This video describes how to apply ANSI unwanted horizontal prism tolerances to single vision mounted lenses using the standard application method and Prentice Rule formula.
Thank you so much, this is really helpful with your way of explaining it. I really hope you post more videos, please, without the background music if you can. thanks
Hi Tracy, this video helps a lot. I have a question. It is possible for only using Prentice's rule. Sometime measuring can be not accurate.. ? Let say only determine Base direction and calculate prism diopter by Prentice's rules. Thank you so much ! :)
Hey Tran! Prentice can be used to calculate the prism effect based on the millimeter error and the power of the lens in the horizontal (180) meridian. However, the calculations are not as exact a measurement as moving the lens in the lensmeter to induce to 0.33^ in each lens. If you use the calculation method - keep in mind it generally over estimates the prism amount. Let me know if you have any other questions. Thanks for the feedback!
Hi Tracy, thank you for your answer. Yes I have one concern.. When we finish neutralizing, dot the centre of the lenses and measure PD of the first pair. You move to the second pair with out moving the table and then you realize that the second pair is having some horizontal prism. How do you know what prism it is when you only have a prescription from the doctor and you are trying to find out what the lab made...?
@@tranthu6889 when the dr prescribed prism you need to center the lensmeter power lines at the location where the prism is displayed. Ex: Rx has 2^BU in OD, then the lines are centered at 2^prism ring directly UP from the target center. Rx prism and unwanted prism are two very different things. ANSI is applied to error in Rx prism in a similar manner to non Rx prism lenses. The only difference is where original reference point is (the OC or the Prism Ref Point).
I'm trying to figure out how to determine the optical centers before reading the prism on the manual lensometer. For example, a patient brings in a pair with an outside Rx from another optical and I don't have the written Rx or PD. Can you help?
When you center the power lines at the center of the target and spot the lens - you are spotting the OC. The horizontal distance between right and left lenses OC is measured and compared to the wearer's PD. If you don't have an order ticket to compare it to or you don't have it... then just measure the wearer's PD and continue the testing method as described to determine if it meets tolerances.
@@MsTracyBennett Yes, after consulting with a couple of people, sounds like I'll have to have them put them on and spot their OC's and go from there. Thanks for getting back to me!
Great explanation.
Thank you so much, this is really helpful with your way of explaining it. I really hope you post more videos, please, without the background music if you can. thanks
Thanks! And I agree; in hindsight the background music was a mistake. Feel free to subscribe so you’re notified when I post new videos.
Hi Tracy, this video helps a lot. I have a question. It is possible for only using Prentice's rule. Sometime measuring can be not accurate.. ? Let say only determine Base direction and calculate prism diopter by Prentice's rules. Thank you so much ! :)
Hey Tran! Prentice can be used to calculate the prism effect based on the millimeter error and the power of the lens in the horizontal (180) meridian. However, the calculations are not as exact a measurement as moving the lens in the lensmeter to induce to 0.33^ in each lens. If you use the calculation method - keep in mind it generally over estimates the prism amount. Let me know if you have any other questions. Thanks for the feedback!
Hi Tracy, thank you for your answer. Yes I have one concern.. When we finish neutralizing, dot the centre of the lenses and measure PD of the first pair. You move to the second pair with out moving the table and then you realize that the second pair is having some horizontal prism. How do you know what prism it is when you only have a prescription from the doctor and you are trying to find out what the lab made...?
@@tranthu6889 when the dr prescribed prism you need to center the lensmeter power lines at the location where the prism is displayed. Ex: Rx has 2^BU in OD, then the lines are centered at 2^prism ring directly UP from the target center. Rx prism and unwanted prism are two very different things. ANSI is applied to error in Rx prism in a similar manner to non Rx prism lenses. The only difference is where original reference point is (the OC or the Prism Ref Point).
I'm trying to figure out how to determine the optical centers before reading the prism on the manual lensometer. For example, a patient brings in a pair with an outside Rx from another optical and I don't have the written Rx or PD. Can you help?
When you center the power lines at the center of the target and spot the lens - you are spotting the OC. The horizontal distance between right and left lenses OC is measured and compared to the wearer's PD. If you don't have an order ticket to compare it to or you don't have it... then just measure the wearer's PD and continue the testing method as described to determine if it meets tolerances.
@@MsTracyBennett Yes, after consulting with a couple of people, sounds like I'll have to have them put them on and spot their OC's and go from there. Thanks for getting back to me!