Big change in prescription; not vision though. Bad dr?

[Blown2go]

Went in for a routine eye exam and had 20/20 vision with a prescription of od -2.25,.75 118 os 3.0, -1.25, 070 and walked out with a new prescription of od -3.25, .75, 035 os -4.5, 1.25 155. Why such the big change when the vision was perfect before? I don't get it?

Was a reputable place but felt like an in and out no craps given place. Should I even fill this prescription?

[Blown2go]

Thank you for the explanation!!! As a professional in the aviation business I am used to standards and alignment and would have never expected differences in a prescription!!!! Learn something new everyday! Thank you all for taking the time out of your day to explain as my eye doctor just said yes it's a change! Thanks again!

[JohnHaganMD]

sure happy to help.

[Blown2go]

Does one make for a better lens or is it the exact same lens?

[JohnHaganMD]

exactly same lens.

[SoftwareDeveloper]

As the doctor says, its like converting between kilograms and pounds. There are 2 different ways of writing astigmatism prescriptions, the plus method and the minus method. This article explains how to read your prescription.

There are calculators on the net to convert from one to the other. Here are the two prescriptions both written in minus form:
OLD-minus;
OD -2.25, -.75 118  
OS -3.0, -1.25 070

New-minus:
OD -2.50, -0.75 125  
OS -3.25, -1.25 065

Here are both prescriptions in plus form:

OLD-plus:  
OD -3.00, +.75 28  
OS 4.25,+1.25  160

New-plus;
OD -3.25, +.75 035
OS -4.5 +1.25 155  

The two differ by only 0.25 in sphere, which isn't much since they only measure to the nearest 0.25, i.e. you won't see a prescription like 0.67. That is only a small difference. If the "real" value is say 0.67 it might be measured as 0.5 as the closest notch, whereas 0.69 might be measured as 0.75 as the closest notch.  That can be minor measurement error, using different equipment or a different doctor, or the reality that people's vision can change a small amount during even one day.  The angles only differ by a slight amount, but it might just be slight measurement error, this isn't an exact reading or a slight shift.

[SoftwareDeveloper]

oops, forgot the link. This article explains how to read the prescription:

http://www.usaeyes.org/lasik/faq/read-eyeglasses-contacts-prescription.htm

[SoftwareDeveloper]

oops, typo, missed the "-" on the old-plus, to avoid more confusion, for the plus notation  it should have been:

OLD-plus:  
OD -3.00, +.75 28  
OS -4.25,+1.25  160

New-plus;
OD -3.25, +.75 035
OS -4.5 +1.25 155  

[JohnHaganMD]

Most people cannot tell differences of plus/minus 0.25 cylinder or 5 degree of axis shift

[Blown2go]

There was a typo - original prescription on the cyl all was negative. The new the cyl is positive.
OLD; OD -2.25, -.75 118  OS -3.0, -1.25 070
New; OD -3.25, +.75 035 OS -4.5 +1.25 155

I guess I don't understand as I've never had a cyl that was positive. Is that why the sphere is greatly increased and axis is so much different due to the positive cyl? I just assumed there was standardization amongst eye prescriptions?? Excuse my ignorance ahead of time! Thanks folks!

[JohnHaganMD]

No there is no standardization. They both are correct. Just think of it like lbs. vs kilograms. Before grinding opticians change to minus cylinder. Again those two Rxs are almost exactly the same.

[JohnHaganMD]

You left out a very important part of the glasses RX which is a plus or minus sign before the middle number (cylinder).  I relatively certain the one RX is written in PLUS cylinder form and the other MINUS cylinder form. That being the case the RXs are virtually the same. It's like your weight looks a whole lot different when written in pounds than when written in kilograms. If you want a detailed explantion look anyplace on the web for the formula to turn one into the other. In any case very little difference.

[SoftwareDeveloper]

The "-" is included in the cylinder for the first OS prescription (which supports your guess, as do the angles), and for sphere. So the question is just whether it was accidentally left off off the OD one. If so, without doing the  exact calculation, at first glance it does appear they are close. There is some minor variation between refractions done by different people, using different equipment, and even the same person's refraction can vary a bit throughout the day when having the same person test it.

[JohnHaganMD]

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