Quickly Calculating Contact lens RX from Spectacle

[Ante cibum]

So, the other day I stumbled upon this article that allows one to quickly calculate a contact lens RX on the fly from someones spectacle lens RX.(/how-to-rapidly-determine-a-contact-lens-prescription/)

I'm curious if my calculations match up with old contact Rx. Here's my spectacle lens Rx and here's what I calculated for the contact lens.

Spectacle
OD: sphere -1.00, Cylinder -2.75, Axis 180
OS: Sphere -0.50, Cylinder -2.50, 200 (O.D. wrote 002...I assume typo)

Contact lens I calculated, let me know if I did this right.(I assume BC/Dia same from dated contact Rx)

OD: -.75, -2.25 x 180 BC 8.6 Dia 14.5
OS: -.5 - 2.0 x 200

The poster said it should be .25 off, for some reason, but mine matches. My dioperes match to my Rx exactly but both of the cylinder are off by -.5 How off am I?

Thanks!

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[DrVinzKlortho]

Hmm lots of problems here and I'm not sure where to begin. For starters the axis measurement goes from 001 to 180 degrees. It should be written with zeros in front if less than 100 to avoid confusion and transpositional errors e.g. 090, 002, etc. Most contact lens toric/astigmatism prescriptions (ie yours) start with -0.75 Diopters of cylinder and go up in increments of -0.50 D, although exceptions do exist. There is a formula which you can use to calculate your contact lens Rx but it really doesn't affect your Rx that much so I won't get into it.

 

[Ante cibum]

Well, my left eye used to be 170 axis, so that's why I thought it was an error(002). Basically I want to know if I can still use my old Rx to see as well, modifying it with the information from the new spectacle lens.

Sorry, I see how my question may be confusing, it was a little muddled.

 

[OpticalBlackOut]

It sounds like you're trying to order contact lenses by using a glasses prescription.
You would need a valid signed and unexpired contact lens Rx that needs to be verified through a fax number with an optometry office. There were also quite a lot of errors (i.e. axis 200 doesn't exist).

 

[itek2OD]

Hmm lots of problems here and I'm not sure where to begin. For starters the axis measurement goes from 001 to 180 degrees. It should be written with zeros in front if less than 100 to avoid confusion and transpositional errors e.g. 090, 002, etc. Most contact lens toric/astigmatism prescriptions (ie yours) start with -0.75 Diopters of cylinder and go up in increments of -0.50 D, although exceptions do exist. There is a formula which you can use to calculate your contact lens Rx but it really doesn't affect your Rx that much so I won't get into it.

perfect use of that gif - someone always beats me to using that gif

 

[thiaeyemd]

I am an ophthalmologist and don't do contacts but you need to get a trial contact lens from an OD and get this sorted out. I have had two patients over the years try to reverse hack their glasses prescription or contact prescription to order new contacts etc... All that happened is that they couldn't see well...ended up ordering the wrong contacts and sabotaging themselves. Just spend the money on a $50 exam.

 

[DrVinzKlortho]

I am an ophthalmologist and don't do contacts but you need to get a trial contact lens from an OD and get this sorted out. I have had two patients over the years try to reverse hack their glasses prescription or contact prescription to order new contacts etc... All that happened is that they couldn't see well...ended up ordering the wrong contacts and sabotaging themselves. Just spend the money on a $50 exam.

Whoa don't cheapen my profession anymore than it has already done to itself. I charge $51 for a fit. $52 for a toric fit.

 

[20DOC20]

Do you know Auto-CAD? The angles for the astigmatism are defined exactly the same as that program, except that we always deal with a positive y axis. So, you'd never write axis 200, because that angle is in the -x and -y field.

3 o'clock is the zero point. 9 o'clock is 180 degrees. Simple. You aren't an optometry student, obviously, so why should we answer your question? Go get an eye exam.

 

[Commando303]

So, the other day I stumbled upon this article that allows one to quickly calculate a contact lens RX on the fly from someones spectacle lens RX.(/how-to-rapidly-determine-a-contact-lens-prescription/)

I'm curious if my calculations match up with old contact Rx. Here's my spectacle lens Rx and here's what I calculated for the contact lens.

Spectacle
OD: sphere -1.00, Cylinder -2.75, Axis 180
OS: Sphere -0.50, Cylinder -2.50, 200 (O.D. wrote 002...I assume typo)

Contact lens I calculated, let me know if I did this right.(I assume BC/Dia same from dated contact Rx)

OD: -.75, -2.25 x 180 BC 8.6 Dia 14.5
OS: -.5 - 2.0 x 200

The poster said it should be .25 off, for some reason, but mine matches. My dioperes match to my Rx exactly but both of the cylinder are off by -.5 How off am I?

Thanks!

What's the point of your question? If you're trying to order contact lenses with your spectacle prescription, this is a poor idea. With the amount of astigmatism present, rotation will be important in determining the final lens, and evaluating rotation will require observing a contact lens on the eye.

 

[310]

What's the point of your question? If you're trying to order contact lenses with your spectacle prescription, this is a poor idea. With the amount of astigmatism present, rotation will be important in determining the final lens, and evaluating rotation will require observing a contact lens on the eye.

I know they teach you that in school, but in reality the modern contacts don't really rotate. Pick something close to their axis and they come in happy and seeing 20/20.

 

[Commando303]

I know they teach you that in school, but in reality the modern contacts don't really rotate. Pick something close to their axis and they come in happy and seeing 20/20.

I'll be quick to admit I have very little clinical experience, but I certainly have seen a few patients with significant lens-rotation, for which I ended up compensating in the final order. I don't believe the original poster would be wise to order toric C.L.es based on a hack of his spectacle prescription.

 

[310]

Low base curve Acuvue Oasys and Biofinity Toric generally won't rotate to the point where it matters.