trying the strong add hoping it will help some.
That's not good. I agree- it's not likely they'll be able to read newspaper print without external magnification. I'd use a normal inset. STs only come in CR39 at this power. Walking/steps require extreme caution. The client will resist holding objects at 8"- the depth of focus will be very narrow- good luck.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
I would like to add that you should spot the Near O.C. within the bifocal at the uncut;)
stage, and use that for the seg decentration for edging. It will be more accurate.
decenter an addidtional mm for each diopter of add. so get a rd seg and decenter 5mm for each lens. Standard inset won't give you enough base in prism. It works. My LV customers in Jersey City didn;t have $ to throw around on fancy LV specs, and I learned this from Gerald Fonda MD back in the 70s who considered himself a LV guru .
Money carefully refunded
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