When I verify vertical prism in a lens (e.g. 1 pd BU), should I be able to see that prism in the lensometer regardless of where on the lens that I'm checking? For example, should I see vertical prism even if I'm not directly on the patient's designated optical center since it's supposed to be ground-in prism rather than prism from decentration?
Thanks!
If there is no power in the lens, only prism, it will be as you suggest. If there is a minus or plus power (or cyl) it will read the same as a decentered stock lens, because for all intents and purposes it is exactly the same!
I would like to add to Tallboy's response that prism is at it's best efficiency when positioned well. Rotational and beveling position on lens edge can influence the quality/quantity of prism function. Kinda like trying to get 0.25 cyl axis read in lensometer
Eyes wide open
Why would having power change the lensometer reading? Is it because I would be inducing decentered prism into the reading depending on where on the lens that I'm taking the reading?
If so, then how can I "insure" that the patient is getting the correct amount of prism other than, I guess, making sure that he/she is looking through the optical center? Also, even if there is power in the lens, should I still be able to read the prescribed prism at the patient's optical center? Maybe optical center is not the correct term. How can I "insure" that the patient is receiving the prism through where his/her pupils are looking through the lens (the pupillary axis)? Also, should I be able to read the prescribed prism where the pupils are looking through the lens?
Thanks!
Originally Posted by Tallboy
Last edited by Neophyte Optician; 12-22-2017 at 03:55 PM.
If you ordered the spex with a specified OC Ht, yes. If not, you will need to read it at the datum. You will also need to “anchor” the reading by determining the lens with the highest power at the 90. If the lens w/o prism has the highest power at the 90, spot it and without moving the table, check the other. If the lens with the highest power at the 90 is the one with prescribed prism, then spot it with the 1D prism and without moving the table, check vertical on the other lens. This will tell you if the prism is correct. You will also need to compare it to ANSI.
This is is the best I can offer, as the RX has not been provided to us.
The Rx is: OD -7.00-0.75x135 with 1 pd BU
OS -7.50 with 1 pd BU
Thanks!
Great. This helps. Spot the OS so it is centered in the reticle, as this is the higher RX @ the 90, then read the OD prism. If all is good, the OD should spot on the 1D (BU) grid on the reticle.
Since the powers are are very similar, there is minimal separation due to OC variance.
Both eyes base up prism? Whom prescribed yolked prism?
For some reason, I read this as prism on OD, not yoked. Been on PTO this week. Maybe my brain is a bit muddy?
You may want to back off the Makers Mark and switch to Busch beer....Worked for me..
Treat your local independent brewer as you would like them to treat their local independent eye care provider.
Quit feeding the (InBev) beast.
This thread is filled with typos! I recommend that everybody lay off the sauce for at least a couple of days.
Best regards,
Robert 'Snowman' Martellaro
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.
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