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Medical Forum / General / Vision / August 2007Reducing eyeglass prescription
I wrote a few weeks ago about astigmatism. Thanks to those who helped me understand. Here is my new prescription: OD: -1.00 SPH (+1.25 ADD) OS: -0.75 +.025 080 (+1.25 ADD) I ordered a pair of lined bifocals from Zenni, and they are great. I was really impressed with the them! That said, I believe my optometrist overcorrected me. Although I can see very sharply in both eyes at distances beyond 2 to 3 feet feet, anything from 8 inches to 2 for 3 feet is blurred. My eyes struggle to try to focus around my desk at work. So, I just take my glasses off (I can see well without my glassses). Closeup work (less than 8 inches) is perfect with the glasses on. So, I want to go down 1/4 diopter in each eye (my spheres were -.75 and -.50 for many years). The right eye would go down to -.75, but how would I reduce my left eye by 1/4 diopter? Would the +.25 cylinder need to go down 1/4 diopter like the sphere? Or would the cyclinder remain unchanged? Thanks for any help, Ed Dear Ed, I am pleased that with the advice you received you could order your glasses from Zennioptical.com In general, the SMALLEST measurement of astigmatism is 1/4 diopters. If you were measured again, you might have no astigmatism. Here is my new prescription: OD: -1.00 SPH (+1.25 ADD) OS: -0.75 +.025 080 (+1.25 ADD) Ed> So, I want to go down 1/4 diopter in each eye (my spheres were -. 75 and -.50 for many years). The right eye would go down to -.75, but how would I reduce my left eye by 1/4 diopter? Just convert the OD to "Spherical Equivalent". Ed> Would the +.25 cylinder need to go down 1/4 diopter like the sphere? Or would the cyclinder remain unchanged? Take 1/2 the astigmatic value (+0.25 diopters) and add it to the "SPH", or -0.75 + 0.125 for a grand total of -0.625 So you reduce this by 1/4 diopter to: -0.375 diopters. But they only give you 1/4 diopter increments -- so you must "round" this value up or down to either -0.5 diopters or -0.25 diopters. I hope this clarifies this issue of converting LOW VALUE astigmatism into "spherical equivalent". Also, you might check your own Snellen, just to make certain you pass the DMV with this reduced lens value. (I am an engineer, so this is just a matter of basic math.) You should consult with your optometrist to see if this conversion and Zennioptical lens is acceptable for your needs. Always make certain you pass the DMV (20/40 line) with this reduced lens combination. Otis On Aug 21, 10:43 pm, edutital...@yahoo.com wrote: > I wrote a few weeks ago about astigmatism. Thanks to those who helped > me understand. [quoted text clipped - 20 lines] > Thanks for any help, > Ed Dear Ed, Subject: Just to be safe. If you can't get to the OD for checking, here is a easy-to-use Snellen to verify that your new lens calculation is OK. Just click here: http://www.smbs.buffalo.edu/oph/ped/IVAC/IVAC.html Then press on "Display" to get letters. Pressing display again will give you new random letters. Thus you can compare your Snellen readings with the readings provided by your OD when you get to his office. Enjoy, Otis On Aug 21, 11:40 pm, "otisbr...@pa.net" <otisbr...@pa.net> wrote: > Dear Ed, > [quoted text clipped - 78 lines] > > - Show quoted text - On Aug 21, 11:40 pm, "otisbr...@pa.net" <otisbr...@pa.net> wrote: > Just convert the OD to "Spherical Equivalent". > [quoted text clipped - 6 lines] > > So you reduce this by 1/4 diopter to: -0.375 diopters. wrong Scrotis. were you really an engineer? your response is stupid. why do you explain how to calculate spherical equivalent when all he asked is how to reduce the prescription by -0.25? wow-- if you were a civil engineer and actually built any bridges I'll be sure to drive somewhere else. perhaps you were a "sanitation" engineer. perhaps you're getting a few brain tangles. On Aug 21, 10:43 pm, edutital...@yahoo.com wrote: > So, I want to go down 1/4 diopter in each eye (my spheres were -.75 > and -.50 for many years). The right eye would go down to -.75, but > how would I reduce my left eye by 1/4 diopter? Would the +.25 cylinder > need to go down 1/4 diopter like the sphere? no. > Or would the cyclinder > remain unchanged? yes. the cylinder remains the same and the sphere goes down by -0.25 For example: OS: -0.50 +.025 080 to keep the bifocal power the same as the glasses you have now then reduce the bifocal add to +1.00 if you are going to cut the minus on the top. Thanks for the information! Ed
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